How do you recognize quartz

Differentiate between calcite and quartz

What is calcite What is quartz Carbonate versus oxide mineral.

Similarities between calcite and quartz

colour: It is difficult to distinguish between calcite and quartz on the basis of color alone. Both minerals are transparent in their pure form. The different colors of calcite and quartz result from impurities, admixtures of other elements, inclusions of gases or liquids, but also defects in the structure of the crystal lattice. Like quartz, calcite can also be white, orange, yellow, red, green, violet-blue, brown or gray.

Compared to calcite, the colored variants of quartz are known under their own names: rock crystal (colorless), citrine (yellow, orange), milk quartz (white), agate (green, orange, brown, red), smoky quartz (brown, gray), pink (Rose quartz) and purple (amethyst).

Picture 1: quartz; From left to right: rock crystal, smoky quartz, rose quartz and amethyst

Line color: If you rub calcite and quartz over an unglazed porcelain board, a so-called streak board, a white line appears in both cases, the color of the line.

Image 2: Calcite: from left to right: orange calcite, spherical calcite, sintered calcite and cobalt calcite

Gloss and transparency: The gloss of quartz and calcite is similar to that of glass. There is also similarity in terms of transparency: both minerals have a transparent to translucent transparency; i.e. you can see through the crystals of calcite as well as quartz with all its varieties or you can see light shining through if you hold these minerals against the sunlight.

fracture: When calcite and quartz break, they both show the same pattern. The fracture point shows circular grooves - called a shell-like fracture.

Differences between calcite and quartz

composition: The name calcite already gives a first indication of the composition of the mineral. Calcite is translated as calcareous stone, the chemical composition of which has the formula CaCO3 is described. In contrast, quartz is an oxide mineral consisting of SiO2.

hardness: With a Mohs hardness of 6.5 to 7, quartz is more than twice as hard as calcite. Calcite, whose hardness is 3 on the Mohs scale, could still be scratched with a knife. Quartz and all its varieties are not.

Image 3: Crystals in comparison: rhombohedral Iceland spar (calcite) and rock crystal

Crystals: At first glance, the crystals of calcite and quartz are very similar, but on closer inspection, the differences become clear. Quartz crystals have six sides, usually with a pyramid-shaped crystal tip. But there are also quartzes that deviate from this ideal shape and are rather bulky.
The crystals of calcite, on the other hand, can be rhombohedral (= crystal with six diamond-shaped faces, particularly memorable as an example par excellence based on Iceland spar) or scalenohedral (= crystal composed of triangles with unequal lengths with different numbers of faces), which makes calcite one of the richest in shapes Mineral in the world of minerals. The aggregates differ accordingly: Quartz is massive and granular - just like calcite, which can also be oolithic (spherical), stalactic or powdery.

Behavior in acid: Quartz is not soluble in any acid except hydrofluoric acid. Cold, dilute hydrochloric acid cannot dissolve quartz, but calcite can, which foams at the same time.

See also:
⇒ Differentiate between lapis lazuli and sodalite
⇒ Differentiate between almandine (garnet) and magnetite
⇒ Differentiate between granite and gneiss

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⇒ Bauer, J .; Tvrz, F. (1993): The Cosmos Mineral Guide. Minerals rocks precious stones. An identification book with 576 color photos. Gondrom Verlag GmbH Bindlach
⇒ Korbel, P .; Novak, M. and W. Horwath (2002): Mineralien Enzyklopädie, Dörfler Verlag
⇒ Medenbach, O .; Sussieck-Fornefeld, C .; Steinbach, G. (1996): Steinbach's natural guide minerals. 223 species descriptions, 362 color photos, 250 drawings and 30 pages of identification tables. Mosaik Verlag Munich
⇒ Schumann, W. (1992): Precious and precious stones: all precious and precious stones in the world; 1500 unique pieces. BLV determination book, BLV Verlagsgesellschaft mbH Munich
⇒ Schumann, W. (1991): Minerals rocks - characteristics, occurrence and use. FSVO nature guide. BLV Verlagsgesellschaft mbH Munich

Last updated: March 2, 2021

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