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Tuesday, February 28, 2012

The Emerald Green Garnet Andradite

Demantoid an emerald green variety of andradite garnet on a matrix of serpentine,
Photo by Rob Lavinsky

Andradite is another species longing for the garnet family that is classified as a nesonsilicate with a formula approximating Ca3Fe2Si3O12­.  This family of garnets includes three different varieties they come in various colors. There is one variety where titanium ions substitute in the formula producing a black stone that in the gem trade is called melanite, or is sometimes referred to as titanian andradite. The second stone in this group is referred to as the demantoid garnet that is found ophiolite deposits where it is associated with chromium. The stones are often the vivid green in color that occur in small crystals rarely over one carat in size. Because of their rarity they are often worth more than $1000 per carat in the world. The third type of stone in this family is called Topazolite that is yellowish green in color and is sometimes found in a high enough quality so they can be cut into faceted gems.

Melanite garnet crystals
Photo by Rob Lavinsky

This garnet occurs in skarns in impure limestone that has been intruded by igneous rock. Sometimes it is also found in calcium rich igneous rocks. Probably the most common place to find andradite is in a rock called serpentine that also produces asbestos. Andradite garnets have been found in the asbestos mines around Thetford Mines, Quebec in small crystals. Serpentine is thought by geologists to be metamorphosed oceanic crust that was caught up in a mountain building event where some of the ocean crust was incorporated into a continental landmass.

Topazolite crystals
Photo by Rob Lavinsky

There are several other minerals that are commonly associated with andradite including this vesuvianite, chlorite, epidote, spinel, calcite, dolomite and magnetite. One of the varieties of andradite is often found near iron mines where the over is magnetite. It is found as braunite on the rock dumps at the old Tillie Foster iron mine in Brewster, New York.

A faceting grade crystal of demantoid.  Sometimes faceted gems cut from this stone can sell for well over $1,000 per carat.  Most of these stones are small rare;y affording faceted gems weighing much more then a carat.
Photo by Rob Lavinsky

Andradite is found in Italy around the area of Mt. Vesuvius and other volcanic areas that are underlain by limestone.  It is also found in Russia in the Urals.  In the United States this stone is found in Arizona and California.  On the East Coast several occurrences are in the Danbury, Connecticut area where andradite occurs in limestone deposits along Rt. 7 where the limestone is in close proximity to intrusions of granite where it is associated with danburite and idocrase.  This is a mineral that should be found in serpentine or contact altered limestone anywhere they are found.

Amber is Fossilized Tree Resin

Amber with a spider inclusion that came from the Baltic Sea area.
Photo by Elizabeth from Holland 

Although not a gemstone in the proper sense Amber in reality is fossilized tree resin that is several million years old. It is one of the oldest gems known to man where it is mentioned in the Bible and also by Pliny the Elder, who lived during the Roman Empire. Pliny was killed by the eruption of Vesuvius on August 24, 79 A.D.

Although amber is found in many parts of the world its earliest occurrence was when Amber was found around the Baltic Sea where it is still mined to this day.  Other places in the world where amber is found include the United States, the Dominican Republic, New Zealand and Indonesia.  In truth amber enjoys a worldwide occurrence.

Blue amber from the Dominican Republic
Photo by Vassil 

Mankind has admired amber for thousands of years where he appreciated its color and natural beauty since Neolithic times.  Amber is still used as an ingredient in perfumes; it has also been used as a healing agent in folk medicine.  Amber however finds its major use in Jewelry.

Amber pendents with inclusions
Photo by Adrian Pingstone

Geologically there are five recognized classes of amber that are defined according to their chemical composition.  Amber comes from a sticky tree resin that over time hardens by the loss of volatile chemicals it can contain various animal and plant remains as inclusions.  Some amber occurs in coal seams that are called resinite.  The term ambrite is specifically applied to amber that found in the coal seams of New Zealand.

Amber rough from the Baltic Sea where it is washed up after heavy storms.
This amber is waiting to be processed.
Photo by Lanzi

One of the rarest members of the amber family is found in the Dominican Republic that is blue and flouresis under ultraviolet light.  Amber is found in several parts of the eastern United States most notably on Martha’s Vineyard where it is found on Gayhead.  The stone is also found in the marl deposits of New Jersey.  

Monday, February 27, 2012

Ametrine the Astounding Bicolored Stone

A faceted example of ametrine
Photo by De Wela49

Ametrine is a variety of colored quartz where one end of the crystal is amethyst colored and the other end is citrine colored. Most of these stones are found in Bolivia and are often marketed under the name bolivinite. Because they are fairly abundant they are not considered to be an expensive gem. Many of these stones today are actually synthetics made in Russia.

