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Thursday, August 9, 2012

New Jersey Gemstones

A variety of tumbled gemstones
Scanned by Adrian Pingstone

Amber that has been preserved since the age of dinosaurs is found in several places in New Jersey where there are Cretaceous rocks one of these places in the area around Sayreville although they can be found scattered throughout the Cretaceous rocks and various localities throughout southern New Jersey. Although there are several deposits of Cretaceous aged rocks in the United States Amber is only found with appreciable quantities in New Jersey.

Amethyst is found in the many trap ridges of New Jersey in both the area of the Palisades and in the Ramapo Mountains.  This variety of quartz is usually found in the cavities in the rock. Many other minerals of the zoisite family are also associated with traprock quarries.

In the past there was extensive zinc mining activity in Franklin and Sterling Hill in Ogdensburg that produced large quantities of zinc minerals.  The mine dumps in these areas are one of the most noted areas in the United States that have produced fluorescent minerals.  Some of these minerals are gemstones in their own right notably rhodonite and sphalerite.  In addition Sussex County is also known for producing other minerals including aragonite, corundum, garnet, pyrrhotite, rhodonite, spinel, tourmaline and williamsite.

Bergen County has produced amethyst, natrolite and opal that are found in the county’s trap ridges.

Mercer County has been known to produce albite, calcite, chabazite, datolite, natrolite, stilbite and tourmaline. Calcite, chabazite and datolite are produced from the trap ridges in the county.

In the far southern part of New Jersey can be found quartz crystals that are called by many Cape May diamonds although the source of these stones remains unknown it is thought they are washed down from some underwater formation further upstream in the Delaware River.  They are found on the beaches of Cape May and surrounding communities at the mouth of the river. The same area also produces jasper. 

Corundum has been found in Sussex County associated with the Franklin limestone as almost perfect crystals seen in cavities in the limestone.  These stones are blue, grey and red that in some places are clear enough to be cut into gems. 

Other counties where gemstones can be found include:

Middlesex - marcasite, petrified wood, pyrite

Morris - carnelian, serpentine

Passaic - agate, amethyst, carnelian, chabazite, datolite, heulandite, pectolite, prehnite

Sussex - aragonite, corundum, garnet, pyrrhotite, rhodonite, spinel, tourmaline, williamsite

Union - calcite, chalcedony, prehnite, sphalerlite

Warren - calcite, chalcedony, garnet, molybdenite, prehnite, serpentine, sphalerlite

Most of the collecting sites are located in Northern New Jersey.  Many of these sites are found at old mines or rockcuts.

Tuesday, July 24, 2012

The Great Arizona Diamond Swindle

Ship Rock close to the diamond fields

The guys that dreamed up the Great Arizona Diamond Swindle sure did a good job of it, and one that sucked in some smart money from both coasts.  Its locality was way out in the boonies of New Mexico.  Bluntly it was salted with uncut stones from Africa where vast amounts of diamonds were found in the newly discovered kimberlite deposits.  The so-called rubies that accompanied the diamonds turned out to be garnets that were mistaken for rubies. The swindlers salted so many diamonds of the property that even after the swindle was exposed people were still finding diamond crystals on the site.

This was a well organized swindle based on the idea in many American’s heads that the West was a treasure house of riches waiting to be tapped.  At the time companies were organized to tap these riches, and the locality the swindlers chose in New Mexico was made for a swindle.  At this locality there were not only diamonds, but rubies, emeralds and sapphires too.  This scheme got off the ground in 1870 that was represented in San Francisco by Phillip Arnold and John B. Slack who claimed to have found precious gems in the Territory of New Mexico.  On their part they showed off more then 80,000 carats of rubies and a large quantity of diamonds including one crystal weighing 108 carats.

A large group of investors visited the diggings and collected a large number of gemstones that were literally scooped off the ground, and returned to San Francisco where the gems were put on display so other suckers could be reeled into the scheme. At the time someone remarked it was not expected they could pick them up by the bushel, but there they were.

They even roped in the Federal Government because on May 10, 1872 a bill was passed in Congress in the interests of the diamond miner who had made the discovery.

A larger expedition was planned that included a mining expert that had graduated from the Royal School of Mines in Freiberg, Germany.  This expedition was expected to last for sixty days.  This expedition left Rawlings, Wyoming on May 28, 1873 going southwest to the gem mines, but after a while they claimed they had lost their way and proceeded northwest for several days.  Some of the party began to doubt the truth od the scheme, but finally after a circuitous route then finally arrived at the site, and the mountain promised to be a real Golconda.  Everybody found gems, and gems aplenty with their hope rising accordingly.

A third party set out late in the season to return to this fabulous locality, but never got there, and this expedition was abandoned.  When Clarence King the head of the United States Geological Survey heard this third expedition had come to naught he organized an expedition of his own.  It was King’s expedition that proved the whole scheme was a Humbug and brought the whole scheme crashing down around the ears of the plotters. It's estimated this pack of crooks got around $750,000 in 1870s dollars.

The Diamonds of the Wyoming Craton

Bedrock map of North America   USGS

This is a tale about how riches were overlooked in Colorado, Montana and Wyoming by gold seekers in days of yore.  In these three states a whole diamond province has been overlooked in the kimberlites by the hundreds that underlie these states.  The diamonds can also be found in lamproites, lamprophyres and other cryptovolcanic structures that are associated by the Wyoming Craton underlying these three states.  Many of the larger targets lie right next to I-80 between Cheyenne and Laramie that remain unexplored.  This area was originally discovered by early gold miners who discovered it contained little or no gold so they passed it on.

