CIAMITA :
Spanish term for a blue Tourmaline.

CINNAMON GARNET :
Or cinnamite or cinnamon stone. Variety of or synonym of Hessonite of yellow to brown-orange to brown-reddish colour.

CITRINE :
Anciently sometimes called citron
Etym. : from the Latin ‘citrus’ meaning ‘lemon’ because of its colour.
Tectosilicate , member of the Quartz group.
Silicon dioxide.
SiO2 Traces of iron.
Natural citrine is quite rare, compared to the citrines obtained from treated gems (heated amethyst).
Physical and optical properties:
- Colours : very pale yellow to golden or brownish yellow, brown-orange (" madeira " colour) to brownish orange (coloration due to iron).
- Transparency : transparent
- Lustre : vitreous
- Hardness : 7
- S.G. : 2.65
- R.I. : 1.544 - 1.553 (Birefr : +0.009)
- Uniaxial positive.
- Pleochroism : very weak if natural, none if heated amethyst.
- Crystal system : trigonal.
- Fluorescence none.
- Cleavage difficult to none.
Occurrences :
Accompanies generally amethyst in the occurrences.
Brazil, Madagascar, Uruguay, Scotland.
Inclusions:
Straight growth zones or as chevrons.
Treatments :
The colour of citrine gets lighter at higher temperature and, when augmenting even more, becomes very pale and in the end becomes milky  (See Moonstone).
Most of the citrines on the market are heated amethysts (non dichroic and often with liquid inclusions giving the aspect of zebra skin).
The rock crystals of certain regions may ,by thermal treatments, become citrine coloured.
Confusions :
All the yellow stones among them yellow orthose from Madagascar, yellow topaz,  yellow sapphire or scapolite.
- Orthose sanidine (S.G. : 2.56; R.I. : 1.52 to 1.53; pale yellow).
- Scapolite (S.G. : 2.7 ; R.I. : 1.55 to 1.57 ; biaxial negative).
Imitations :
Yellow glass and synthetic corundum, doublets of yellow colour.
Synthetics :
- Russia produces a synthetic citrine of hydrothermal fabrication, that is very clean and only recognisable with infrared spectrography.
- Synthetic citrine is also produced in other countries.
See also :
- Topaz & citrine by J. Villod (TEC n°114 , 1956, page 149).
- Topaz & citrine (suite) by J. Villod (TEC n°115 , 1956, page 203).
- Gems of yellow colour (AFG n°30, page 7).

CITRINE PALMEIRA :
Prohibited Appellation for an Amethyst , heated , of a beautiful orange colour.

CLEOPATRA PEARLS :
Name of the two pearls that Cleopatra was wearing.
One was, according to Plinius, dissolved in vinegar which she drunk. The other is said to have been cut in two and  placed after her death on the ears of the statue of Venus in the Pantheon in Rome.

CLESOZOÏSITE :
Variety of epidote, light green to brown-green, poor in iron.
See epidote.
Collectors stone but not of gem quality.
Hydrated Borate of calcium
Ca₂B₆ . 5H₂O 
Physical and optical properties:
- Colours : milky-white
- Lustre : nacreous lustre on cleavage faces.
- Hardness : 4.5
- S.G. : 2.42
- R.I. : 1.586 - 1.614 (Birefr :  0.028).
- Crystal system triclinic.
- Dichroic.
Occurrences :
U.S.A.

CLINOZOISITE :
Variety of epidote with little iron content.
Ca₂Al₃[O|OH|SiO₄|Si₂O₇]
Physical and optical properties:
- Colours : light green, yellow
- orange, pink, greenish.
- Transparency : Transparent to translucent- Lustre : vitreous
- Hardness : 6 to 6.5
- S.G. : 3.37
- R.I. : 1.724 - 1.734 (Birefr. : 0.010).
- Biaxial positive.
- Crystal system monoclinic.
Occurrences :
Austria, Italy, Switzerland, Czechoslovakia, Mexico, Kenya (green-grey).

CLITORIS :
After Plutarchius : stone of black colour, found at Mount Lilea (India) that the inhabitants wear as earrings.

COBALTCALCITE :
Variety of Calcite with a lovely pink colour.

COBALTITE:
Or cobaltine (original spelling).
Sulpho-arsenide of cobalt.
Collector’s stone, very rarely cut.
CoAsS
Physical and optical properties:
Colours : silvery white with pink reflection, steel grey or slightly violet.
Transparency : Opaque
Hardness : 5.5
S.G. : 6 to 6.33
Crystal system cubic.
Occurrences :
England, Canada, Scandinavia, Russia, U.S.A., Sweden, Norway

COCCOLITE :
Variety of Diopside.

