What is quartz??

What is Quartz??

Quartz is the second most abundant mineral in the earths crust, after feldspar.  Tere are many different varieties of quartz, several of which are semi-precious gemstones. 

Major varieties of quartz

Chalcedony - Cryptocrystalline quartz and moganite mixture. The term is generally only used for white or lightly colored material. Otherwise more specific names are used.

Agate - Multi-colored, banded chalcedony, semi-translucent to translucent

Onyx - Agate where the bands are straight, parallel and consistent in size.

Jasper - Opaque cryptocrystalline quartz, typically red to brown

Aventurine - Translucent chalcedony with small inclusions (usually mica) that shimmer.

Tiger's eye - Fibrous gold to red-brown colored quartz, exhibiting chatoyancy.

Rock crystal - Clear, colorless

Amethyst - Purple, transparent

Citrine - Yellow to reddish orange to brown, greenish yellow

Prasiolite - Mint green, transparent

Rose quartz Pink, translucent, may display diasterism

Rutilated quartz - Contains acicular (needle-like) inclusions of rutile

Milky quartz - White, translucent to opaque, may display diasterism

Smoky quartz - Brown to gray, opaque

Carnelian - Reddish orange chalcedony, translucent

Dumortierite quartz - Contains large amounts of dumortierite crystals

Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucent, and has often been used for hardstone carvings, such as the Lothair Crystal. Common colored varieties include citrine, rose quartz, amethyst, smoky quartz, milky quartz, and others.

The most important distinction between types of quartz is that of macrocrystalline and the microcrystalline or cryptocrystalline varieties . The cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline.

Chalcedony is a cryptocrystalline form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite.  Other opaque gemstone varieties of quartz, or mixed rocks including quartz are agate, carnelian or sard, onyx, heliotrope, and jasper.

Amethyst

Amethyst is a popular form of quartz that ranges from a bright to dark or dull purple color. The world's largest deposits of amethysts can be found in Brazil, Mexico, Uruguay, Russia, France, Namibia and Morocco. Sometimes amethyst and citrine are found growing in the same crystal. It is then referred to as ametrine. An amethyst is formed when there is iron in the area where it was formed.

Citrine

Citrine is a variety of quartz whose color ranges from a pale yellow to brown due to ferric impurities. Natural citrines are rare; most commercial citrines are heat-treated amethysts or smoky quartzes. However, a heat-treated amethyst will have small lines in the crystal, as opposed to a natural citrine's cloudy or smokey appearance. It is nearly impossible to tell cut citrine from yellow topaz visually, but they differ in hardness. Brazil is the leading producer of citrine, with much of its production coming from the state of Rio Grande do Sul. The name is derived from Latin citrina which means "yellow" and is also the origin of the word "citron". Sometimes citrine and amethyst can be found together in the same crystal, which is then referred to as ametrine. Citrine has been referred to as the "merchant's stone" or "money stone", due to a superstition that it would bring prosperity.

Rose quartz

Rose quartz is a type of quartz which exhibits a pale pink to rose red hue. The color is usually considered as due to trace amounts of titanium, iron, or manganese, in the massive material. Some rose quartz contains microscopic rutile needles which produces an asterism in transmitted light. Recent X-ray diffraction studies suggest that the color is due to thin microscopic fibers of possibly dumortierite within the massive quartz.

Additionally, there is a rare type of pink quartz (also frequently called crystalline rose quartz) with color that is thought to be caused by trace amounts of phosphate or aluminium. The color in crystals is apparently photosensitive and subject to fading. The first crystals were found in a pegmatite found near Rumford, Maine, USA and in Minas Gerais, Brazil.

Smokey quartz

Smokey quartz is a gray, translucent version of quartz. It ranges in clarity from almost complete transparency to a brownish-gray crystal that is almost opaque. Some can also be black.

Milky quartz

Milk quartz or milky quartz is the most common variety of crystalline quartz. The white color is caused by minute fluid inclusions of gas, liquid, or both, trapped during crystal formation making it of little value for optical and quality gemstone applications.

Artificial Quartz

Some varieties of quartz are not naturally occurring. For example, some clear quartz crystals can be treated using heat or gamma-irradiation to induce color where it would not otherwise have occurred naturally. Susceptibility to such treatments depends on the location from which the quartz was mined.

Prasiolite, an olive colored material, is produced by heat treatment; natural prasiolite has also been observed in Lower Silesia in Poland. Although citrine occurs naturally, the majority is the result of heat-treated amethyst (article about citrine coming).Another popular stone, Carnelian, is widely heat-treated to deepen its color.

Because natural quartz is often twinned, synthetic quartz is produced for use in industrial purposes. Large, flawless, single crystals are synthesized in an autoclave (sort of like a big pressure cooker) via the hydro thermal process; This is the same method used to create synthetic emerals.

Like other crystals, quartz may be coated with metal vapors to give it an attractive sheen. (Aura Quartz)