Calcite is common and abundant throughout the world. The material has little intrinsic value since it is not scarce. However, calcite is one of the most difficult of all minerals to be cut because of perfect cleavage in 3 directions. The cost of faceted stone is therefore mostly in the labor of cutting. Normally, a faceted stone breaks during cutting, and the finished gem is much smaller than the originally intended size. Therefore, a cut calcite over 50 carats is extremely rare. Faceted stones cut from material from many localities might turn up, but the lack of scarcity value is not encouraging to potential calcite cutters.
Rough material can be very large (hundreds of carats). Colorless material is usually step-cut or emerald-cut. Brown material from Baja is usually seen up to 50 carats, normal range 5-25 carats. Purplish red material from Paramca, Spain (cobaltian) is not transparent, usually cut 1-5 carat size. Limestone onyx is opaque and yields cabochons and carvings of any desired size.
Common and from many localities around the world. SW: red, orange, lemon yellow, shades of green, shades of blue, pink, white. LW: orange, dull pink, tan, yellow, blue gray.
Dimorph of ARAGONITE. Also Cobaltocalcite = Sphaerocobaltite = CoCO3; Limestone onyx= Travertine = Flowstone (found in caves); Iceland spar; Alabaster; Marble.
OPTICS: e = 1.486-1.550; o = 1.658-1.740
Uniaxial (-)
OCCURRENCE: Occurs in all types of rocks as the most abundant carbonate mineral on Earth. Found in veins, ore deposits, and as a constituent of rock limestone and marble. Crystals often large (many inches) and transparent. Limestone onyx is the material of most limestone caves, usually banded in shades of tan and brown. (Note: this is not the quartz-variety onyx). Iceland spar is colorless calcite, transparent, sometimes in large masses. The name alabaster refers to gypsum and is incorrect when applied to calcite. Gem material is commonly seen from the following localities: Missouri (colorless), Baja California (brown), Canada, New York, Montana, England, Mexico, Iceland (colorless), and the USSR (pale yellow).
Royal Ontario Museum (Toronto, Ontario, Canada): 183 (colorless, Balmat, New York)
Gemological Institute of America: 48 (yellow, USSR)
COMMENTS: Calcite is common and abundant throughout the world. The material has little intrinsic value since it is not scarce. However, calcite is one of the most difficult of all minerals to be cut because of perfect cleavage in 3 directions. The cost of faceted stone is therefore mostly in the labor of cutting. Normally, a faceted stone breaks during cutting, and the finished gem is much smaller than the originally intended size. Therefore, a cut calcite over 50 carats is extremely rare. Faceted stones cut from material from many localities might turn up, but the lack of scarcity value is not encouraging to potential calcite cutters.
Limestone onyx is usually cut into slabs, made into vases, lamps, ashtrays, bookends, and many other decorative objects. It is usually banded in shades of brown, green, and buff. Marble is a metamorphic rock often used in construction and in making decorative carved objects. Coloration in the form of banding and streaks is due to impurities.
NAME: Calcite is derived from the Latin calx, meaning lime.
Some gems have an appeal beyond their appearance. If you’re looking for a gem with a story to tell, try these unique gem materials for jewelry design.…
IGS Newsletter
Subscribe to the Free IGS Newsletter!
IGS Become Member
Join IGS today for great benefits!
Exclusive access to our premium articles and courses
IGS Newsletter