COCKLE :
Ancient term designating several minerals forming long prisms, dark green or black, generally tourmaline, sometimes hornblende.

COERULCOLACTITE :
Synonym for Turquoise.

COLEMANITE :
Hydrated borate of calcium.
 Collectors stone, not of gem quality.
Ca₂B₆O₁₁.5H₂O
Physical and optical properties:
- Colours : white
- Transparent with vitreous lustre ; sometimes nacreous, milky white with nacreous lustre on cleavage surfaces.
- Hardness : 4.5
- S.G. : 2.42
- R.I. : 1.586 to 1.614 (Birefr. : 0.028).
- Biaxial negative.
- Crystal system monoclinic.
- Fluorescence whitish or green.
Occurrences :
U.S.A. (Death Valley, California ; Clark County, Nevada).

COLLOPHANITE :
Or colophonite.
To some: Prohibited appellation for black Melanite Garnet
To others : Variety of andradite garnet, of brown-black or brown-yellowish colour.

According to certain authors also used for a variety of idocrase.

COLORADO JADE :
Prohibited Appellation for Amazonite.

COLUMBITE :
(Fe,Mn) (Nb,Ta)₂ O₆
Physical and optical properties:
- Colours : black
- Opaque with semi-metallic lustre
- Hardness : 6
- S.G. : 5.2 to 8.0
- R.I. :
- Crystal system orthorhombic.

COMMON OPAL:

Opal having basically only a mineralogical value, containing but very little or none at all precious opal

COMPTONITE :
Opaque variety of Thomsonite from the region of Lake Superior (also found in Italy) that, cut as cabochon, are stones for collectors.

CONNEMARA or CONAMARA :
A rock composed of marble and Serpentine ,from England, of green-grey to dark green colour, sometimes yellowish green and used as an ornamental stone .

CONICALCITE :
Synonym : conichalcite.
 Collectors stone, not of gem quality.
Arsenate of copper of grass-green colour.
CaCu[OH|AsO₄]
Physical and optical properties:
- Opaque with greenish colour, resembling Malachite.
- Hardness : 4.5
- S.G. : 4.12
- R.I. : 1.778
Confusion the most probable : 
Malachite  but its colour is more bluish.
Occurrences :
California.

COPAL :
Natural fossil resin containing succinic acid, but poorer in oxygen than amber.
Copal is often used to imitate Amber.
Physical and optical properties:
- Colours : yellow-orange, orange.
- Hardness : variable
- S.G. : 1.06
- R.I. : 1.54

Occurrences :
Africa, East Indies, South America

COPPER MALACHITE :
Prohibited Appellation for chrysocolla

COQUILLAGES:
" Sur l'utilisation des coquillages ", by Franck Guilbert (AFG n°10, page 11).

CORAL:
Etym. : from the Greek ‘korallion’
Calcareous arborescent squeletton of Coralium Nobile on which live small polyps.
Carbonate of calcium.
Ca CO₃ + magnesium and organic substances.
Physical and optical properties:
- Colours : blood-red, orangy red, vivid red to pale pink + pink the colour of skin (‘Angel skin’)
- Transparency : Opaque with sometimes a slight translucency in thin sections
- Hardness : 3 to 4
- S.G. : 2.6 to 2.7
- R.I. : 1.486 to 1.658.
- Microcrystalline stone (fibrous construction, sometimes undulated).
- amorphous.
- Fluorescence dark purple almost none.
- Fracture : irregular to splintery.
- Cleavage none
- Characteristic structure with loupe (traces of longitudinal channels, traces of lateral growth secretions).
Occurrences :
Italy, Japan, Australia, Persian Gulf, Malaysia, Spain, Canary Isles, Isle of Cap Verde, Red Sea, U.S.A., ...
Treatments :
Coral being porous, dying is easily applicable and must disclosed.
Imitations :
Coral has often been imitated by :
- Corozo (nut from an American tropical tree) (S.G. : 1.40 to 1.43 ; R.I. : 1.54 ; structure in dots and lines very characteristic).
- Dyed bone and ivory  (S.G. : 1.7 to 1.9 ; R.I. : ± 1.54; channels with ramifications standing out clearer due to dye visible to with loupe).
- Glass and coloured porcelain (S.G. and R.I. variable).
- Plastic (S.G. : 1.25 to 1.45 ; R.I. variable ; traces of moulding at the sides).
- Powder of coral assembled with resin (melts with test of red-hot needle).
Red and pink coral presents lines of colour alternating more vivid or more pale, which allows la identification of true coral from its different imitations.
Confusions :
- Pink pearl " Strombus gigas " (S.G. : 2.7 ; structure like flames).
See also :
- Imitation von weißer Koralle (ZDG n°41 , 1962, page 24).
- Schwarze Koralle von Australien (ZDG n°58 , 1966, page 29).
- Abenteuer mit Koralle , by Robert Fitzgerald (ZDG n°64 , 1968, page 30).
- Le corail en Italie (TEC n°173 , 1960, page 637).
- (TEC n°174 , 1961, page 9).
- Le corail en Italie, suite et fin (TEC n°175 , 1961, page 59).
- Bijouterie de corail noir (TEC n°263 , 1968, page 384).
- Les récifs de corail menacés d'extinction (TEC n°282 , 1970, page 43).
- S.O.S. récifs de corail (TEC n°284 , 1970, page 155).
- Le corail noir (TEC n°303 , 1971, page 555).

