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A B C D E F G H I J
K L M N O P Q R S T
U V W X Y Z
- Cabochon a style of stone cutting with a dome-shaped top.
- Cacholong a bluish-white porcelain-like variety of opal.
- Cacoxenite quartz, usually amethyst, with radiating crystals of cacoxenite.
- Cairngorm a brownish-yellow variety of crystalline quartz found in the Cairngorm Mountains, Scotland.
- Calamine the name used in some English mineralogical books for the zinc carbonate Smithsonite, which see. In other works this name is used for a zinc silicate.
- Calcite R.I. 1-486 --- 1 651 S.G. 2-71 H. 3 Trigonal Colour, colourless and white, sometimes with grey yellow, blue, red, brown or black tints. Marble is a massive calcite, a fibrous form being known as "Satin-spar" and stalagmitic forms with well-marked banding are used for small objects and ornaments and are known under the MISNOMER ( COMMERCIAL LABEL )s: "Algerian onyx", "Mexican onyx" and "Oriental alabaster". Calcite of optical quality, known as Iceland spar, is used in the construction of Nicol prisms and in the dichroscope.
- Calcium titanate This compound has been synthesized and may appear on the market as a new gemstone. The material is colourless, orthorhombic, but near cubic, in crystallization. The hardness is 6 to 6l, the density 4-05 and the refractive index 2-40.
- Calibre-cut the term applied to stones cut to special shapes. Usually trap cut in style with sharp angular corners. The small square stones used for "eternity" rings are sometimes called calibre.
- Californite a massive variety of idocrase which simulates jade. See Idocrase.
- Callaite also Callaica, Callaina, and Callais earlier mineralogical names for turquoise, see Turquoise.
- Calorescence the term applied to the phenomenon exhibited by certain minerals which, when irradiated with heat rays produce visible light. See also Thermoluminescence and Luminescence.
- Cameo the term used to designate those stones, generally composed of two differently coloured layers, in one of which a raised figure or design is cut, while the layer of the second colour forms a background. Agates and certain sea shells are usually the materials used.
- Canada balsam a resin obtained from a species of fir and used as a mountant for microscopic specimens. R.I.= 1 53.
- Canada moonstone a name applied to the peristerite variety of feldspar. See Peristerite.
- Cancrinite R.I. approx. 1-51 S.G. 2-42 to 2-50 H. 5 to 6 Hexagonal Massive opaque yellow or orange. Gem locality is Canada.
- Canutillos the name by which good quality emerald crystals are locally known by the miners working the Colombia emerald mines.
- Cap-cut a fashioned stone in which the facets are irregular and haphazard. See Bastard-cut.
- "Cape emerald" a MISNOMER ( COMMERCIAL LABEL ) which has been applied to the mineral prehnite found in South Africa. See Prehnite.
- "Cape ruby" a MISNOMER ( COMMERCIAL LABEL ) for pyrope garnet found in association with diamond in South Africa.
- Cape stones a classification of gem diamond sub-divided into: fine silver Cape, silver Cape light Cape, Cape, dark Cape. This group is classified next in order to blue-whites and whites.
- Carat (precious metals)a term used to express the fineness of gold used in jewelry. It may be better understood as a twenty-fourth part, thus 9 carat gold contains 9 parts of pure gold and 15 parts of alloy, likewise 22 carat gold contains 22 parts of pure gold and 2 parts of alloy. The term is sometimes spelled Karat.
- Carat weight the unit of weight for diamonds and gemstones. It is defined as one-fifth of a gram (200 milligrams=0 200 gram). It became legal standard on the 1st of April, 1914, and was and frequently still is, known as the metric carat. The old London carat weighed 0.20530 gram, was not a legal standard and did not conform to the carat weight in other parts of the world, which varied in different countries from 0-1885 gram to 0-2135 gram.
- Carbon
- (1) see Carbonado.
- (2) black inclusions in diamond, often referred to as carbon marks.
- Carbonado an opaque, black, tough and compact variety of diamond found in Brazil, specific gravity being between 2-9 to 3-5. It is used for drilling Bits for deep boring and for slow running abrasive wheels.
- Carbon disulphide A liquid R.I. 1 63.
- Carborundum H. 9.5 S.G. = 3-17 a synthetic product made by heating coke and sand in an electric furnace. Used as an abrasive.
- Carbuncle a name for almandine garnet which has been cut en-cabochon.
- Carnelian see Cornelian.
- Cascalho the native name for the diamond-bearing gravel of Brazil.
- Casein a synthetic substance made from the albumen of milk and used occasionally as an imitation of amber and tortoiseshell and some ornamental stones. R.I. 1-55 to 1-56 S.G. 1-32 to 1-39 (usually 1-32 to 1-34.
- Cassia oil a vegetable oil akin to cinnamon oil. R.I.= 1 60.
- Cassiterite R.I. 1-997 --- 2- 093 S.G. 6-8 to 7-1 H. 6 to 7 Tetragonal Colours, red, brown, black and yellow Localities, Cornwall, Bohemia and Saxony.