Subsequent discoveries indicate this may be one of the most unexplored diamond provinces in North America where the diamonds can be found in the carbonate rich sediments found in a Archean gneiss.  More then fifty depressions have been discovered here suggesting cryptovolcanic activity that lie east of the State Line diamond district.  It is thought these depressions could be kimberlites containing possibly large amounts of diamonds. 

Ongoing exploration suggests that the Wyoming Craton contains a world-class diamond province and like the diamond province near Marathon, Ontario also contains large deposits of colored gemstones as rubies and sapphires.  This craton is found covering a large portion of Canada.

The Wyoming Craton aside from covering several western states also includes exposures in Alberta and Saskatchewan. Diamonds have been discovered in both the kimberlites and lamprophyres in Montana, Wyoming, Colorado, Kansas and Nebraska as well as Canada.

Another potential place where you can look is in any conglomerates that are derived from the lamprophyres and kimberlites of the Wyoming Craton.  One of my prospecting buddies has found a diamond deposit like this near Marathon, Ontario.  Another Canadian prospecting buddy that lives in western Ontario has also found probable diamonds in his part of the province.

It isn’t just diamonds that can be found there; recently one of the world’s largest deposits of rare earth metals was found in Nebraska,  When you start poking around in this ancient craton you never know what you’re likely to find.

The Wyoming Craton has the greatest southwestern outcrops of Archean rocks in North America.  Theoretically terranes like this have deep roots in the lithosphere that according to Clifford’s rule this deep keel is necessary for the formation of kimberlites with their association with diamonds.  Although this terrane wasn’t deformed during the
Ancestral Rockies Orogeny it was pervasively deformed during the Laramide Orogeny and one theory has it that its deep keel was removed partially or wholly allowing it to be deformed during the Cretaceous or later.  

Monday, July 23, 2012

Finding Diamonds in California

Uncut diamonds

From the earliest days of the California Gold Rush diamonds were found in the tailraces of sluice boxes that were used for gold washing.  Diamonds were found not only in recent stream gravels but much older gravel that was buried under layers of lave and tuff from ancient volcanic activity as fossilized stream channels that ran along the mountains from north to south.  These stream channels indicated an ancient stream flow that was almost at right angles to the present day flow.

The biggest problem with California diamonds is there just are not enough to make going after them profitable. Most of the stones have been found as a result of gold washing operations in both present day streams and in the fossilized beds of earlier streams. Many of the diamonds were destroyed by the use of stamp mills used the breakup the gold ore retrieved from the fossilized streambeds. Their presence was noted as fragments seen in the gold ore. The diamonds that were recovered from ore were for the most part small or industrial grade diamonds.

As early as 1853 diamonds were discovered on top of Table Mtn. about thirteen miles north of Oroville on state Highway 70 close to the ghost town of Cherokee.  It was in the gold diggings surrounding the town that reportedly more then 300 diamonds were found most of them being of industrial grade.  Claims have been made that at the time this was the largest discovery of diamonds made in North America.  This has been exceeded with the discovery of several diamond producing areas in Canada.

Cherokee was the site of the only diamond mine in California, and it was here the first diamonds were found.  Mike Maher discovered a perfect blue diamond when he was cleaning out his sluice box in 1866.  Other diamonds were found here with one of them weighing six carets, but because gold was the primary concern it is unknown how many millions of dollars worth were discarded with the mine tailings produced by the hydraulicing for gold with high pressure jets of water that washed away the gold ore.  

The fact that diamonds do occur in California is well attested to in newspapers and scientific journals.  In some cases however it is readily apparent that many of these so-called diamonds were in fact quartz crystals that had become rounded because of stream action.  One such quartz crystal had been used as a marker in a game of marbles where it show several percussion marks that were the result of being hit by marbles.  A diamond would not show such percussion marks, but would rather cleave into pieces instead waiting to be found in the sluice boxes at work in the area.

Sunday, July 22, 2012

The Georgia Marvel and other would be gemstones

A large crystal of sapphire from Madagascar
Photo by Rob Lavinsky 

This was found in a stream in the Blue Ridge Mountains of Georgia in 1883 and was purported to be a sapphire worth $50,000 by its finder who was assured of its authenticity by two different southern jewelers.  This fabulous find was also known as the Blue Ridge Sapphire.  The jewelers had arrived at a value for the stone based on its weight of several carats.  Eventually this stone was proved to be a hunk of rolled blue-bottle glass that took coating it onto some platinum wire to convince its finder.

This is a glaring example of how little the average person knows about gems and it seems that fallacy more then truth is known by the general public.  One of these fallacies is the belief that any stone that can be scratched by a file has to be glass.  Another is that is when a stone is hit with a hammer it’s a fake.  These practices have led to the destruction of many valuable gems.

The United States has an abundance of all types of gemstones that has never been appreciated by the average person.  In many cases these gems have been produced as a byproduct of other mining operations where many of them have slipped through the operation to be lost.  Many of the stones that were saved were discovered in places where gold was being washed with the miners being attracted to a gem because it was a shiny pebble.

Gold washing was not limited to the western US, but was also practiced in the South starting in the early 1800 with the discovery of gold in North Carolina.  It is difficult today to appreciate the size and scope of these southern gold deposits that ran through the Piedmont and Blue Ridge Mountains.  In many cases the stream banks for miles were covered with mine tailings. 

