COMPOSITION
Calcium Carbonate ( 56% CaO, 44%
CO2; Mn, Fe, and Mg may partially replace the Ca).
DISTINGUISHING
CHARACTERISTICS
Fluorescence, phosphorescence, thermoluminescence and
triboluminescence are other important properties of calcite. Calcite is
frequently fluorescent, a small amount of manganese is enough to make it
glow red under some wave lengths of ultraviolet light. Such as those
from Franklin, New Jersey. Some Mexican Iceland spar can fluoresce a
nice purple or blue color and unique specimens will even phosphoresce
(continue to glow) after the UV source has been removed.
Triboluminescence should occur in most specimens, but is not easily
demonstrated. In a dark room strike the specimen and it should glow.
Calcite is not the only calcium carbonate mineral. There are no less
than three minerals or phases of CaCO3. Aragonite and vaterite are polymorphs
with calcite, meaning they all have the same chemistry, but different
crystal structures and symmetries. Aragonite is orthorhombic, vaterite
is hexagonal and calcite is trigonal. Aragonite is a common mineral,
Vaterite on the other hand is extremely scarce and rarely seen.
Aragonite will over time convert to calcite and calcite pseudomorphs
after aragonite are not uncommon.
ENVIRONMENT
Calcite forms in all types of occurrences, with all
classes of rock. Calcite is the primary mineral component of limestone
and its metamorphic form is marble. It forms oolitic, fossiliferous and
massive limestones in sedimentary environments and even serves as the
cements for many sandstone's and shale's. Most calcite is white, though
various impurities may tint it almost any color, even black. Calcite is commonly a late vein mineral
and may need to be removed with a very dilute hydrochloric acid solution
to reveal well-formed crystals of other minerals.
CRYSTAL DESCRIPTION
It is noted for its
beautiful varieties and its perfect crystals. Also its the stable form
of the widely distributed mineral calcium carbonate (CaCO3).Crystal Habits are extremely variable
with almost any trigonal or pseudo-hexagonal form possible. One of it's
most well known crystal forms is the scalenohedron or "Dogtooth" Other
common crystal forms are rhombohedron, hexagonal prism and pinacoid.
There are more than 300 crystal forms identified in calcite and these
forms can combine to produce literally a thousand different crystal
variations. Calcite also produces many twin varieties that are favorites
among twin collectors. There are also phantoms, included crystals, color
varieties, pseudomorphs and unique associations. Calcite is
polymorphous, (having the same chemical formula but different crystal
structure) with the minerals aragonite and vaterite as well as with
several other forms that apparently exist only under extreme
experimental conditions. Calcite comes in many other forms too. Such as
massive, fibrous, concretionary, stalactitic, nodular, oolitic,
stellate, dendritic, granular and so on.
TESTS
Easily scratched, dissolves in cold
dilute hydrochloric acid or vinegar
with effervescence. Other carbonates such as dolomite or siderite do not
react as easily with these acids as does calcite and this leads to
differentiating these somewhat similar minerals more readily. Aragonite
dissolves as easily, but has a different crystal form and no cleavage.
When heated, aragonite crumbles to powder and loses its fluorescence.
Even when not previously fluorescent, calcite usually becomes soft
after heating
LOCALITIES
Older more famous localities are Palm
Wash, California; Missouri- Kansas-Oklahoma ( tri state lead district);
Iceland (the original Iceland spar). Oolitic calcite sand forms on the
shores of Great Salt Lake. Also the Pugh Quarry, Ohio; Rosiclare,
Illinois; Franklin, New Jersey; Elmwood, Tennessee; Germany; Brazil;
Guanajuato, Mexico; Cornwall, Durham and Lancashire, England; Bombay
area of India and many Brazilian and Tanzania.
BLUE CALCITE IN
TANZANIA
Blue calcite in Tanzania is
found in Babati District within the Arusha Region plus different areas
within the Arusha region.Its availability its very huge volumes.Plus
also its found in other regions but we cant disclose those areas
at public domain.
USES
Calcite is also used in chemical and optical uses and as
mineral specimens. Flawless transparent calcite is used in optical
instruments especially in geological (polarizing)
microscopes.
FACTS & HISTORY
Calcite name originates from Greek
Name "Chalix", the greed word for Lime.
It comprises about 4% by
weight of the Earth's crust and is formed in many different geological
environments.
Calcite is the primary mineral component in cave
formations. Stalactites and stalagmites, cave veils, cave pearls, "soda
straws" and the many other different cave formations are made of
calcite.
Another well known variety is "Iceland Spar", which is
basically clear cleaved fragments of completely colorless (ice-like)
calcite. Originally discovered and named after Eskifjord, Iceland, where
the calcite is found in basalt cavities.
Iceland spar is used for
optical equipment and during World War II it was a strategic mineral.
Iceland spar also best demonstrates the unique property of calcite,
called double refraction. Double refraction occurs when light enters the
crystal and calcite's unique optical properties, split the light into
fast and slow beams. As these two beams exit the crystal they are bent
into two different angles. This is the term known as angle of
refraction. Because the angle is