In 1994 a Russian chemist perfected a method to make multicolored quartz crystals in a pressurized vessel. These stones are later subjected to radiation that brings out the typical Ametrine colors. It is easy to detect these stones because in nature neither yellow-green nor gold-blue exists. In nature but artificial ametrine can also be created by treating an amethyst crystal on one end with heat. Since quartz is a poor conductor of heat only one end of the crystal that has been heated will change color.

An example of ametrine from Bolivia.
Photo by Ra'ike 

The most probable cause of a bi-colored amethyst crystal is by differential heat that is applied to one end of the crystal; in the case of Bolivianite causing a temperature differential across the length of the crystal will create a bi-colored stone.

Most of the Ametrine enters into trade comes from a single mine in Bolivia although there are some other places that produce the same gem notably Brazil and India. There are several legends concerning the Bolivian mine the most prevalent being the one about a Spanish Conquistador who presented them to the Spanish Queen as a present after he had learned about the Anahi mine where they were produced as a dowry present to Mary by an Indian princess named Anahi from the Ayereos tribe.

An ametrine crystal also from Bolivia
Photo by Rob Lavinsky

Typically Ametrine is faceted into a rectangular shape with a 50-50 combination of amethyst and citrine showing its bicolor nature. There are times when there is a checkerboard pattern of facets that is added to the top of the stone to increase the natural light reflection. This stone can also be cut in such a way as to blend the two colors creating a mixture of yellow, purple, and peach tones in the stone. Ametrine is also a popular stone among artistic cutters and carvers that like to play with the various colors creating landscapes from the stone.

When buying one of these stones the buyer has to remember that at a Moh’s hardness of 7 it is not a particularly durable stone that should not be used in rings that are going to be worn steadily. This tone is more suitable for broaches and pendants. You can buy this stone in just about any size or shape but remember the color contrast stands out better in stones over seven carats in size.

Saturday, February 25, 2012

Amazonite the Green Feldspar Gem

Amazonite a green variety of microcline feldspar.
Photo by Rob Lavinsky

Amazonite that is also cold Amazon stone is a green colored variety of microcline a type of feldspar. It got its name from the Amazon River when certain green stones were formerly obtained from the land surrounding the river although it is doubtful that any of this green feldspar occurs anywhere in the Amazon region.

Amazonite with terminated smoky quartz crystals.
Photo by Rob Lavinsky

Although amazonite is a mineral having a limited occurrence it was originally obtained from the Miass district in the Ilman Mountains about 50 miles southwest of Chelyabinsk, Russia. It was found here in granitic rocks in small quantities. It can also be found in the United States as high-quality crystals found in the area of Pike's Peak, Colorado. Some spectacular specimens displaying amazonite along with smoky quartz crystals in a matrix of albite and orthoclase feldspar have been found around Pike’s Peak. Another area where amazonite is found in Colorado is at Crystal Peak in El Paso County. There are other places in the United States were amazonite has been found associated with pegmatites like it is in Colorado.

Amazonite cut in cabochon.
Photo by Eurico Zimbres

For many years many people assumed that the bright green color of amazonite was because of copper compounds that are often similarly colored having bright blue or green colors. Recent studies that have been undertaken suggest that the blue-green colors of amazonite are actually caused by a small amount of lead and water as crystal defects in the feldspar.

A lapis lazuli pectoral made in Ancient Egypt.  A small piece of amazonite can be seen as the round stone at the bottom of the pectoral.
Photo by Henryk Jan Dominiak 

Amazonite has been used for years when it has been cut and polished as a gemstone, but as gem it is not advisable to use this in the rings because it is brittle and fractures is easily.  However, when cut en cabochon is readily finds use in pendants and lockets.  Large masses of this stone are used for carving.

Friday, February 24, 2012

Apatite as a gemstone

A crystal of gemmy apatite on a matrix of quartz.
Photo by Rob Lavinsky

Apatite is a whole family of minerals some of them are gems, but the place where you are most familiar with is your teeth and skeleton that are composed of hydroxalapatite.  Basically apatite is composed of calcium phosphate with extra ions added to its crystalline structure to cause it to be known as several related names: flourapatite, chlorapatite, bromapatite and in the case of your bones the OH ion. Apatite is used as the defining mineral for number five on the Moh’s hardness scale. Hydroxyapatite is a relatively rare form of the mineral are mostly groups are absent or contain many carbonate and acid phosphate substitutes that form a large part of bone material.

A twinned crystal of Apatite
Photo by Rob Lavinsky

Flourapatite is much more resistant to acid attack than hydroxyapatite it is for this reason that fluorine is added to your drinking water and can also be found in your toothpaste. In the case of the fluoridated water it allows the interchange of fluoride ions that substitute for hydroxyapatite ions. If you get too much fluoride into your system it can result in dental or skeletal flouresis.

