Calcite

Calcite is really a mineral that is typical the world but faceted gems are rare since it is one of the most difficult gems to cut. The Calcite can be easily burned off by soaking it in acid. This is because of its low hardness (3.0), perfect cleavage in three directions and sensitivity to temperature. Calcite is just a calcium carbonate mineral, however the only one. There are three minerals, or phases, of CaCO3. Aragonite and Vaterite are polymorphs (Latin for “many shapes”) with Calcite, meaning they all have the chemistry that is same but different crystal structures and symmetries. Aragonite is orthorhombic, Vaterite is hexagonal and Calcite is trigonal.

Calcite is just a treasure that is beautiful is doubly refractive and available in many colors. Calcite is very extremely reactive to even the weakest of acids such as for example vinegar. Other important properties of Calcite are its fluorescence, phosphorescence, triboluminescence, and thermoluminescence. Not all Calcite specimens demonstrate these properties many do very well. Notable examples are specimens from Franklin, NJ-new jersey, USA where massive kinds of Calcite contain a small amount of manganese that causes it to fluoresce brightly under UV light that is red. Some Calcite specimens from Mexico can fluoresce purple that is beautiful blue colors and some unusual specimens will phosphoresce (continue to glow) even after the UV source is removed. Triboluminescence is another one of Calcite’s properties however it is very hard to demonstrate. It should happen when a Calcite specimen glows (in the dark) after being put or struck under pressure.

Mexican Onyx is really a variety of Calcite but not the same as Onyx that is really a variety of Quartz. Mexican Onyx can be used for carvings and decorative decorations such as vases, bookends, and animal that is tiny. Iceland Spar is another variety of Calcite that is well referred to as rhombohedral that is colorless pieces often available in rock shops. When these pieces are placed in a newspaper or other printed material it creates two slightly offset images. This is because of Calcite’s extreme double refraction, or splitting of light into two beams traveling at different speeds.

 

Category:	Carbonate minerals
Chemical Formula:	CA(CO3)
	Calcium Carbonate
Molecular Weight:	100.09 gm

Composition:	Calcium	40.04 %	Ca	56.03 %	CaO
	Carbon	12.00 %	C	43.97 %	CO2
	Oxygen	47.96 %	O
		100.00 %		100.00 %	= TOTAL OXIDE

 

Crystallography:	Trigonal – Hexagonal Scalenohedral
Crystal Habit:	Well-formed crystals are common, thin to thick tabular, with combinations of over 1000 forms noted, to 7 m; granular, stalactitic, in concretions, massive. Over 800 different forms have been described. Most commonly as acute rhombohedrons or prismatic with scalenohedral terminations, or combinations of the two.
Twinning:	At least four twin laws have been described, the most common being when the twin plane and the composition plane are {0112}. Also common with twinning on {0001} with {0001} as the compositional surface, producing re-entrant angles. Uncommon with {1011} or {0221} as twin planes, producing somewhat heart-shaped crystals (“butterfly” twins).

 

Cleavage:	Perfect on {1011}
Fracture:	Irregular/Uneven, Step-like
Tenacity:	Brittle
Moh’s Hardness:	3.0
Density:	2.7102 (g/cm3)
Luminescence:	Maybe fluorescent under LW UV, mid-range UV or SW UV as well as under X-rays, cathode rays, and even sunlight, in a number of colors and shades, commonly an intense red under SW UV with Mn as an activator (such as at Franklin, New Jersey, USA). Rarely Triboluminescent.
Radioactivity:	Not Radioactive

 

Color:	Colorless or White, also Gray, Yellow, Green, many other colors from included minerals; Colorless in transmitted light.
Transparency:	Transparent, Translucent to Opaque
Luster:	Vitreous to Pearly (on cleavages). Can be dull or earthy in chalk variety.
Refractive Index:	1.486 – 1.660  Uniaxial ( – ); anomalously Biaxial
Birefringence:	0.154 – 0.174 (high)
Dispersion:	Very Strong
Pleochroism:	None