Quartz

What quartz is: silicon dioxide, and what the IMA list records

Quartz is SiO2, and the Handbook’s Chemistry field reads simply SiO2 with traces of other elements. Worked on standard atomic weights, the formula mass is 60.08, and silicon is 46.74% of it by mass, oxygen 53.26%. The September 2026 IMA-CNMNC Master List gives quartz the status A, 1967 s.p., and the country unknown. The name, says the sheet, is of obscure origin in the Middle Ages, first applied to gangue in Saxony, Germany.

Polymorphs. The sheet lists cristobalite, tridymite, coesite and stishovite as polymorphs, the same composition in other structures, and closes the line stable below 573 °C. It records quartz as piezoelectric and pyroelectric, and as possibly triboluminescent.

Its company. The Association field reads calcite, fluorite, feldspars, epidote, chlorite, micas, zeolites, many other species, and the Distribution field opens Extraordinarily common. Its settings run from hydrothermal veins, granites and granite pegmatites to sandstones, quartzites and soils. The difference between the mineral and a crystal of it is on crystal vs mineral.

Amethyst, citrine, smoky and rose quartz: colour names for one species

The variety names are colour names. The USGS gemstone list gives quartz hardness 7 and specific gravity 2.65. It names its coarsely crystalline varieties: rock crystal, colourless; amethyst, purple; citrine, yellow to amber; morion, black; smoky quartz or cairngorm, smoky grey to brown; rose quartz, translucent pink; green quartz or praziolite, green. Chalcedony and jasper it lists separately, as cryptocrystalline varieties of silica. The Handbook sheet uses chalcedony for the fine-grained to microcrystalline habit.

Method: we searched the IMA list for amethyst, citrine, morion, cairngorm, prasiolite, praziolite, chalcedony, jasper, agate and rock crystal as row names. None is a row. On a label they are additions to quartz, not replacements for it.

What the sheet says about colour: colorless, white; from chemical or particulate inclusions, rose-pink to rose-red, yellow to yellowish brown, green, blue, bluish violet, brown to black; zoned or mottled. This page gives no other colour cause. Amethyst’s own questions are on how to tell if amethyst is real and why is my amethyst losing color. Blue minerals mistaken for it are on is celestite a quartz and is tourmaline a quartz.

How to tell quartz from calcite, fluorite and other clear minerals

The rule: hardness 7 and no good cleavage together point to quartz among the nine sheets in the table. Method: we extracted the Hardness and Cleavage fields of those nine Handbook sheets by script and searched each Cleavage field for perfect, distinct or good. Eight match; quartz, rarely observable, poor, does not. Quartz is also the only one of the nine whose hardness reaches 7. The rule covers only these nine, not every colourless mineral.

Why the order matters. Hardness is decisive against all eight: the next hardest in the table is hemimorphite at 4.5 to 5. A broken edge confirms it, because the other eight give flat cleavage faces where quartz gives a conchoidal, glassy break. The methods are on how to test mineral hardness properly and cleavage or fracture: how to tell. Calcite has its own page, how to tell calcite from quartz.

The scale helps against the heavy ones. A 20.00 g quartz piece weighs 12.45 g in water. Baryte gives 15.56 g and celestine 14.96 g. Fluorite gives 13.70 to 13.72 g. Calcite, at 12.62 g, is only 0.17 g away, and massive quartz narrows that further.

Quartz crystals: forms, handedness and the Dauphine, Brazil and Japan twins

The habit on the sheet: prisms {10-10} terminated by {10-11} and {01-11}, striated perpendicular to [0001], with over 500 forms noted. Crystals may be pseudocubic or dipyramidal, tapering, needlelike, flattened or distorted, rarely twisted. Quartz also occurs as drusy, fine-grained to microcrystalline and massive material. Horizontal striations across the prism faces are therefore part of the description, and a crystal terminated at both ends is covered on what is a double terminated crystal.

Twinning, as the sheet gives it: very common penetration twins on the Dauphiné law, about [0001], and on the Brazil law, with {11-20} as contact plane; contact twins on the Japan law, with {11-22} as contact plane, may be repeated; and several other laws. All three four-index forms satisfy h + k + i = 0, checked against the rendered sheet. Twin laws in general are on mineral twinning explained.

Worked size. The sheet’s largest figure is to 6 m and 36 t. At 2.65 g per cm³, 36 tonnes is 13.58 m³, a cube 2.39 m on a side. The sheet gives no locality for that crystal, and we add none.

Where fine quartz comes from, including Minas Gerais

The Distribution field names fine specimens from many places in the Alps of Switzerland and Austria; Carrara, Italy; Bourg d’Oisans, France; Mursinka and the Dodo mine in the Urals; Sakangyi, Myanmar; large twins from Yamanashi Prefecture, Japan; and Madagascar. In Brazil it gives large amounts from Rio Grande do Sul, Minas Gerais, Goiás and Bahia. It also names Artigas, Uruguay; Thunder Bay, Ontario; and Veracruz and Guerrero, Mexico.

In the USA the sheet lists Mt. Ida to Hot Springs, Arkansas; Middleville, Herkimer Co., New York; Alexander and Lincoln Cos., North Carolina; the Pala and Mesa Grande districts, California; the El Capitan Mountains, New Mexico; Crystal Park and Little Pipestone Creek, Montana; and the Pikes Peak area, Colorado. It names no British locality, and we add none.

Pegmatite quartz sits with the minerals on the tourmaline page; the quartz sheet itself lists fluorite, calcite, feldspars and micas among its associates. The rest of the section is at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.

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