CORALINE :
Chalcedony of red-aniline colour.

CORDIERITE :
Synonym : Iolite or Dichroite.

CORENCITE :
Synonym of Chloropal.

CORUNDUM :
Oxide of aluminium.
Al₂O₃
Physical and optical properties:
- Colours : Colourless when pure (rare), coloured by ions of transition elements.
Red = ruby (colouring element Cr2O3, for Thailand Cr2O3 + Fe2O3)
Ruby Burma = pure red, ‘pigeon blood’.
Ruby Thailand = darker red to brownish red.
Ruby Sri Lanka = red more light, and softer (pink : pink sapphire).
Blue = sapphire (colorant TiFeO3).
Burma Sapphire = nice blue, royal blue, indigo blue.
Thailand Sapphire = dark to light blue.
Cachemire Sapphire = blue, ‘peacock blue’, often hazy appearance.
Sri Lanka Sapphire = light blue, blue slightly violet, greyish blue.
Montana Sapphire = pure blue to dark, metallic lustre.
Australian Sapphire = blue-green very dark.
Orange-pink = padparadscha.
Green, yellow, pink, purple, violet, black Sapphire.
Star Ruby, star sapphire, cat’s eye sapphire.
Alexandrite type Sapphire (blue in natural light - violet under artificial light)
- Hardness : 9. Corundum is made up of aluminium and oxygen. The electrical field of aluminium is high and the distance aluminium/oxygen is narrow, which provokes an electrovalent reaction Al+++/O- of very great strength. Thanks to this phenomena, corundum is the hardest mineral after diamond.
- S.G. : 4 (± 0,03).
- R.I. : 1.760 - 1.770 ( Birefr : 0.008 to 0.009).
- Uniaxial negative.
- Crystal system trigonal.
- Dichroism : Ruby : violet red / yellowish red.
Green : bluish green / yellowish green to greenish yellow.
Blue : blue / light blue to yellowish blue.
Violet : violet red / yellowish red.
Yellow : very weak.
Pink : visible.
- Cleavage : none,  but separation planes exist, perpendicular to the ternary axis and also part in three possible directions of the rhombohedron.
- Corundum is a good thermal conductor.
Occurrences :
In metamorphic rocks of high pressure or sedimentary rocks rich in aluminium. May be accompanied by spinel, green zoisite or amphibole.
More specifically:
- Myanmar : Mogok : ruby / Kathe : sapphire.
- Cachemire : Sapphire.
- Sri Lanka : sapphire blue, pink, purple, yellow, brown and star stones.
- Thailand : ruby, sapphire.
- Kenya : ruby, often opaque.
- Tanzania : ruby (opaque in massive green zoisite), sapphire.
- U.S.A., Australia : sapphire blue, yellow, green, a few rubies in Queensland.
- Norway : ruby.
- Madagascar : ruby and sapphire (all colours).
Inclusions :
Sometimes, titanium is present under the form of rutile needles intersecting at 60°.
When they are not so numerous, the light traversing the stone is diffused, provoking a phenomena of ‘silky appearance’ in the stone.
When they are more numerous, the stone shows a star effect when cut.
Inclusions more specific :
- Ruby Myanmar :
 rutile needles intersecting at 60° and 120° perpendicular to the optic axis, generally very small and short but quit dense.
Crystals of corundum - zircon - garnet - rutile - spinel (often well developed octahedrons) - mica (platelets).
- Ruby Thailand :
Very dark inclusions with hexagonal and triangular form, often green in colour.
Liquid filled channels, sometimes straight.
Polysynthetic twinning lamellae  with boehmite needles on intersections.
- Ruby Sri Lanka :
Solid inclusions, liquid and gas filled cavities.
Well formed rutile needles, generally longer than those of Myanmar.
Zircons with tension halo.
Crystals of muscovite, corundum, hematite, garnet.
Liquid droplets = healing fractures in wing-like shapes.
- Sapphire Cachemire :
Foggy lines or zones with angles 60° and 120°.
Liquid inclusions in healed fractures with colorations zones of yellowish and brownish colour– inclusions of green tourmaline.
- Sapphire Myanmar :
Rutile needles like in ruby.
Big crystals of rutile.
- Sapphire Thailand :
No rutile needles.
Inclusions of channels, liquid filled and linked together.
Brownish substances (probably iron).
- Sapphire Sri Lanka :
Rutile needles, longer than in those from Myanmar.
Liquid filled channels, short or elongated, but not linked as in those from Thailand, certain containing two-phases.
Crystals of zircon with halo ; garnet ; spinel ; mica ; hematite ; calcite ; corundum.
Long, well profiled negative crystals.
- Sapphire Montana :
Opaque crystals; large irregular inclusions liquid
Long liquid filled channels.
- Sapphire Australia :
Liquid inclusions.
Strongly pronounced zones of coloration.
Confusions :
Benitoite, Tanzanite, Cordierite, Spinel.
Imitations :                                            
- artificial glass (also asterism : star engraved on backside cabochon).
- Doublet (synthetic colourless corundum /synthetic ruby or sapphire ; natural sapphire / synthetic ruby)
- Triplet : corundum - or synthetic colourless spinel / glass engraved with a star/ glass.
- Cabochon of natural asteriated quartz with bottom covered with blue or red enamel.
- Synthetic star corundum from Linde Air Products Company (since 1947), the base of these American stones is not polished.
Synthetics : some early history :
In 1877, French chemist E. Frémy in collaboration with C. Feil, worked on the problem of ruby synthesis and produced rubies and other colours of corundum ; the artificial ruby was coloured as is the natural by chromium oxide, while the artificial sapphire has cobalt oxide as colouring element.
Later, towards 1890, Auguste Verneuil came to replace C. Feil with Frémy and made the work progress. In 1891, Frémy published a report on this synthesis in his book : " Synthesising ruby ".
In 1902, Verneuil publishes his procédé worldwide, known under the name procédé Verneuil (Verneuil Oven). This procédé is sometimes called " flame fusion process ".
In 1947, on adding a percentage of titanium oxide and a treatment at high temperature on one obtained sapphire showing asterism. Afterwards also star ruby was produced, as well another colours of star corundum. One heats the ‘pear’ of synthetic material to 1100°C, this produces the precipitation of titanium (titanium oxide is added from 0,1% to less than 0,3%). This titanium oxide presents itself as planes of rutile needles with trigonal arrangement.
A part of the pear cut as cabochon showed a star, the other part not (concentration of 2/3 or ¾ of the pear) the rest of the pear showed the same characteristics as pure synthetic ruby.
The more recent American productions offered opaque star corundum and showed more pronounced colours.
See Synthetics.

See also Gemmological News concerning corundum.

CORNALINE :
French for cornelian. Or carneol.
Variety of Chalcedony of red-orange to red-brown, brique red colour.
Group of the micro-crystalline quartzes.

CORNE D'AMMON :
After Plinius : gem from Ethiopia of golden colour.

CORNELIAN :
Or carneol.
Variety of Chalcedony of red-orange to red-brown colour.
Group of microcrystalline quartz.
SiO2.
Physical and optical properties:
Colours : from pink flesh colour to red brown
- Hardness : 6.5
- S.G. : 2.57 to 2.64.
- R.I. : 1.525 to 1.545 (Birefr : 0,004).
- Crystal system trigonal (fibrous aggregates).
- Cleavage none.
- Fluorescence bluish white.
Occurrences :
India, Yemen, Brazil, Uruguay.
Imitations :
The greater part of cornelian on the market are chalcedonies dyed with iron salts.
Fire opals become cornelian  by silification.
Treatments :
This stone is heated to intensify its colour.

CORNISH DIAMOND :
Prohibited appellation Name given by the English to a Rock crystal.

CORONITE :
Synonym of magnesium containing Tourmaline.