The gold wasn’t limited to placer deposits, but many mines were also producing lode gold.  Many of these mines were destroyed during the Civil War.  Recently the Haile Mine in South Carolina was found to have reserves of gold exceeding 3,000,000 ounces.  A Canadian mining company is in the process of reopening this mine.

Another of these wonders was a stone weighing more then nine ounces that was discovered near Gibsonville, North Carolina that was deemed to be a real emerald by some local expert by some “local expert.”  A microscopic examination of this stone contained numerous small sparkles of light that were thought to be tiny diamond crystals.  This stone was eventually proved to be a quartz crystal having long hail-like crystals of hessonite and actinolite that also had a series of small bubbles in a stream-like pattern filled with liquid that sparkled in the light like diamonds.

In truth the United States has produced virtually all the precious and semi-precious stones in the world.  For the most part these stones remain in the ground through lack of interest of outright ignorance.  There is also a prevalent belief that gems come from some far-off romantic place that it is difficult to reach from here.   

Saturday, July 21, 2012

The easy way of Identifying your gemstones and minerals

Semi precious gemstones
Photo by Mauro Cateb

All gemstones are minerals, but not all minerals are gemstones, so the limited knowledge imparted here can be used on both gemstones and minerals.  If you can’t tell what kind of gems you own don’t feel bad because there have been plenty of emperors and kings that didn’t have a clue about what kind of stones they had in their own crown.  A good example of this is the Black Prince’s Ruby that resided in the Crown of England for hundreds of years before somebody found out it was really a mineral called “spinel.”  This is a stone that looks like a ruby but is a much less expensive stone then real ruby.  Clear white topaz is often mistaken for diamond and in the past many large diamonds have been found to be really topaz.  Identifying these stones is in the realm of the gemologist who is specially trained to identify gemstones.

A translucent ruby
Photo by Rob Lavinsky

There are several stones that are treated as gemstones, but aren’t.  Amber is a glaring example of this, a stone that is treated as a gem but in reality is fossilized tree sap having many inclusions of insects and other organic matter.  Petrified wood is another example that is often beautiful and is treated by many as a gemstone, but isn’t.  Jet, the black stone is actually a variety of coal and far from the definition of a gemstone, as are pearls.  Pearls have the distinction of being the most valuable stone, but they aren’t gemstones either.

Identifying gemstones and minerals is really a process of the elimination, for instance if you are presented with a green clear gemstone it is not apt to a ruby. More than likely it is emerald, but you really can't be sure without further tests. There is a variety of garnet called demantoid that is also green and is often mistaken for an emerald. One of the most important tests that are used in mineral identification is the color of the stone.

Hardness is another criterion that is used. This is based on the Moh’s hardness scale that ranges from 1 to 10 with diamond being the hardest and soapstone the softest. Most stones that are used in making jewelry are harder than seven on the Moh’s scale even though some stones that are as soft as three on the Moh’s scale are faceted for collectors. You can buy hardness testing kits or make your own from various minerals that work’s as good as store bought.

Turquoise from Mojave County, California
Photo by Rob Lavinsky

The looks of the stone are important is it transparent, translucent or opaque.  Transparent means can you see through the stone so things can be seen clearly that are behind the stone.  Translucent means does light pass through the stone, but you can’t make out objects that are in back of the stone.  Opaque means light doesn’t pass through the stone, and you can’t see through it.

Streak is literally a thin mark of the mineral or gemstone composed of very fine powder left on a piece of unglazed porcelain colored either black or white.  Black is often used to test for gold and other precious metals when it is known as a “Touchstone.”  It is often used in conjunction with acid to see if there is a reaction between the streak and the acid.  The karat weight of gold can be determined by treating its streak with various concentrations of nitric acid.

2x2 inch black and white streak plates,  White is pyrite and black is rhodochrosite

We sell streak plates: Click Here 

Cleavage and fracture are other important tests.  Fracture is most important for quartz gemstones that break in a Concoidal fracture that looks like little clam shells.  Some minerals like jade have a hackly fracture i.e. a rough appearance.  Some stones have a pronounced cleavage like topaz or diamond.  Topaz is especially prone to a perfect basal . cleavage causing it to be a poor gemstone.

Specific Gravity was discovered by Archimedes when he was tasked to find out if a gold smith cheated the Tyrant of Syracuse when he was making a golden crown for the tyrant.  This was a job that required quite a lot of forelock tugging on the part of Archimedes until he finally threw his hands up and decided to take a hot bath. His slave girl filled the bathtub to full of hot water so on Archimedes claimed into the tub it overflowed. He had discovered the principle of specific gravity, and with that he jumped out of the bathtub and went streaking through the town agora of Syracuse yelling at the passersby Eureka, Eureka that means I have found it, I have found it. They all thought he had gone nuts, and if it wasn't for the fact his brother-in-law was the tyrant he will probably been slapped in jail.

What Archimedes discovered was the body would displace an equal amount of water according to its volume, or in modern terms its weight per cubic centimeter. This is normally taken by first weighing the object in air and then weighing in water. The difference is its Specific Gravity.

