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PHYSICAL PROPERTIES:
Chemistry: SiO2 colored green by
fuchsite mica: K(Al,Cr)2AlSi3O10(OH)2
Composition: Mica Included Quartzite
Color:Green, blue, peach
Class: tectosilicate
Crystal system: Hexagonal-R; 32
(trigonal-trapezohedral)
Crystal habit: massive aggregate
of interlocking quartz grains
Fracture: conchoidal
Hardness: 7
Specific gravity: 2.64 to 2.69
Refractive Index: 1.55
Luster: dull vitreous
Streak: white
Cleavage: none
Transparency: opaque

COMPOSITION & ENVIRONMENT:
Green Aventurine Quartz, is actually a quartzite. Which is a rock, not a mineral.
It is composed essentially of interlocking macrocrystalline quartz grains and other color imparting minerals. Usually formed by metamorphism (metamorphism is the alteration of a rock due to changes in heat, pressure or chemical environment.) When a quartz rich sedimentary deposit or a sandstone undergoes metamorphism the original material alters to a compact rock. Composed of interlocking quartz grains known as quartzite. Most of the aventurine quartz is filled with tiny platelets of a green chromium mica, called fuchsite. Although some aventurines contain different varieties of mica, hematite or other sparkly inclusions. These colorful specks add sparkle and also create or help create the body color of the aventurine they inhabit.

DISTINGUISHING CHARACTERISTICS:
As you move a piece of aventurine. The sparkling inclusions produce reflections causing a glittering effect. In the gem trade this effect is known as aventurescence. Over the centuries other gems and even types of man made glass have been called Aventurine. An explanation for the name aventurine comes from the 1700's. A similar looking man made glass called Goldstone, was reported to be discovered by chance. In Italian, the words (a ventura) mean, by chance. Hence the term aventurine. Two different feldspar gems, both typically a goldish reddish color. Have also been associated with the term aventurine. All of the materials called aventurine are filled with small lustrous specks that reflect light. What those specks are, depends on which aventurine you’re talking about. Goldstone is filled with tiny metallic copper crystals. One of the sunstones, the labradorite feldspar, is filled with tiny copper crystals that have exsolved (separated out of the crystal lattice). The other sunstone, an oligoclase feldspar, is filled with tiny crystals of exsolved hematite, which produce reddish inclusions.

LOCALITIES:
Deposits are found in Brazil, India, Austria, Russia, and Tanzania. India produces the majority of the world’s aventurine quartz. Most of which is a greenish color. The best green aventurine comes from the region of Bellary. A town in the state of Mysore in south central India, 270 miles northwest of Madras. Besides the material from India. Green Aventurine Quartz may also come from Brazil, Madagascar and several other occurrences of good green material are found around the world, including the United States. Some of the nicest sunstone verity comes from the state of Oregon. In Czarist times, Siberia produced some of the finest aventurine, found in the Korgon Mountains of Tomsk Province. There is also some new Russian aventurine on the market since the fall of the Soviet Union. Aventurine quartz of redish brown, or an orange-yellow are also widespread. But these are seldom as striking as the green. These other colors are generally due to the flakes of mica being stained by iron oxides or hydroxides.
Sometimes the flakes are hematite rather than mica.

USES:
All of the above aventurines are more or less only used as lapidary materials. Whether it be the attractive natural greens, blues or peach colors. Found in the more recognized quartzite verities of aventurine. Or the shimmering copper colors found in sunstone and goldstone. Very fine grades of Green aventurine that show little, if any, of the sparkling impurities. Has been miscalled Indian jade. It is usually pretty easy to tell the difference just look into the stone with a 10 power hand lens and see if you can see the very small mica flecks. Sometimes the flecks are so small that other gemological instruments are needed. These grades are probably as rare if not more rare than the jade they mimic. Probably not something to worry about too much.

FACTS & HISTORY:
The astrological sign of green aventurine quartz is Aries. Green aventurine quartz can be an alternate birthstone for the month of August.

Records from the late 1800's show that aventurine was being imported to the German gemstone center of Idar-Oberstein. After World War I, these lapidaries were importing the material in quantity and are still doing so today. American dealers have been importing it since World War II. Today a good deal of aventurine quartz is sold as beads.

One of the most impressive examples of cut aventurine is an obelisk carved by HelmutWolf. A famous carver from the village of Kirschweiler near Idar-Oberstein. It stands 5-1/2 feet high and weighs 2.5 tons. It was cut from fine green Indian Aventurine.

It is suspected that aventurine is the only gemstone in which the man made gem was know before it's natural counterpart.

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