- Castor oil a pale yellow oil obtained from the seeds of ricinus communis and used as an immersion medium in certain refractive tests. R.I.= 1-48.
- Cat's-eyes stones which, when cut en-cabochon, show a wavy changeable band of light across the dome. The phenomenon is known as "chatoyancy", and is often observed in quartz, chrysoberyl and tourmaline. See also Chatoyancy, Hawk'seye and Tiger's-eye.
- Cedar wood oil a vegetable oil used in immersion refractive index tests. R.I. = 1-51.
- Celestine (Celestite) R.I. 1-62 --- 1-63 S.G. 3-97 to 4-00 H. 3 to 3.5 Orthorhombic Colourless to bluish Locality U.S.A.
- Celluloid a thermo-plastic material made from a nitrocellulose base, sometimes used as an imitation of amber, etc. Two types:
- A-Ordinary celluloid (cellulose nitrate). R.I. 1-495 to 1-51 S.G. 1-36 to 1-80 (usually in the clear types 1-36 to 1-42.
- B-Safety celluloid (cellulose acetate). R.I. 1490 to 1505 S.G. 1-29 to 1-80 (usually 1-29 to 1-40)
- Cerussite R.I. 1-80 --- 2-1 S.G. 6-5 H. 3.5 Orthorhombic White, grey, green, blue and black. World wide occurrence.
- Ceylon diamond a MISNOMER ( COMMERCIAL LABEL ) for colourless zircon.
- Ceylonese chrysolite a MISNOMER ( COMMERCIAL LABEL ) for greenish-yellow tourmaline.
- Ceylonese peridot a MISNOMER ( COMMERCIAL LABEL ) for yellowish-green tourmaline.
- Ceylonite a dark green, almost opaque spinel, rich in iron sometimes used in jewelry. An alternative name for this variety is Pleonaste, see Spinel.
- Ceylon opal a MISNOMER ( COMMERCIAL LABEL ) for moonstone.
- C.G (Certified Gemmologist) suffix used by gemmologists who have qualified by the examination of the Gemmological Institute of America.
- Chalcedony a micro-crystalline variety of quartz , with the following varieties:Chalcedony common translucent with a white or bluish colour, green when containing chromium.
- Cornelian translucent flesh-red.
- Sard brownish red.
- Chrysoprase translucent apple green.
- 1-Plasma dark green with white or yellowish spots.
- 2-Bloodstone or Heliotrope dark green with scattered spots of red jasper.
- 3-Agates chalcedony where the colour is variously distributed, generally in parallel layers.
- 4-Banded agate colours in parallel bands.
- 5-Eyed-agate bands having a circular arrangement.
- 6-Fortification agate bands are angularly arranged.
- 7-Moss agate or Mocha stone containing dendritic inclusions. Agatised wood chalcedonic pseudomorph after wood.
- 8-Onyx similar to agate except that the bands are straight. Cameos are usually cut from these. Onyx, like all chalcedonies, can be stained, the black onyx nearly always has been so treated.
- 9-Sardonyx as onyx except that instead of the colours being black and white they are brownish red and white.
- 10 Jasper an impure variety of micro-crystalline quartz, opaque reds and browns also greyish blue and greens. Riband jasper is striped.
- 11 Hornstone a grey impure form which is sometimes stained to imitate lapis-lazuli. (This shows red under the colour filter whereas true lazurite does not.)
- The refractive indices and specific gravity of Chalcedony are but slightly lower than for Quartz.
- Chatham emerald (Chatham Cultured Emerald: Chatham Created Emerald) names applied at various times to an American synthetic emerald, grown by C. F. Chatham.
- Chatons paste (glass) stones backed with a reflecting foil.
- Chatoyancy (cat's-eye effect) is due to the reflection of light from fine fibres or fibrous cavities within the stone. The wavy band of light seen across the stone being at right angles to the direction of the fibres. To show this best stones must be cut en-cabochon. See also Asterism.
- Chatter marks see Fire marks.
- Chelsea colour filter
- Chemical composition the composition of a molecule of a substance, which may be an element or a combination of different elements in quantities which must obey certain definite chemical laws.
- Chemical composition of gem minerals See Chart
- Chemical elements matter composed of only one chemical type, and which thus cannot be decomposed into simpler substances by chemical means. See Chart
- Chessylite see Azurite.
- Chiastolite a variety of andalusite (which see) containing carbonaceous inclusions in the form of a cross
- Chicot pearls an alternative name for blister pearls. See Blister pearls.
- Chlorastrolite a greenish fibrous mineral related to prehnite. S.G. 3-2 H. 5 to 6 Colour, chatoyant green and white Locality, Lake Superior (U.S.A.).
- Chloromelanite a dark green nearly black ferruginous variety of jadeite. S.G. = 3-4. H. - 6.5 to 7.
- Chlorospinel see Spinel.
- Chondronite R.I. 1-60 --- 1-63 S.G. 31 H. 6.5 Monoclinic Yellow, red, brown