Aventurine

Aventurine is a form of quartzite, characterised by its translucency and the presence of platy mineral inclusions that give it a shimmering or glistening effect termed aventurescence.

Etymology and history

The abbreviation "aventurine" originally applied only to the quartz variety. However, since a similar-looking variety of oligoclase (feldspar) was also called aventurine, this name has become misleading. Therefore, the original mineral is also mentioned to distinguish it.

The name aventurine derives from the Italian "a ventura" meaning "by chance". This is an allusion to the lucky discovery of aventurine glass or goldstone at some point in the 18th century. One story is that this kind of glass was originally made accidentally at Murano by a workman, who let some copper filings fall into the molten "metal", whence the product was called avventurino. From the Murano glass the name passed to the mineral, which displayed a rather similar appearance. Although it was known first, goldstone is now a common imitation of aventurine and sunstone. Goldstone is distinguished visually from the latter two minerals by its coarse flecks of copper, dispersed within the glass in an unnaturally uniform manner. It is usually a golden brown, but may also be found in blue or green.

In Murano near Venice, at the beginning of the 18th century, a shimmering red-gold, opaque glass was created by chance (Italian: a ventura) and in a secret manner, after which the similar-looking quartz variety discovered later was named. The artificial product, although softer, was much more beautiful in appearance than the natural one and was preferred.

At the end of the 19th century, Friedrich Wöhler and Max von Pettenkofer developed a process for producing aventurine glass similar to the old Venetian glass. The shimmer in the iron-colored glass flux consists of metallic copper, dispersed in its crystal planes within the molten mass. The copper is added to the glass set as copper(I) oxide, where it is reduced to metal. The glass is processed into fake jewelry, shirt buttons, bracelets, etc.

By rolling mica flakes into the glass mass, masses are also created which are then blown or cast into objects that also bear the name aventurine glass.

Green aventurine glass was first produced in 1865 by the French chemist Pelouze and has since been processed in increasing quantities into costume jewelry in French factories.

Here, the glass is given an essential ingredient, chromium (in the form of potassium dichromate). During melting, chromium oxide is formed, which vitrifies and tints the glass green, a fact that has long been known. The special effect, however, is achieved by adding more chromium than can be vitrified; the excess then crystallizes into shiny, black-brown crystals, giving the material a very attractive appearance. Lacquerwork with a similar appearance is called aventurine lacquer; this is produced primarily in Japan.

Aventurine feldspar or sunstone can be confused with orange and red aventurine quartzite, although the former is generally of a higher transparency. Aventurine is often banded and an overabundance of fuchsite may render it opaque, in which case it may be mistaken for malachite at first glance.

The majority of green and blue-green aventurine originates in India (particularly in the vicinity of Mysore and Chennai) where it is employed by prolific artisans. Creamy white, gray and orange material is found in Chile, Spain and Russia. Most material is carved into beads and figurines with only the finer examples fashioned into cabochons, later being set into jewelry.

Properties

The most common color of aventurine is green, but it can also be orange, brown, yellow, blue, or grey. Chrome-bearing fuchsite (a variety of muscovite mica) is the classic inclusion and gives a silvery green or blue sheen. Oranges and browns are attributed to hematite or goethite. Because aventurine is a rock, its physical properties vary: its specific gravity may lie between 2.64–2.69 and its hardness is somewhat lower than single-crystal quartz at around 6.5.

Color varieties

Gold-red to brown-red aventurine quartz – mica or hematite flakes; often confused with aventurine feldspar (sunstone)

green aventurine quartz – enclosed fuchsite flakes

blue aventurine quartz – enclosed crocidolite or rutile fibers

Use as a gemstone

Aventurine quartz is used almost exclusively as a gemstone, preferably in pearl necklaces, solid bracelets, rings, earrings, or tumbled stones, as these round, cabochon -like shapes particularly emphasize the stone's shimmering luster. This material has also been used in the manufacture of smaller and larger art objects such as vases, tabletops, boxes, and other items.

In addition to aventurine feldspar, jade and nephrite are also visually similar to aventurine quartz and can be confused with it.

Esotericism

In esotericism, aventurine quartz is used as a healing stone. It is said to help with eczema, allergies, acne, and hair loss, as well as alleviate eye diseases. It is also said to promote mental flexibility and provide inner peace and serenity. There is no scientific evidence for this.

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