A cleavage fragment of calcite showing its typical rhombohedral cleavage.
Note the incipient cleavage planes. This photo shows the optical phenomena
known as DOUBLE REFRACTION that is so nicely displayed in this clear calcite
fragment - note how the grid pattern is double when viewed through the calcite.
"Dog
tooth" calcite is a common form of calcite and represents the scalenohedral
crystal development. This specimen shows associated dolomite and is from
Lockport, New York.
A complex
growth of rhombohedral calcite from Mount Vernon, Indiana.
Prismatic crystals of Calcite are often called "nail head" spar.
Rhombohedral pinkish crystals of Calcite with minor amounts of Quartz from Peru.
Various
colors of calcite.
This
is a stack of tabular calcite crystals called "poker chip" calcite.
Calcite with Hematite inclusions
MMT309 from Chihuahua, Mexico; Mine: Santa Eulalia
Calcite with minor amounts of
Hematite from Mexico
CHEMISTRY CaCO3 Calcium Carbonate
CRYSTALLOGRAPHY Hexagonal, rhombohedral
CRYSTAL GROWTH AND HABITS Over 300 forms have been described but there are 3 main habits: prismatic, rhombohedral and scalenohedral. Calcite also occurs as fine to coarse granular aggregates, encrustations and stalactitic growths.
COLOR AND OTHER OPTICAL PROPERTIES It is clear when pure, but Calcite can take on a tremendous variety of colors by virtue of inclusion of minor impurities. Colors include: red, orange, yellow, green, blue brown and black. Calcite can be transparent, translucent or opaque. It shows strong double refraction.
HARDNESS 3
SPECIFIC GRAVITY 2.72
LUSTER Vitreous to earthy
STREAK White
BREAKABILITY Calcite has perfect rhombohedral cleavage (3 directions) with angles of 74.9o.
OCCURRENCE Calcite is one of the most common and widely distributed minerals on the planet. It is found in all rock types as well as vein filling materials and as caliche in arid environments.
OTHER Reacts (bubbles) readily in cold, dilute hydrochloric acid (HCl).