A translucent quartz with sparkling reflections. It occurs in a range of colors.
What is Aventurine?
Aventurine is a variety of translucent quartz with abundant small plate- or flake-shaped inclusions. Light entering the quartz strikes these inclusions and reflects from them. This produces a sparkly appearance known as "aventurescence."
When the inclusions are abundant and in a common orientation, their reflections can be eye-catching. This property, along with desirable colors, are what give aventurine its appeal as a gemstone. Aventurine is usually green, but also occurs in orange, yellow, red, pink, brown, white, gray, and blue.
Spelling Note: Aventurine is spelled with a "v" as the second letter. Speak and write carefully to help others know that the word does not have a "d."
Types of Inclusions
The most common inclusion in aventurine is fuchsite, a green chromium-rich mica. It can be abundant enough in the quartz to give the material a green color. Some people think that aventurine should be classified as a rock because the inclusions often make up ten to twenty percent of the material.
Small reflective particles of other materials can cause aventurescence in quartz. Hematite and goethite can produce pink, orange, red, and brown aventurine. Muscovite and ilmenite can produce blue, gray, or white aventurine. Bright reflections and attractive colors make aventurine a popular semiprecious gemstone.
Sources of Aventurine
Small amounts of aventurine occur in many parts of the world. India is by far the most important commercial producer of aventurine. Brazil is the second-place producer. Russia, Spain, Austria, and Tanzania produce smaller amounts of aventurine.
Some people hold the opinion that most of the material sold today as "aventurine" has inadequate aventurescence to merit the name. Immediately discernable aventurescence in quartz is hard to find, and remarkable aventurescence is extremely rare.
Physical Properties of Aventurine
|Chemical Classification||Silicate - SiO2|
|Color||Usually green. Also orange, yellow, red, pink, white, brown, and blue.|
|Streak||Colorless (harder than the streak plate).|
|Diaphaneity||Translucent to nearly opaque.|
|Cleavage||None, conchoidal fracture.|
|Mohs Hardness||6.5 to 7|
|Specific Gravity||2.6 to 2.7 (higher when heavily included)|
|Diagnostic Properties||Aventurescence, usually green, hardness, conchoidal fracture.|
|Uses||Gemstone, small sculptures, utility items.|
Physical Properties of Aventurine
Aventurine has most of the properties of quartz, its dominant ingredient. The presence of inclusions gives the quartz its aventurescence and alters some of its other properties.
Aventurine has a hardness of about 6 1/2 instead of the 7 of quartz. The most common mineral inclusions associated with aventurine all have a hardness lower than quartz. This is thought to weaken the material and result in a slightly lower hardness.
Many of the common aventurine inclusions have a specific gravity that is higher than quartz. If abundant, inclusions such as hematite, ilmenite, and goethite should give aventurine a specific gravity that is slightly higher than quartz.
Uses of Aventurine
Green aventurine is a common material used to produce beads and cabochons. These are used to make earrings, pendants, rings, and other jewelry. Other colors of aventurine are used to produce these items, but they are seen less often because nice aventurine in those colors is rare.
Aventurine is sometimes used to make bowls, vases, and small sculptures. Green aventurine is a less expensive and popular alternative for jade and amazonite. Some buyers simply want an attractive green stone, and the flash of aventurine suits them.
Aventurine as Tumbled Stones
Aventurine is an inexpensive and popular material for making tumbled stones in a rock tumbler. If the mica particles are small, a smooth and lustrous finish can be produced. Coarse mica particles tend to pluck out, giving the polished stones a pitted appearance. Aluminum oxide, cerium oxide, and tin oxide will all produce a bright polish on aventurine.
Aventurine and translucent quartz without aventurescence are often dyed bright colors. This is used to produce low-cost cabochons with bright colors that are often seen in inexpensive jewelry. The name "aventurine" is inappropriate but is used for its greater appeal when compared to "translucent quartz" or other appropriate names.
More About Aventurescence
The phenomenon of aventurescence is the glittering appearance produced by light entering a stone and reflecting from small reflective grains of metal or mineral. This phenomenon is not confined to quartz.
Oligoclase and plagioclase feldspars sometimes contain inclusions of hematite or copper that produce an aventurescent luster. These are known as "aventurescent feldspars" or by the more popular name "sunstone."
A few lava flows in Oregon contain vugs that host small feldspar crystals. These crystals sometimes contain suspended flakes of copper or other minerals and display aventurescence under direct light. These feldspars, aventurescent or not, are all called "Oregon Sunstone." The gem material ranges in color from very pale yellow to orange to red. Some blue, green, and color-zoned crystals are also found. Aventurescent pieces are cut into cabochons, and some of the finest aventurescent pieces are cut into faceted stones. Pieces with perfect clarity are faceted. Oregon Sunstone is very popular with people who live in these areas and tourists who visit.
Aventurescent iolite is also known. Transparent blue iolite with inclusions of hematite platelets, mica, and other materials are known from locations in India and Tanzania. These are often sold under the misnomer "iolite sunstone."
"Goldstone" and "Aventurescent Glass"
The name "aventurine" originated in the 1600s when Italian glass makers accidentally blended tiny flakes of copper into a batch of molten glass. The result was a sparkly glass that they named "avventura" or, in English, "by chance." It was beautiful. Soon they were using it to make a variety of products, and the name "aventurine" began to spread.
Similar glasses are still made today. They are known as "aventurine glass." The most popular of these glasses is a simulant of aventurine known as "goldstone." Goldstone is easy to recognize because the metal flakes within the glass are such strong reflectors of light. The typical product is a clear glass with copper flakes, but sometimes blue or green "goldstone" is made by using colored glass instead of clear. Goldstone is a popular material for producing cabochons and other jewelry items.
|Ruby and Sapphire|
|Gemstones of the World|
|Pictures of Opal|
More From Geology.com: