Calcite

Calcite is a carbonate, very common mineral and has a very special ability, double refraction.

The most special characteristic is double refraction when the sample is very clear.

Will take any unpolarized light and split it in two at two different angles.

Calcite can be used at cement, construction and protector layer for metals.

Calcite and aragonite are polymorphic, which means that both have the same chemical formula, like diamond and graphite.

But calcite forms trigonal crystals and aragonite orthorombic crystals.

When the samples are too small, it is hard to distinguish them and complex optical tests are necessary.

They get often wrong tags.

Calcite is chemicaly is similar with aragonite and vaterite.

Similar minerals: aragonite (polymorphic), dolomite

A isomorphous mineral is also Cerussite.

Chemical formula: CaCO3

Compozitie: 40,04% calcium; 12% carbon; 47,96% oxygen; 56,03% CaO; 43,97% Co2

Scrystal system: trigonal or tirclinic

Color: colorless, white, gray, yellow and even pink, red, green, brown or black

Can be transparent, translucent or opaque

Streak white

Hardness 3 Mohs

Cleavage perfect

habitus stalactitic

Density: 2,71

Special characteristics:

Double refraction with dispersion angle up to 25 degree

Can be thermoluminoscent, triboluminoscent, fluorescent and phosphorescent

Fluorescent and phosphorescent in short UV with yellow, blue, green, red and long UV yellow, blue, green, and red color

After exposed to ultraviolet and turning the light off, some calcite may keep glow in the dark, ability named phosphorescence

Tests:

Reacts chemicaly with hydrochloric acid and other acids

Some calcites becomes fluorescent when heated

Hardness of 3 Mohs and white streak

Double refraction if is clear crystal

Yellow calcite on the left and on right it's glow in the dark ability after exposed to ultraviolet for short time and let it in the dark

A sphere of Yellow Calcite

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