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Chemical Formula
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CaCO3
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Composition
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Calcium carbonate, sometimes with impurities of iron, magnesium, or manganese, and occasionally zinc and cobalt.
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Variable Formula
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(Ca,Fe,Mg,Mn,Zn,Co)CO3
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Color
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Colorless, white, yellow, brown, orange, pink, red, purple, blue, green, gray, black. May also be multicolored or banded.
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Streak
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White
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Hardness
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3
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Crystal System
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Hexagonal
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Crystal Forms
and Aggregates
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Occurs in a great variety of shapes, with the most common forms asrhombohedral and scalenohedralcrystals. Crystals may be tabular, acicular, prismatic, flaky, and needle-like. May occur as bundles ofscalenohedrons, intergrown rhombohedrons, hair-like masses of acicular crystals, grainy, stalactitic,fibrous, massive, and earthy. Scalenohedral twinning is common.
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Transparency
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Transparent to opaque
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Specific Gravity
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2.7
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Luster
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Vitreous
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Cleavage
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1,3 - rhombohedral
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Fracture
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Conchoidal. Rarely observed due to the perfect cleavage.
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Tenacity
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Brittle
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Other ID Marks
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1) Commonly fluorescent; specimens from different localities fluoresce different colors. Some Calcite is also phosphorescent.
2) Transparent crystals exhibit strong double refraction.
3) May be thermoluminescent.
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Complex Tests
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1) Effervescent in hydrochloric acid and most other acids.
2) Calcite that doesn't fluoresce usually becomes fluorescent upon heating.
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In Group
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Carbonates; Calcite Group
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Striking Features
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Hardness, cleavage, fluorescence, and effervescence with hydrochloric acid.
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Environment
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Calcite is a constituent of all mineral environment, including sedimentary, igneous, and metamorphic.
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Rock Type
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Igneous, Sedimentary, Metamorphic
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Popularity (1-4)
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1
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Prevalence (1-3)
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1
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Demand (1-3)
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1
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