Orange Calcite

Calcite occurs in most geological settings and is most common as massive material in limestone and marble; it also forms in hydrothermal deposits. A dealer in Pakistan reported that large quantities of orangy-yellow (and green) calcite were being mined in Baluchistan province. Laboratory records also list orangy-yellow calcite from Rosarito Beach, Baja California, Mexico, yellowish-orange calcite from the Czech Republic and brownish-orange calcite from Erongo, Namibia.

Like all calcite, it has a Mohs hardness of 3, three directions of perfect rhombohedral cleavage and very strong birefringence (about 0.172), and it fizzes readily in acids, even weak ones such as vinegar. An orangy-yellow calcite cabochon from Pakistan at first resembled opal or chalcedony; testing gave a spot refractive index of about 1.56 with the strong birefringence blink typical of carbonates, a specific gravity of 2.72 and yellow fluorescence under long- and short-wave UV, and it showed wide bands with fine fibrous inclusions. It can resemble yellow to orange aragonite, a polymorph with the same formula; the Japanese retailer Pascle says the two cannot be told apart by eye. Aragonite is orthorhombic, denser (specific gravity about 2.95 against about 2.71) and has one distinct cleavage instead of three perfect rhombohedral ones. Calcite may be dyed, impregnated with wax or plastic, or irradiated, so a strong colour in inexpensive beads is not by itself proof of natural colour.

Calcite (Mohs 3) scratches easily and splits readily along its cleavage. A care table based on GIA's Gem Reference Guide advises never using ultrasonic or steam cleaners; warm soapy water is usually safe. Keep it away from acids, which make it effervesce, and from high heat, at which it can crack apart (decrepitate). The same table lists natural calcite colours as stable to light.

The mineral name calcite comes from the Latin calx, "lime". Mindat describes it as an ancient name and credits Pliny the Elder (AD 79) with naming it as a mineral. Colour names such as this one are descriptive trade names, not separate mineral names.

The Japanese retailer Pascle writes that stones of the calcite group are said to settle unstable emotions and smooth relationships with other people, and recommends orange calcite as a charm for communication.