Fission tracks are used by geochemists and geophysicists for determining the thermal history of orogenic belts and settlements in sedimentary basins. This is because as a trace element uranium and thorium are found in crystalline apatite. The same phenomenon is also used in paleontology to establish the dates of prehistoric wildfires.

A faceted gemstone of apatite.
Photo by Rob Lavinsky

Apatite in phosphorite is a phosphorus rich sedimentary rock containing between 18 and 40% of phosphorus pentoxide (P2O5). A great deal of the phosphorite is mined in central Florida in an area that is called “Bone Valley” for use as fertilizer. It contains so much uranium that during the Cold War if supplied several thousand tons of yellowcake uranium to the Atomic Energy Commission. The piles of mine slimes resulting from mining and refining this phosphorite presents a serious environmental hazard not only from the uranium, but also from the contained fluorides. The apatite contained in phosphorite is in crypto- crystalline masses that are called colophane. Apatite is also mined from igneous rocks in the Kola Peninsula of northeast Russia as a fertilizer as well..

Clear crystals of apatite can be faceted creating an extremely handsome gem. Because of the sensitivity to heat and shock gems that are cut from apatite are never heat-treated to improve their looks. Although apatite is found all over the world most of it is small crystals disseminated through the rocks; larger crystals are quite rare. Most of the faceting grade apatite crystals are shades of blue, although some are blue-green.

A thin section of hornblende and apatite
Photo by Pitor Sosnowski

Most of this faceting material is found in metamorphosed limestone that is commonly called marble. In general the more impurities that are found in limestone the more apt it is to produce apatite when it is metamorphosed. There is a bed of metamorphosed limestone that reaches all the way from Québec to Alabama just of the West of the Precambrian core of the Appalachians. In many places this is called the Great Valley of the Appalachians but the same marble belt extends all the way to Canada. There is apatite found throughout this entire region, and others like it all over the world.

Thursday, February 23, 2012

Almandine Garnets

A cluster of almandine garnets in matrix.
Photo by Rock Currier
Almandine is a member of the garnet family that was known to the ancient Romans where it was pronounced “alabandicus” where it was known to Pliny the Elder. This was a stone that was either found near or worked at the town of Alabanda a town in Cariua in Asia Minor. In composition it is an iron aluminum garnet possessing a deep red color that inclines toward purple. Almandine as a stone entering the jewelry trade is either faceted or cut with a convex face en cabochon when it is then called a carbuncle. When the stone was viewed through a spectroscope in a strong light, it generally shows that has three characteristic absorption bands.

The stone is one end member of a solid solution series the other end up being the pyrope garnet that is magnesium rich rather than iron. The chemical formula for almandine garnets is: Fe3Al2Si3O12. The solid solution occurs when magnesium substitutes for the iron causing an increasingly rich pyrope composition. Almandine is the ferrous iron member of the class of garnet minerals that are important group of rock forming silicates that are the main rock forming minerals in the Earth's crust. Crystals of almandine are often seen in mica schist fillet very much like raisins in a pudding. This type of garnet crystallizes in the cubic space group Ia3d having a that a cell parameter of 11.512 Å at 100° Kelvin.

A gemmy red almandine garnet on a matrix of mica schist
Photo by Rob Lavinsky

Almandine can be found rather abundantly in gem gravels found in Sri_Lanka, but are actually pretty abundant in any stream gravel that is found adjacent to metamorphic or igneous rock. In this case almandine garnets are a constituent of the black sand that are classified as stream heavies. Sometimes almandine garnets are so abundant on beaches that they are mind commercially for their abrasive qualities.

In the gem trade almandine garnets have gone by many names among them are Ceylon ruby. If their color takes a violet tint the stone is sometimes called a Syrian Garnet. Large deposits of some especially fine album being garnets were found in the Northern Territory of Australia that were marketed for years as Australian rubies. An especially interesting variety of the stone that is found in stream gravel's in parts of Idaho show a star when they are cut, and marketed as star garnets.

A collection of jewlery in Kracow, Poland made from pearls, diamonds, almandine garnet and enamel.
Photo by S.F. Burgerer

As a mineral almandine is widely distributed throughout the world with fine rhombic crystals that are called to dodecahedra that are found in the schistose rocks wherever crystalline bedrock is found. In

One of the best localities in the United States is located at Gore Mountain in the Adirondack mountains of New York State at the town of North Creek. Some of the crystals that are found enclosed in gabbro are more than a meter across they are mined by the Gore Mountain mining company that crushes them for abrasives. Many of these garnets from this particular deposit are faceting grade and makes an extremely attractive gems.

