The second most abundant mineral on Earth (12% by volume), Quartz, has been found on every continent. The word "quartz" is derived from the German word "quartz". Other sources attribute the word's origin to the Saxon word Querkluftertz, meaning cross-vein ore. The Irish word for quartz is grian cloch, which means 'stone of the sun'.

 

Quartz goes by an array of different names. The most important distinction between types of quartz is that of macrocrystalline (individual crystals visible to the unaided eye) and the microcrystalline or cryptocrystalline varieties (aggregates of crystals visible only under high magnification). The cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline. Common single crystal varieties include rock crystal, smokey quartz, blue quartz, citrine, amethyst, rose quartz, and others. Masses of microscopic crystals are considered cryptocrystalline. These include tiger's eye, agate, onyx , and carnelian.

 

Rose quartz is not popular as a gem – it is generally too clouded by impurities to be suitable for that purpose. Rose quartz is more often carved into figures such as people or hearts. Smoky 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.

 

Quartz is an essential constituent of granite and other felsic igneous rocks. It is very common in sedimentary rocks such as sandstone and shale and is also present in variable amounts as an accessory mineral in most carbonate rocks. Because of its resistance to weathering it is very common in stream sediments and in residual soils.

 

Well-formed crystals may reach several meters in length and weigh hundreds of kilograms. Naturally occurring quartz crystals of extremely high purity, necessary for the crucibles and other equipment used for growing silicon wafers in the semiconductor industry, are expensive and rare. A major mining location for high purity quartz is the Spruce Pine Gem Mine in Spruce Pine, North Carolina.

 

While jade has been since earliest times the most prized semi-precious stone for carving in East Asia and Pre-Columbian America, in Europe and the Middle East the different varieties of quartz were the most commonly used for the various types of jewelry and hardstone carving, including engraved gems and cameo gems, rock crystal vases, and extravagant vessels. The tradition continued to produce objects that were very highly valued until the mid-19th century, when it largely fell from fashion except in jewelry. Cameo technique exploits the bands of color in onyx and other varieties.