CEDARITE :
Fossil resin resembling amber from Canada.

CELESTIAL OPAL :

Prohibited Appellation for a moonstone .

CELESTINE :
Synonym : Celestite.
Sulphate of strontium.
Sr[SO₄].
Collectors stone, rarely cut.
Physical and optical properties:
- Colours : colourless to bluish, orange, greenish, blue with colourless zones, red-brown

- Transparency : transparent

- Lustre : vitreous
- Hardness : 3 to 3.5
- S.G. : 3.96 to 4.00
- R.I. : 1.623 - 1.635 (Birefr. : 0.009 to 0.010)
- Biaxial positive.
- Crystal system : orthorhombic.
- Cleavage in two directions.
- Fluorescence : whitish to bluish white.
Occurrences :
Sicily, Switzerland, Italy, Great Britain, U.S.A., South-West Africa, Canada (for the orange coloured gems).

CERACHAT :
German name. Variety of Chalcedony.

CERANITE :
Or Ceranhite.
Synonym of Nephrite.

CERASITE :
Cordierite with carboniferous inclusions.

CERKONIER :
German term designating a colourless zircon.

CERULEN :
Name given to a variety of calcite coloured green or blue by malachite or azurite.

CERUSSITE or CERUSITE:
Collector’s stone.

Carbonate of lead.
PbCO₃ 
Physical and optical properties:
- Colours : colourless, blue, green (coloured by Cu) and white, grey, black.

-Transparency : Transparent for the colourless ones, translucent for the blue, green and white  ones
- Hardness : 3 to 3.5
- S.G. : 6.46 to 6.57
- R.I. : 1.804 - 2.078 (Birefr. : 0.274)
- Biaxial negative.
- Crystal system : orthorhombiqc.
- Fluorescence pale blue or green under S.W.U.V., different tints of yellows under L.W.U.V.
Occurrences :
Namibia, Tunisia, Morocco, U.S.A.

CEYLANITE
Original spelling of ceylonite.

CEYLONITE :
Synonyms : ceylanite ; pleonaste .

Variety of Spinel , dark green and containing some iron.
Aluminium oxide of magnesium and iron.

(Mg,Fe)Al₂O₄
Physical and optical properties:
- Colours : Different tints of dark green sometimes almost black, dark brown, rarely dark blue seemingly black.
- Hardness : 8
- S.G. : 3.63 to 3.90 (higher than " ordinary " spinel: 3.58 to 3.61)
- R.I. : 1.77 to 1.80 (higher than " ordinary " spinel: 1.712 to 1.736)
- Fluorescence weak reddish.
- Crystal system : cubic (octahedrons, rhomboidal dodecahedrons, twins).
- Cleavage : imperfect.
Occurrences :
Myanmar, Sri-Lanka, Brazil, Thailand, USA.
Synthetics :
Dark green synthetic spinel - also produced to imitate different gems. (recognition : phantom images under polariscope, R.I. superior to stones imitated,…).
Confusions :
Aquamarine, chrysoberyl, garnet, ruby, sapphire, topaz, blue zircon. The most easy feature to distinguish spinel from these other stones is the fact that spinel is singly refractive.

CEYLON RUBY:

Old name for ruby from Sri Lanka . Equally a prohibited appellation for an almandine garnet .

CHACHIGUITE :
Or chalchuite, chalchuhuite.
Mexican terms designating all green opaque or semi-opaque stones, especially green turquoise,  smithsonite or jade.

CHALCEDONY :
Fibrous crypto-crystalline silicate, belonging to the quartz group.
SiO₂.
Group of the chalcedonies : agate, cacholong, chrysoprase, cornelian, heliotrope, jasper, plasma.
Physical and optical properties:
- Colours : milky aspect (pure), when coloured by iron or nickel => grey, bluish,… ; red = cornelian ; green = chrysoprase ; brown = sardonyx.
When containing nickel and of green colour the name is : chrysoprase ; when chrome is the green colouring element, it’s name is green Agate ; when distinctly reddish, it is called Chalcedony ; sardonyx when brown-red and onyx when it is completely black.