These are some simple tests that can help with gemstone or mineral identification there are others that are far more complicated that can be used in conjunction with the simple tests. Although there are over 2000 recognized minerals in the world there are only about 300 that are common rock forming minerals that you are apt to encounter in the field. A good source of information about most minerals can be found at

Thursday, June 28, 2012

What Diamond Crystals look Like

Interpenetrating cubes of diamond
Photo by Rob Lavinsky

The word morphology means what it looks like.  Diamond crystals are a good example of this as in the growth process they are able to take on many guises.  They all however are caused by the basic shape of the carbon cell that controls the diamond growth.  The carbon cell is used to build the diamond crystal or stated in another way a diamond molecule.  These carbon cells are deposited onto the nucleus of the diamond one layer at a time until the diamond finishes growing.  In its purest form a diamond crystal is cubic like a crystal of sugar.  The addition of various elements however causes a diamond to morph into different shapes or colors.

The most common of these shapes are the cubic form that is square like a salt crystal or the octahedron which is two pyramids stuck together base to base.  From this simple crystal form the shape of a diamond becomes more complex.  This is caused by many different physical process; the most common being the physical space allotted to the diamond crystal to grow.  If this allotted space is cramped and not shaped like a typical space the diamond crystal will grow into the shape of the space.   Something that will further complicate the final shape of the diamond crystal that is delivered to the surface of the Earth is the dissolution of the diamond in carbonate or silicate bearing water at the pressure-temperature conditions encountered in the diamond stability field.  This was established experimentally by Alexander F. Khokhryakov and Yuri N. Pal.Yanov of the Siberian Branch of the Russian Academy of Science in Novosibirsk Russia

The macle another form of diamond crystal
Photo by Rob Lavinsky

One of the stranger forms of diamond growth is exemplified by the rough diamonds from the Ekati, Diavik and Snap Lake mines in Canada.  These diamonds are dug out of the ground wearing fur coats that are fibrous overgrowths of diamond crystals with a transparent diamond crystal at the center.  Apparently somebody told these diamonds they were coming from Canada, so they came prepared for the Canadian weather.  How this came about was the diamond crystal had more then one stage of growth. 

There are one or more generations of crystal growth in most diamond crystals.  A diamond crystal can also undergo retrograde growth where conditions either in the area in the mantle where it was formed or on its way to the surface in kimberlite magma.  Some of these crystals can become bizarre in their appearance, and some of the more bizarre are what are called skeletal crystals.  Sometimes the diamonds are etched into more rounded shapes by the action of the chemistry of where they are formed or transported.

The macle is another shape the diamond can naturally take this is a twinned diamond taking a triangular shape and has two large triangular sides.


Harlow, George E., The Nature of Diamonds, American Museum of Natural History, © 1995

How Diamond Crystals Grow

A diamond crystal from Crater of Diamonds State Park, Arkansas
Photo by Rob Lavinsky

Diamonds don’t grow overnight because in nature their growth proceeds one atom of carbon at a time with four carbon atoms bound together by chemical bonds.  The natural way that this bonding occurs will normally create a crystal that is an octahedron in shape.  This shape however can be altered by several different parameters imposed by the space allocated to the growth of the crystal in the media in which it is formed.  In the process of growing diamonds are apt to include small crystals of the surrounding material into their crystal shape.  These inclusions are literally windows into the mantle of the earth that are brought to the surface when the diamond is carried to the surface of the earth by a kimberlite or lamproite.

Diamonds are nothing more complicated then a crystal of pure carbon, and are in fact an allotropic form of an element that can have other crystalline forms either amorphous as lampblack or as graphite from which we make pencils.  There is another rarer amorphic form of carbon termed ‘lonsdalite’ that is somewhere between graphite and diamond in physical structure.  Lonsdalite is not a variety of diamond but is instead a different material.  In lonsdalite there is a repeating networking of carbon atoms that all point in the same direction rather then alternating back and forth as in a diamond.  Its crystals instead of forming cubes or tetrahedra as the diamond does are instead hexagonal.  Although it is often found with diamonds it is considered to be an allotropic form of carbon formed as the result of shock from a large meteorite.

From work performed on some of the diamonds from the Ekati diamond mine in the Northwest Territories of Canada it would appear that the growth of diamond crystals begin with a small fragment of graphite upon which the diamond crystals are deposited over time.  A matter of controversy is the actual speed in which diamond crystals are formed.  Experiments in Japan with manmade diamond crystals suggest that it is possible to grow a ten caret crystal in several hundred hours.  This of course is under ideal conditions and in nature would probably take much longer as the diamond crystal would have to scavenge its carbon atoms from the surrounding rocks.  Carbon is a rare element in the earth’s rocks.

Most of the carbon available to create a diamond has been postulated to come from oceanic crust that has been subducted beneath a continental crust as deceased life forms of coral reefs with the necessary temperature to cause their disassociation into the components making up the coral reef.  This would be carbon and the carbonate radical.  The calcium or magnesium from this reaction would be incorporated into the earth’s mantle.  Whatever free carbon remains from this reaction would be available at this temperature and pressure to form diamond crystals.

As the diamond crystal grows it is also scavenging other elements that are incorporated into the crystal as crystal defects.  The most common of these elements are nitrogen and iron.  These elements cause the diamond crystal to become colored with the coloration being dependent upon the amount of these elements.

Harlow, George E., The Nature of Diamonds, American Museum of Natural History, © 1995
Mineralogical Association of Canada, Editor Lee A. Groat, Geology Of Gem Deposits, Short Course Series, Volume 37, Yukon Geological Survey, © 2007, Yellowknife, Northwest Territories
Gem Deposits,
Geology of Gem Deposits, Mineralogical Association of Canada, Editor Lee A. Groat,  Volume 37 © 2007

Kimberlite the source for Diamonds

Kimberlite is a potassic volcanic rock best known for sometimes containing diamonds.  It was originally discovered in Kimberly, South Africa in 1871 hence its name.  The miners digging in the “big hole” found a large diamond weighing 83.5 carets that spawned the South African Diamond Rush.  There have been literally thousands of kimberlites that have been discovered since the initial discovery in 1871.  Of all the discoveries however only about one kimberlite in three hundred actually become diamond mines.  Diamondiferous kimberlites are actually quite rare.

