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.

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.

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

How to turn silica into agates

A Lake Superior agate ground into a sphere.
Photo by Fluorite

Of all the gems in the world agates are one of the most complicated even though they are formed from silica one of the most abundant compounds on earth.  According to Peter Heaney of Penn State University Agates are really complicated stuff whose composition has remained a mystery for many years.  It is only with the application of modern high-tech methods has the makeup of this really complicated mineral been understood.

Agate is composed of what is termed crypto-crystalline silica, or silicon dioxide (SiO₂) that forms long thin fibers of silica that is more a polymer then a crystalline substance.  The real secret of forming an agate Heaney feels about how silica dissolves in water his research came from a need to discover how agate was being deposited in the pipes of geothermal power plants.  Silica kept coming out of solution and was clogging the plants with agate.  His problem was how to keep the dissolved silica from sticking to the insides of the pipes.  The question really was; how do you stop an agate from growing.

A slab of blue agate with a quartz crystal center.
Photo by Tomomarusan 

Because of a line of research I undertook on the formation of geopolymers that makes use of sodium silicate, sodium hydroxide and some sort of pozzalan material to form a similar compound to agates that is used as a green alternative to concrete.  This line of research gives me a useful insight on the formation of agates.  The hot water found deep in the earth contains a lot of dissolved silica that is brought to the surface naturally by hot springs and geysers.

Most agates are found in cavities in basalt or similar magma where it fills the cavities.  Other places where agate forms is in places where it replaces other minerals or fossils.  Petrified wood is one example in other cases it can be petrified bone or even coral as in Florida.   

One of the many forms agate rough can assume.
Photo by Rob Lavinsky

According to the theory an agate tarts with a cavity in a rock with the best being found in basalt. All volcanic rocks that get up to the surface where they harden contain a lot of water and carbon dioxide that will bubble up just like seltzer water. The rocks are full of holes similar to the pipes in the geothermal generating plant. In this case however it is these holes in the rock that fill with the silica solution that become agates. The silica bearing water does not all enter the cavity at the same time causing bands to be formed in the agate. Not only does the silica bearing solution form thee agate and also bears other minerals principally iron or manganese oxide that causes the different colors that are seen in the agate. These solutions percolate through the rock, and the minerals they contain begin to crystallize.

A Lake Superior agate note the banding.
Photo by Iowagateman.

By studying agates with transmission electron microscopy, and by x-ray diffraction and has been found that about 90% of an agate is quartz however there is another mineral and has the same composition but a different structure that is called mogenite. This mineral is more like carbon that can crystallize in either graphite or diamonds. 90% of an agate is quartz the remaining 10% is moganite that is an important factor in the formation of agates.

What an agate is examined under light microscope it displays a layer of fibers crystals that nucleated on the wall and radiate inward into the cavity just like the spokes of a bicycle wheel. Usually the first layer inside the cavity is a very fine material called chalcedony that is a mixture of quartz and moganite. Next in the sequence is a coarse band of quartz crystals that is pure quartz with no moganite.

One of the first questions asked about a maggot is why do we see these two different layers? They are both the same, silicon dioxide, but what is changing the crystal structure of them?

Another curious thing about agate fibers is they twist in growing a helical fashion.

To compound the mystery is the crystallographic direction in which the fibers grow with in bands that favors growing perpendicular to the normal growth direction.

Theoretically what happens is this that causes the characteristic banding seen in an agate with the colors coming from trace elements in the solution like iron and manganese. The agate itself is like a Russian doll having a hierarchical layering very similar to some kind of life form. This may be caused because chemically silicon is very similar to carbon.

Suppose the silica bearing water flowing into the cavity was only a little bit polymerized its precipitates onto the wall. If the concentration of silica gets high enough that polymerizes in short but repeat units of 5 to 10 molecules. It has been theorized that these polymerized molecules get pulled out of solution very quickly and become crystallized very rapidly. Because this happened so quickly any mistakes are made in the crystal structure causing weird minerals to form like moganite.

Under normal conditions all you will see are quartz crystals, but this is the process that proceed slowly. Many times this causes the center of the agate to appear as a geode line with quartz crystals and the rim of the cavity to be deposited as chalcedony. Although the deposits of moganite can proceed rapidly the quartz crystals themselves are deposited quite slowly. If one were to take a glass of water saturated with silica it would take two years before even the tiniest quartz crystals were deposited.

There are also channels that are located between the crystal fibers that work by attraction to pull water into the center of the cavity; thus you have a continuous supply of water feeding into the system that contains silica. The silica will polymerize again when it approaches saturation causing a layer of moganite to crystallize rapidly inside the cavity. This is quite an agate that has its banding pattern. However, this has not been proven experimentally.

One of the things we are certain of whatever is that agates form close to the surface of the earth at low pressures and temperatures where they are found in volcanic rocks, but also as replacements and many other environments. Agates are very resistant to erosion and are often found as just a roundish lump with a rough coating just laying on the surface of the ground waiting to be picked up, cut and polished that can be used in a piece of jewelry.