Mineralpedia Details for Calcite

Named for an important industrial use of the mineral after the Latin word calx, or calce, for “lime.” Calcite is extremely common and widespread, and it is an important rock forming mineral and is common in limestone, marble, chalk, as a cement, hydrothermal veins, igneous rocks, and caves. Calcite is highly variable in color and forms, but it is most easily recognized by its reactivity to hydrochloric acid and even weaker acids like vinegar, which it will effervesce strongly when in contact with. Calcite can fluoresce red, blue, yellow, and many other colors and shades under both long-wave and short-wave ultraviolet light. It is also phosphorescent, cathodoluminescent, thermoluminescent and occasionally triboluminescent. Another telling property of Calcite is its strong optical birefringence which causes a double refraction, and thus double image, which can be viewed by looking at objects through a clear calcite specimen.

Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/calcite.pdf

Formula

CaCO₃ 

Crystal System

Trigonal 

Crystal Habit

Crystalline - Coarse, Stalactitic, Massive 

Cleavage

Perfect, Perfect, Perfect 

Luster

Vitreous (Glassy) 

Color

colorless, white, pink, yellow, brown 

Streak

white 

Class

Trigonal - Hexagonal Scalenohedral 

Fracture

Brittle - Conchoidal 

Hardness

3 

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Soft yellowish brown colored Calcite with crystals from 4 to 5 cm, one is doubly terminated. 

Large 4cm Calcite crystals showing striated faces with included Orpiment and external, prismatic, bright red Realgar crystals to 7mm. 

Glassy purplish pink Calcite rhombs to 5mm.

Clear Calcite crystal on Dolomite. 1cm.

An aestethic group of huge nearly 5cm translucent white Calcite crystals that are very well formed and take an interesting nailhead/modified rhombohedral form. Classic and highly sought locality for the Wisconsin collectors! Minor scuffing. Minor fluorescence to a light orange.

You've seen plenty of these on the market these days. It's a popular American locality which has produced countless beautiful groups of Fluorite, Calcite, Sphalerite and Barite. This specimen is nearly flawless, albeit, a partially cleaved matrix base, although you can expect that with any Elmwood piece. This crystal has the best amber orange color sought after in these pieces, the luster is great and the crystal edges are sharp. The large main crystal is 9cm long, You can see the twin plane in a few photos. With a little help, it displays marvelously.

Aesthetic specimen of orange, discoidal Calcite to over 1cm in nice clusters on Quartz. The original tag (prov. tab) shows it to be from the "Coronation Lode" of the Geevor mine.