Monday, February 20, 2012

Aquamarine as a Gemstone

Aquamarine is a member of the beryl family of gemstones that is usually colored various shades of blue/green or may appear as either light green or even as dark blue stones rivaling sapphire in color.  The mineral is a beryllium aluminum cyclosilicate with the formula Be3Al2(SiO3)6Terminated crystals of beryl are relatively rare, but are known to occur.  The stone has a value as a gemstone, and is a common ore of the metal beryllium.  In the case of aquamarine a small amount of iron that causes crystal defects in the crystal is the cause of its color.  The mineral beryl because of impurities in the crystal does occur in several different colors including green blue, yellow, red and white.

Aquamarine in a matrix of feldspar crystals.and other minerals including schorl the black crystal in the middle of the specimen.
Photo by Rob Lavinsky

The colors of aquamarine can range from light blue like that of the sky to a deep blue of the sea.  The darker the color the higher the price some aquamarines can sell for as much as $2,000 per caret although lighter stones only fetch a few dollars per carat.  The stone itself is fascinatingly beautiful with much appeal to women all over the world because it can complement or eye color.  For creative gemstone cutters it is an inspiration because of its ability to be cut in so many designs and still keep its beauty.

A water etched crystal of aquamarine from Brazil
Photo by Rob Lavinsky

Aquamarine is epitomized by its blue color, and the deeper blue the color the more expensive the stone making it one of the most popular stones rivaling at times its more expensive cousin emerald that also belongs to the beryl family.  The stone is hard enough at Mohs hardness of 7.5 to 8 so it can be used in most types of jewelry making it almost as popular as the classic stones emerald, ruby and sapphire.  In reality aquamarine is related to the emerald, but unlike its more famous cousin it usually free of flaws.  One flaw that is sometimes seen in aquamarine is long thin tubes that sometimes lend to its beauty in the form of chatoyancy forming tiger eyes or more rarely a star stone much like star sapphire.  Both forms of the stone command very high prices.

An example of a pear shaped aquamarine faceted gem.
Photographer Unknown

The color of aquamarine is caused by ions of iron causing crystal defects in the mineral beryl that is normally clear that is called goshenite my mineralogists because its type locality is in Goshen, Massachusetts were it is found in lithium bearing pegmatites.  Aquamarine can range from a pale blue to a strongly colored sea blue.  In some aquamarines you can see a light greenish simmer that is a typical feature of the stone.  Thee most prized color however is a pure clear blue transparent stone bringing out the transparency and shine of this magnificent stone.

Friday, February 17, 2012

The Royal Purple Stone Amethyst

At one time the amethyst was considered to be a precious stone and was even found among the crown jewels of France. This particular stone came from the basalt outcrops along the Bay of Fundy near Parsboro, Nova Scotia.

The French Crown Jewels that are kept in the Louvre

Amethyst is a form of quartz that has a hardness of seven making it suitable for jewelry and when cut it takes a very high polish.

An amethyst crystal from Brazil

Among the many forms of crystals that it takes is one special type called scepter crystals that form with a narrow bottom that widens at the top.

A scepter crystal of amethyst.

A common form for amethyst to take is the lining of the geode. The best place in the world to find these amethyst geodes is in the basalt flows of Uruguay that formed as bubbles in the basalt as it was cooling.

An amethyst filled geode from Uruguay.  In this case the crystals form a druse inside a bubble formed in basalt.  Note the green iron staining in the outside of the geode.  The geodes are eroded from the basalt flow and are found lying on the soil.
Photo by Didier Descouens

At other times it is just found cavity.     

This is a druse of amethyst found in a small geode.

When amethyst is cut the stone was usually faceted one of forms it takes is an emerald cut although there are many other types of faceted stones that it can take.

An emerald cut amethyst

Some amethyst is cut in the intaglio style something like a cameo only the surface of the stone has the design incised.

An intaglio cut amethyst.

For centuries amethyst is then used in jewelry as a faceted stone or en cabochon. It

A ring with an amethyst stone.

Sometimes amethyst if the crystal is large enough is carved in the statues. The Chinese are particularly adept at this artform.

an antique vase made in the 1600s containing many different stones including amethyst.

Photos from Wikimedia Commons

Thursday, February 9, 2012

Announcing a new beryl locality in South America

Nick's blue aquamarine
Photo by Nick

We just made a major find of beryl gemstones in South America.  So far the locality has produced translucent rough capable of making the most beautiful blue cabochons you have ever seen.  The rough was removed from a single crystal several meters long is a beautiful blue resembling some turquoise.  We haven’t priced this rough while we are evaluating it, but you can get further information as soon as we develop it from John Carter at: