Since the transformation is accompanied by a significant change in volume, it can easily induce microfracturing of ceramics or rocks passing through this temperature threshold.

Since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry and hardstone carvings, especially in Europe and Asia.

[13] Some sources, however, attribute the word's origin to the Saxon word Querkluftertz, meaning cross-vein ore.[14][15] The Ancient Greeks referred to quartz as κρύσταλλος (krustallos) derived from the Ancient Greek κρύος (kruos) meaning "icy cold", because some philosophers (including Theophrastus) understood the mineral to be a form of supercooled ice.

[16] Today, the term rock crystal is sometimes used as an alternative name for transparent coarsely crystalline quartz.

[17][18] Roman naturalist Pliny the Elder believed quartz to be water ice, permanently frozen after great lengths of time.

Both α-quartz and β-quartz are examples of chiral crystal structures composed of achiral building blocks (SiO4 tetrahedra in the present case).

The transformation between α- and β-quartz only involves a comparatively minor rotation of the tetrahedra with respect to one another, without a change in the way they are linked.

[22][27] However, there is a significant change in volume during this transition,[28] and this can result in significant microfracturing in ceramics during firing,[29] in ornamental stone after a fire[30] and in rocks of the Earth's crust exposed to high temperatures,[31] thereby damaging materials containing quartz and degrading their physical and mechanical properties.

Chalcedony is a cryptocrystalline form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite.

Amethyst is a form of quartz that ranges from a bright vivid violet to a dark or dull lavender shade.

The world's largest deposits of amethysts can be found in Brazil, Mexico, Uruguay, Russia, France, Namibia, and Morocco.

[38] Ametrine, as its name suggests, is commonly believed to be a combination of citrine and amethyst in the same crystal; however, this may not be technically correct.

[42] Inclusions of the mineral dumortierite within quartz pieces often result in silky-appearing splotches with a blue hue.

[46] Unlike natural citrine, the color of heat-treated amethyst comes from trace amounts of the iron oxide minerals hematite and goethite.

Brazil is the leading producer of citrine, with much of its production coming from the state of Rio Grande do Sul.

The white color is caused by minute fluid inclusions of gas, liquid, or both, trapped during crystal formation,[50] making it of little value for optical and quality gemstone applications.

Recent X-ray diffraction studies suggest that the color is due to thin microscopic fibers of possibly dumortierite within the quartz.

Since 1950[citation needed], almost all natural prasiolite has come from a small Brazilian mine, but it is also seen in Lower Silesia in Poland.

[58] Quartz crystals have piezoelectric properties; they develop an electric potential upon the application of mechanical stress.

More frequently, bulldozers and backhoes are used to remove soil and clay and expose quartz veins, which are then worked using hand tools.

Coesite is a denser polymorph of SiO2 found in some meteorite impact sites and in metamorphic rocks formed at pressures greater than those typical of the Earth's crust.

Cutting, grinding, chipping, sanding, drilling, and polishing natural and manufactured stone products can release hazardous levels of very small, crystalline silica dust particles into the air that workers breathe.

[70] Crystalline silica of respirable size is a recognized human carcinogen and may lead to other diseases of the lungs such as silicosis and pulmonary fibrosis.

[79][80] Quartz is the most common material identified as the mystical substance maban in Australian Aboriginal mythology.

It is found regularly in passage tomb cemeteries in Europe in a burial context, such as Newgrange or Carrowmore in Ireland.

[81] 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.

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.

In the United States, the U.S. Army Signal Corps contracted with Bell Laboratories and with the Brush Development Company of Cleveland, Ohio to synthesize crystals following Nacken's lead.

[88][89] (Prior to World War II, Brush Development produced piezoelectric crystals for record players.)