In cross section a kimberlite is a vertically standing feature called a diatreme in the earth’s crust that is shaped like a big carrot.  Where in the earth’s mantle kimberlites originate has been a matter of controversy for decades the one thing we are sure of however that they come from a depth greater then the so-called diamond window at more then 140 Km below the earth’s surface. 

The highly complex volcanics that solidify into kimberlite or lamproite are not the source of diamonds they are the elevator that brings them to the surface.  The volcanics rise through a complicated set of cracks and fissures until they near the surface where their extreme pressure causes them to blast an opening through the surface called a pipe.  In the case of kimberlites the pipe is carrot shaped, and in lamproites it is shaped like a champagne glass.

Cross section of a kimberlite chimney
By Heriberto Arribas Abato

Kimberlite and lamproite are similar magmas full of debris from the mantle of the earth as xenoliths with the actual magma acting as glue to stick the mass together.  Diamonds found in kimberlites or lamproites are part of the debris brought to the surface.  The magmas are rich in magnesium and volatile components such as water and carbon dioxide as these volatiles near the earth’s surface they explode into the characteristic carrot or champagne craters.  At the time of eruption they also form small conelike features on the surface of the earth that are quickly eroded away by the process of weathering.  Both types of eruption are quite rare and small in size.  They may also occur as dikes or sills in the country rock which undergoes considerable fracturing as the magma reaches towards the surface.  The rocks in the lithosphere are very brittle making it easy for kimberlites to reach the surface.

There are several different compositions related to kimberlites and they are named after the predominant mineral.  Normally the most abundant mineral associated with the primary magma is olivine making the kimberlite with olivine known as a periodotic kimberlite.  Other types are eclogitic, websteritic, sublithospheric and uncertain.  Any of these may contain diamonds.    

Mineralogical Association of Canada, Editor Lee A. Groat, Geology Of Gem Deposits, Short Course Series, Volume 37, Yukon Geological Survey, © 2007, Yellowknife, Northwest Territories
Gem Deposits,
Geology of Gem Deposits, Mineralogical Association of Canada, Editor Lee A. Groat,  Volume 37 © 2007
Industrial Minerals and Rocks, Page 418,,M1
Kimberlite, Wikipedia the free encyclopedia,
The Nature of diamonds, Kimberlites and Lamproites, American Museum of Natoual History,

Inclusions found in Diamonds tell quite a Tale

A flaw seen near the center of a diamond crystal - Wikipedia

The inclusions found in a natural diamond are a window on the interior of the earth.  Basically there are two types of inclusions found in a diamond.  The first type is a Syngenetic inclusion that was formed in the natural process of crystallization was ongoing.  The second type is the Epigenetic inclusion that was formed after the diamond was made.

The most serious flaw is a cleavage that can compromise the stability of a diamond.  These cleavage cracks are straight.  If they are serious enough they can split a diamond along the cleavage crack.  The diamond cutter often takes advantage of this flaw to cleave a diamond into two or more pieces.  They will also cause a diamond to split if accidentally subjected to a sudden high pressure event.

Bearding is hair-like cracks that often happen during the cutting of a diamond usually occurring around the girdle.  This is the area in the Anatomy of a Diamond where the setting prongs grasp the diamond.  Sometimes this flaw is also called “girdle fringes.”

Growth lines are sometimes called grain lines they typically form while the diamond crystal is growing.  If irregular crystallization occurs this is often a reason why these lines form.  If they are colorless they don’t affect the diamond’s clarity.  Sometimes though they are white or colored they are more visible and do affect the value of the diamond.

The next group of inclusions is man made that called ‘laser lines’ and can come from several different operations on the diamond.  The most common type is where the diamond cutter has used a laser for removing dark or prominent inclusions from the diamond.  The second most common is from the use of a microprobe used to analyze the tiny crystals of other minerals that are Syngenetic inclusions in the diamond. 

Feathers derive their name because they actually look like small feathers inside a diamond.  These seem to be Syngenetic tiny cracks that formed with the diamond.  Small feathers seem to be harmless, but if they reach the surface of the diamond crystal then can increase the risk of breakage. 

The last group of inclusions is definitely Syngenetic in nature; they are called pinpoints.  These are crystals of other minerals that were trapped inside the diamond crystal as it formed.  These are true windows into the interior of the earth as they were formed billions of years ago.  These same crystals are used by geochemists using a microprobe to determine their composition, and learn about the interior of the earth.  The most common inclusions are pyrope garnet, pyrite, zircon, eclogite and other rare minerals.  Sometimes an inclusion inside a diamond is what is termed a negative crystal which is just a void looking like a diamond crystal.  Other inclusions are minute drops of liquid usually water or liquid carbon dioxide.

Flaws are the characteristic inclusions found in a diamond.  They are called flaws because their presence means that the diamond is not perfect.  These inclusions act like fingerprints because no two of them are the same they are used to identify individual diamonds if they are lost or stolen.  Other inclusions affect a diamond’s clarity causing it to be less brilliant as they interfere with the light as it passes through a diamond.  There are other inclusions that can cause a diamond to fracture if it is subjected to a sudden sharp blow.


Mineralogical Association of Canada, Editor Lee A. Groat, Geology Of Gem Deposits, Short Course Series, Volume 37, Yukon Geological Survey, © 2007, Yellowknife, Northwest Territories
Gem Deposits,
Geology of Gem Deposits, Mineralogical Association of Canada, Editor Lee A. Groat,  Volume 37 © 2007
Industrial Minerals and Rocks, Page 418,,M1
Kimberlite, Wikipedia the free encyclopedia,

Wednesday, June 27, 2012

Finding Gemstone Deposits:

Ruby crystal on calcite
photo by Rob Lavinsky

Gems have been prized for thousands of years, for their color, luster, durability, hardness and their high intrinsic value per volume.  They are found in all kinds of geologic environments of all ages from thousands of million years to recent times.  Gemstones are also found in all kinds of rocks ranging from igneous to metamorphic to sedimentary and are classified according to the environment where they were formed.  The deposits are rare because of the geological conditions needed to form them are exceptional.  For example, in order for the Emerald to form the beryllium from which it is made has to come in contact with chromium or vanadium.  These elements travel in entirely different geochemical circles that are the exception rather than the rule.

It is important to realize that like any other commodity, gems are subject to the laws of supply and demand.  Even though the demand for gems remains about the same the supplies are becoming depleted.  Many of the gems especially the colored variety are mined in Third World countries by artesianal methods, i.e. by hand.  In any of these countries the discovery of the new deposit often leads to a local prosperity, but many of these stones become involved in the illegal trade that is being used to finance terrorism.

Sapphire crystal
Photo by Rob Lavinsky

These deposits of gemstones are volcanic in origin and are formed deep within the Earth’s crust.  Gemstones from this origin have formed over 100 Km below the surface and are brought to the surface as the result of magma intrusions or lava flows.  Diamonds are one type of this deposit that has formed from 100 to 150 Km below the surface.  These gemstones are found in potassium rich stone called “kimberlite” that is brought to the surface in an explosive eruption that proceeds at near supersonic speeds.  There seems to be a rule known as Clifford's rule that these eruptions take place in Achaean terranes or come up through younger terranes overlying Achaean terrenes.  Kimberlite is quite rich in peridot and appears to be full of xenoliths that are torn off the walls of the magma channel.  A cross-sectional view of the kimberlite is like looking at a carrot.  The stone itself is quite soft and easily eroded away with the diamonds being carried away with the rest of the erosion products.

Diamonds are not the only product that is found in a magmatic deposit so are others stones such as sapphires and zircons.  Sapphires are also formed under some very specific geological conditions the most important one is a magmatic stone that is low in primary silicates such as basalt.  The sapphires form as crystals in the basalt and they're released as products of erosion.  Although they form in the basalt they are rarely mined directly.  Zircons are another example of a gemstone that is found in a magmatic deposit.  Once again these gemstones are not mined directly from the stone that are found as the products of erosion.  In geology zircons are thought to be forever and the oldest dated minerals in the world are some zircons that were found in Western Australia that were dated at 4.5 billion years old.  Zircons are used by geochemists worldwide for dating formations of different ages, and are highly effective in this use.

Some other gemstone minerals that are found in magmatic deposits include:
Peridot, gem quality olivine usually found in mantle xenoliths.
Labradorite, found as gem quality grains in some basalts.
Zircon, found as crystals in granite, basalt and the rarer carbonatites.
Apatite, found as crystals in carbonatites.
Garnets, found as crystals in basalts as xenocrysts and granite.

Emerald crystal on calcite
Photo by Eva Krocher

Pegmatites are hydrothermal deposits contain more different types of gemstones in any other rock.  These are formed from the volatile rich fluids that are found in pegmatites when they are formed.  In some geological circles pegmatites are called “Giant granite” because they have the same minerals as granite except the crystals of the individual minerals are much larger.  There are two different kinds of pegmatites simple and complex; most of the valuable minerals are found in complex pegmatites.  Although many of these minerals could be classified as gems other minerals found in pegmatites are the ores for rare metals such as niobium or rare earths. 

Depending on the fluids present when the pegmatite is solidifying different gemstones are deposited.  If the fluid is rich in fluorine topaz will be deposited.  A beryllium rich fluid will produce the mineral beryl in its many forms ranging from aquamarine, emerald, morganite, or heliodor.  Lithium rich fluid is another possibility depositing spodumene or other lithium rich minerals.  Pollucite is deposited from a cesium rich fluid.  In some cases the fluid is rich in several different elements producing “Tourmaline” a gemstone that is actually rarer them diamonds.  A manganese rich fluid will cause spessertine garnet to be deposited.

There are specific zones in a pegmatite where gemstones are found.  Many of them are found in cavities called “Vugs.”  The crystals formed in this environment are usually clear and well formed.  A deposit of this nature containing red and green tourmaline was discovered in the 1970s at Newry, Maine that was worth more then $8 million from a single vug as large as a bedroom.

There are other hydrothermal environments that are also capable of producing gemstones ranging from volcanic rocks to sedimentary rocks.  This is where one is likely to encounter agates, petrified wood, opal, amethyst as well as a whole plethora of gems.  Turquoise is another mineral deposited by hydrothermal waters.  It is copper phosphate and its beautiful sky blue botryoidal masses have been admired for over two thousand years.

Metamorphic deposits:

Diamond crystal in matrix - USGS

The only gem minerals normally found in metamorphic rocks are garnet, zoisite (variety tanzanite), rubies and emeralds.  Rubies are the red variety of the mineral corundum that is aluminum oxide.  These gems are found in cordierite rich gneiss as well as marble.  Sometimes rubies are carried up from the depths of the earth as xenocrysts in basalt.  Most of the world's emeralds are found in low grade carbonaceous schist in ColombiaOther gemstones that occur in metamorphic rocks are iolite (the gem-quality lilac-purple variety of cordierite), titanite and kyanite.
Jade is another mineral that is found in high-pressure; low-pressure blue schist metamorphic rocks.  There are two entirely different minerals that are recognized as jade in the trade one of these as jadeite a compact variety of the mineral pyroxene, and the other is nephrite a compact variety of the mineral that is derived from tremolite.  Although these minerals are composed of common minerals it takes a very special environment for them to form.

Sedimentary deposits:

By far the most valuable gemstone found in sedimentary rock is precious opal.  The largest deposits of this mineral in the world are found in central Australia.  Other deposits are found in the United States and Mexico.  Most opal is found as a replacement for fossils.  Opal also occurs as replacement beds or blebs in sedimentary rock.  A good piece of opal showing good colors can be as expensive as a diamond.

Placer deposits:

In some placer deposits gemstones are relatively abundant particularly in areas where the local rocks are known to produce gemstones.  This is especially true in areas underlying by cordierite gneiss or marble.  Another area is where gemstone bearing pegmatites are abundant.  Because of their toughness and hardness gemstones that are eroded from their country rock tend to remain intact preserving the best gemstones.  The same rough and tough treatment these stones go under as a result of natural processes particularly running water the weaker and softer stones are broken up leaving behind the highest quality gemstones.  Most of the gemstones in the world are recovered from placer deposits.  In some cases the work of recovery can be quite primitive; in others the most modern technology and machinery is used.


Mineralogical Association of Canada, Editor Lee A. Groat, Geology Of Gem Deposits, Short Course Series, Volume 37, Yukon Geological Survey, © 2007, Yellowknife, Northwest Territories
Gem Deposits,
Geology of Gem Deposits, Mineralogical Association of Canada, Editor Lee A. Groat,  Volume 37 © 2007

Saturday, May 19, 2012

Minerals of Litchfield County, Connecticut

Platy ilmenite crystals encrusted on feldspar from Litchfield, Connecticut
Make an offer over $2,500
itchfield County, Connecticut has a very complex geology and a wide variety of minerals that ti date have been largely out of scope to the mineral collector.  It is our aim to make some of these minerals available to the collector.  Our first selection of minerals comes from a long abandoned mine in Litchfield , Connecticut that according to the records produced "soapstone" during the 1700s. Some of the minerals found at this locality include such world class specimens as kyanite, ilmenite, magnetite, quartz and many others.  There are over two-hundred minerals that have been identified in the county that was the home to over two-hundred mines in the past that have been long since abandoned and mainly forgotten.
James Dwight Dana in a painting by Danial Huntington - 1858

It is possible our long abandoned mine site is a Dana Locality because of some mineral specimens that were collected in Litchfield that are now in the collection of the Yale Peabody Museum in New Haven, Connecticut including ilmenite of which our locality still has world class specimens in sizes ranging from mere chips to boulders weighing up to several hundred pounds.  The size range of the specimens range from micro specimens to boulders that can be used in landscape arrangements.

We are making these specimens for sale to the mineral collector.  You can contact us at: for prices and additional information.

Below are illustrations of some of the specimens we have for sale:
This is a large specimen of staurolite in feldspar from Litchfield, Connecticut
Make an offer more then $150
Schorl wisps in quartz from the Whodunit Mine in Litchfield, CT
Price $25.00
Goethits pebble from an alluvial deposit in Salisbury, CT
Price $12,00
Stepped layers of ilmenite is feldspar from the Whodunit Mine in Litchfield, CT
Price $25.00
Platy ilmenite crystals in feldspar from the Whodunit Mine in Litchfield, CT
Price $50.00

This is a sample of kyanite from our locality in Litchfield, Connecticut.  This is a large specimen as can be seen by the quarter coin used to illustrate its size.  This specimen is truly spectacular with a mere photograph failing to do it justice.
Price $50

Blue kyanite in smoky quartz from the Whodunit Mine in Litchfield, CT
Price $45.00

About the Whodunit Mine we still don't know what they were mining except it is in a highly mineralised zone that contains many mineral specimens of all sizes and old artifacts.  

We will display more specimens that are for sale as they are prepared and photographed.

For further information about these specimens please contact us at

Saturday, March 10, 2012

Alabaster the Non-Gemstone

Church walls and gold leaf decorations made from calcitic alabaster in Poland
Photo by Beemwej

There are two distinct minerals that are called alabaster, one of them is calcium sulfate commonly called gypsum or anhydrite.  The other is a variety of calcium carbonate that is commonly known as limestone or marble.  Of these two the former is the alabaster of today, and the latter is the alabaster of the ancients.  Both of these materials are easy to work with, and have an attractive appearance making them favorites for small carvings and other works of art.

The formation of alabaster explained in Italian
by Miguel

Since we've already established that there are two different types of alabaster the best way to distinguish between them is by their relative hardness. The first type that is composed of gypsum is so soft you can scratch it would your fingernail because I have a Mohs hardness of 1.5 to 2. The calcite variety of alabaster is too hard to be scratched in this way having a Mohs hardness of 3 although you can scratch it with a knife blade. Because it is a carbonate it will effervesce when a drop of hydrochloric acid is placed on its surface. When the gypsum type of alabaster has a drop of mass placed on virtually nothing happens.

