Crystal Celestite

Chemical Formula

CaCO₃

Composition

Calcium carbonate, sometimes with impurities of iron, magnesium, or manganese, and occasionally zinc and cobalt.

Variable Formula

(Ca,Fe,Mg,Mn,Zn,Co)CO₃

Color

Colorless, white, yellow, brown, orange, pink, red, purple, blue, green, gray, black. May also be multicolored or banded.

Streak

White

Hardness

3

Crystal System

Hexagonal

Crystal Forms 
and Aggregates

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.

Transparency

Transparent to opaque

Specific Gravity

2.7

Luster

Vitreous

Cleavage

1,3 - rhombohedral

Fracture

Conchoidal. Rarely observed due to the perfect cleavage.

Tenacity

Brittle

Other ID Marks

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.

Complex Tests

1) Effervescent in hydrochloric acid and most other acids.
2) Calcite that doesn't fluoresce usually becomes fluorescent upon heating.

In Group

Carbonates; Calcite Group

Striking Features

Hardness, cleavage, fluorescence, and effervescence with hydrochloric acid.

Environment

Calcite is a constituent of all mineral environment, including sedimentary, igneous, and metamorphic.

Rock Type

Igneous, Sedimentary, Metamorphic

Popularity (1-4)

1

Prevalence (1-3)

1

Demand (1-3)

1