CORUNDITE :
Or corindite.
Prohibited appellation for a synthetic corundum, used as an abrasive.

CORUNDOLITE :
Term given by the English to a colourless synthetic corundum or to a colourless synthetic spinel.

COTTERITE :
Variety of quartz with nacreous lustre.

CRAPAUDINE :
Synonym for Odontolite.

CREEDITE :
Collector’s stone
Ca₃Al₂SO₄ (F,OH)₁₀ . 2 H₂O
Physical and optical properties:
- Colours : white, colourless, violet
- Transparency : transparent
- Lustre : vitreous
- Hardness : 3.5 to 4
- R.I. : 1.461 - 1.485 (birefr; : 0.024)
- biaxial negative
- cleavage : perfect- Crystal system : monoclinic

CREOLITE :
Jasper of Shasta & San Bernardino Counties in California, of red and white colour.

CRISPITE :
Synonym of Rutile.

CRISTAL DE BOHEME :
French. Also called ‘cristal de plomb’.
Glasses of different types in the fabrication of which enters lead.

CROCIDOLITE :
Synonym : Krokydolite.
(In the stone tiger’s eye the fibres altered into brown-yellowish have been replaced by quartz).
Fine fibrous variety of Riebeckite.  Etym. : for Emil Riebeck (1853-1885), German explorer.
Na₂(Fe²⁺,Mg) ₃Fe ₂³⁺ [(OH|F)Si₄O₁₁]₂
Physical and optical properties:
- Colours : blue.
- Hardness : 4
- S.G. : 3.2 to 3.3
Occurrences :
South Africa.

CROCOITE :
Collector’s stone.
Pb[CrO₄].
Physical and optical properties:
- Colours : hyacinth red, orangy red, orange, yellow.
- transparency : transparent to translucent
- lustre : adamantine to vitreous
- Hardness : 2.5 to 3
- S.G. : 5.9 to 6.1.
- R.I. : a : 2.29 – 2.31 / b : 2.36 / g : 2.66 (Birefr. : 0.270 to 0.350).
- Biaxial positive.
- Crystal system monoclinic.
- Cleavage distinct.
- Fluorescence weak reddish or brownish under L.W.U.V., more pronounced under S.W.U.V.
Occurrences :
Australia (Tasmania), Russia (Ural), Rumania (Rezbanya), Brazil (Ouro Petro), U.S.A. (Arizona).

CROISETTE DE BRETAGNE :
French for cross stone

CROSS STONE :
Used as synonym for Staurotide twinned in the form of a cross, or Chiastolite.

CROWN OF THE ANDES :
Crown set with 453 emeralds weighing 1523 carats with, in the centre, an emerald of 45 carats.

CRUCILITE :
Synonym for cross stone.

CRYOCONITE :
Mixture of garnet, sillimanite, zircon, pyroxene, quartz,…

CRYSTOLON :
Commercial name for an artificial corundum.

CUARZO :
Synonym of Quartz.

CUBIC ZIRCONIUM :
Synthetic stone imitating Diamond.

CUIVRE CARBONATE BLEU :
French. Synonym for Azurite (de Beudant).

CUIVRE CARBONATE VERT :
French. Synonym for Malachite.

CUIVRE HYDROSILICIEUX :
French. Synonym for Chrysocolle.

CULTURED PEARL :
Pearl of which the formation and/or the volume is due to human intervention.

Physical and optical properties : same as (natural) pearl
S.G. : 2.70 to 2.90
Hardness : 2.5 to 4

CUIVRE SILEX :
French. Synonym of Chrysocolla .

CUMMINTONITE :
Synonym of Rhodonite.

CUPRITE :
Etym. : from the Latin ‘cuprum’ after its composition (name given in 1845)
Collector’s stone.
Cu₂O.
Physical and optical properties:
- Colours :  red
- Transparency : Transparent
- Lustre : adamantine to sub-metallic
- Hardness : 3.5 to 4
- S.G. : 5.85 to 6.15
- R.I. : 2.85
- Crystal system cubic
Occurrences :
New Mexico.

CYANEE :
Or cyanos.
Ancient denomination for Lapis-lazuli

CYANITE :
Synonym for Kyanite .

CYANOCHALCITE :
Variety of Chrysocolla.

CYMOPHANE :
Or Cymophanite.
Synonym of Cat’s eye Chrysoberyl.

CYPHOÏTE :
Variety of Serpentine.

CYPRINE :
Variety of idocrase , blue from Norway; bluish and reddish found near the Vesuvius, Italy.