An alabaster lamp
Photo by David Dennis

Although alabaster can come in many different colors most people think of it as white, so much so that it has entered the language as a metonym for weight objects. In this sense it is often used to describe “alabaster skin” that means very light and quite transparent that is derived from the use of alabaster in building tombs.

Although alabaster is essentially too soft for use as a gemstone it often finds uses as a decorative stone for making different kinds of statuary and other objects de art. A very common use today is making the basis for electric lamps.

A piece of raw alabaster
Photo by Ra'ike

The word alabaster itself is derived from middle English as well as several other languages including Greek. The word was used to identify a type of vase made of alabaster. There is a certain amount of evidence that the word can be traced all the way back to ancient Egypt where it was named after the town Alabastron where it was commonly found. It was Alabastron where it was originally quarried, however the name of the mineral is still obscure.

The so-called “Oriental” alabaster was highly esteemed by sea ancients for making such items as small perfume bottles small point that basis that were called alabastra. This thing has also been suggested as a possible source of the mineral name. The craftsmen of this stone in ancient Egypt often used alabaster for use in candlestick chart and various other sacred and sepulchral objects. In the Sir John Soane’s Museum in London is a sarcophagus that was carved from a single block of translucent calcite alabaster that was mined Alabastron.

An alabaster carver at work.
Photo by Zyance

Both types of alabaster are essentially evaporative minerals in the case of the gypsum variety it is the mineral that evaporates from seawater before salt,  In the case of the calcitic variety is has its origin from the evaporation of lime water that has reached saturation.  Any further water loss causes the lime to come out of solution where it is deposited. A lot of this type of alabaster is found on the walls and floor of caves where it also forms the formations we call stalactites and stalagmites.

Ancient alabaster vases
Louvre Museum, Paris, France

Although most people think of alabaster as a white mineral it is also found in many other colors particularly when it is stained by mineral salts. Iron is the most common of these although copper and manganese also one of their own suite of colors to the stone. If you cut large blocks of this material into thin sheets they can be used as translucent windows such as those found in the Beineke Library of Rare Manuscripts and Books at Yale University. Throughout the ages how a master has been used to make many beautiful objects and will continue to do so into the future.

Thursday, March 8, 2012

Beryl the Genstone of Many Colors

Beryl crystals from Pakistan var. aquamarine
Photo by Gia Cassa

As a mineral beryl is beryllium aluminum cyclosilicate possessing the chemical formula Be3Al2(SiO3)6­.   As a gem it comes in many colors although pure beryl is colorless of the variety goshenite named after the town of Goshen in the central Berkshires of Massachusetts its type locality.  It is tinted by different colors causing it to be colored blue, green, red, yellow and white.  This is a mineral that is usually found in pegmatites although it is often found in biotite schists and in intruded limestone.  A rare occurrence is found in Utah called bixbite that has been colored red by manganese as an impurity.  Other gems in this family include aquamarine, emerald, green beryl, heliodor and morganite

An emerald crystal from Colombia
Photo by Gery Parent

Aquamarine is the color of sea water a bluish green with green beryl as a sub-order of aquamarine.  Emerald of course is bright green that is usually found in heavily intruded limestone although some occurrences are in biotite schist.  Heliodor is the yellow variety of beryl that is sometimes galled “golden beryl.”  Morganite is sometimes found associated with both aquamarine and golden beryl, bit is differentiated by its pink color.  Red beryl is also called bixbite or red emerald because of its red coloration.  Of all the beryl’s bixbite is the rarest, but only occurs in small crystals allowing gems cut from it to be lass then 5 carets in weight,

Golden beryl or heliodor

Beryl aside from its use as a gem is also the ore of beryllium where it occurs in granitic pegmatites.  One such crystal was a giant that occurred in the Bumpus Quarry in Albany, Maine that was about 5.5 meters long by 1.2 meters in diameter that weighed around 18 metric tons.  The largest crystal of any kind of mineral was found in Madagascar is a beryl crystal that was 18 meters long by 3.5 meters in diameter.  That is the size as the boiler on a steam locomotive.

A crystal of red beryl var. bixbite from Utah
Photo by Rob Lavinsky

Beryl is found on all the continents wherever crystalline igneous or metamorphic rocks are found.  The gems are found in the core of pegmatites where at times terminated crystals are found growing into cavities or vugs in the rock.  Some beryl like the emeralds found in Columbia are found in a peculiar black limestone that has been intruded with granite that contain in addition to the beryl an abundant amount of pyrite that certainly predates the formation of the emerald crystals.. Beryl is also found associated with biotite schist.   Many of the emeralds found in the Ural Mountains of Russia are this type of deposit.  The emeralds found at the Crabtree Corners deposit in North Carolina are also an example of this kind of deposit.

A crystal of morganite on albite and quartz.
Photo by Rob Lavinsky

One of the most important deposits of aquamarine in the United States is found in the Maryall district of New Milford, Connecticut where they occur in a large pegmatite that that was originally mined for feldspar and mica.  This mine has produced some fine specimens of both aquamarine and heliodor beryl including a 44 carat heart on display in the American Museum of Natural History in New York City.  It is also known to produce many other minerals especially large garnets and uranium minerals.