- transparency : Translucent to opaque.
- Hardness : 6.5 to 7
- S.G. : 2.57 to 2.64
- R.I. : 1.530 - 1.540
- Birefr. : 0.007 (not always observable).
- Uniaxial positive.
- Crystal system : trigonal (aggregates  fibrous).
- Cleavage none.
- Bluish (or other colours) white fluorescence according to the trace-elements.
Occurrences :
Uruguay, Brazil, … almost always associated with agate.
Great-Britain, Madagascar, India, China, Japan, Colombia, U.S.A., Germany, …
Treatments :
The vast majority of the chalcedonies on the market are dyed thanks to their great porosity.
Chemical treatment is also used. In fact, chalcedony, soaked in a sugar solution, is afterwards submerged in chlorhydric acid to become yellow ; in an iron sulphate to become red ; in ferro-cyanide to become blue ; in a nickel solution to become apple-green and in a solution a chromium solution for it to take on a vivid silvery sheen.
Confusions :
- Green  common Opal (S.G. : 2.0 to 2.5 ; R.I. : 1.45 ; imitates chrysoprase).
- Agate dyed green (S.G. : 2.6 ; R.I. 1.53 ; microcrystalline ; imitates chrysoprase).
- Aventurine green (S.G. : 2.6 ; R.I. : 1.55 ; imitates chrysoprase).
- Jade (S.G. : 3.33 ; R.I. : 1.66 ; microcrystalline ; imitates chrysoprase).
- Glass and dyed plastics (S.G. and R.I. variable ; bubbles and traces of fusion).
Prohibited appellations :
- Blue dyed agates are improperly sold under the name of chalcedonies.
See also :
- Elektronenmikroskopische Untersuchungen an Chalcedon und Edelopal , by J. Pense (ZDG n°50, 1964, page 25).
- Neu entdeckter grüner Chalcedon (ZDG n°60 , 1967, page 36).
- Les gemmes et les pierres ornementales du Maroc, by J. E. Dietrich and M. Saadi (AFG n°19, page 12).

CHALCOPHONE :
Name given by Plinius to a mysterious black coloured stone.

CHALCOPYRITE :
Etym. : from the Greek "chalkos", copper, and "pyrites", strike fire.

Collector’s stone

CuFeS₂  
Physical and optical properties:
- Colours : Yellow to bronze-yellow
- Transparency : opaque
- Lustre : metallic.
- Hardness : 3.5 to 4
- S.G. : 4.2
- R.I. :
- Crystal system : tetragonal

Occurrence :

A major ore of copper (the most abundant). Common in sulfide veins and disseminated in igneous rocks.
Confusions :
Pyrite (chalcopyrite is of a deeper yellow colour).

CHALCOSITE :
Synonym : chalcosine (or chalcocite).

Etym. : from the Greek ‘Chalkos’ meaning ‘copper’.
Sulphide of copper.
Stone rarely cut except when inter-grown with Amazonite.

Cu₂S
Physical and optical properties:
- Colours : grey, blue-black, black
- Transparency : opaque
- Lustre : metallic
- Hardness : 2.5 to 3
- S.G. : 5.5 to 5.8
- Crystal system : monoclinic
Occurrences :
Madagascar.

CHALCOSTAKTITE :
Synonym of Chrysocolla.

CHALKOPISSITE :
German term. Mixture of Chrysocolla and Limonite.

CHAMBERSITE :
Etym. : after the location where it was first found in 1962, Chambers County, Texas
Collector’s stone.
Borate (tectoborate).
Mn₃[Cl|B₇O₁₃]
Physical and optical properties:
- Colours : Colourless to dark purple.
- Hardness : 7
- S.G. : 3.49 to 3.50
- R.I. : 1.732 - 1.745 (Birefr. : 0.010 to 0.012)
- Biaxial positive.
- Crystal system : orthorhombic (pseudo-hexagonal).
Occurrences :
Barbers Hill & Chambers County, Texas, U.S.A.

CHAMELEONITE :
Variety of Tourmaline of olive-green colour in natural light and brownish-red in artificial light.

See also :
Turmalin changierend (ZDG n°50 , 1964, page 35).

CHARLES II SAPPHIRE :
Synonym for the Stuart Sapphire.

CHARLES II PEARL :
Pearl discovered in 1691, presumably in the Americas and presented to Charles II.
With " La Peregrina ", a pearl of almost equal weight, worn in earrings by the Queens of Spain.

CHAROÏTE :
Synonym : tscharoïte.
Charoïte is the major constituent of a rock constituted of a mass of intermingled fibres.
Hydrated silicate of potassium, calcium and sodium.
K(Ca,Na)₂[(OH,Fe)Si₄O₁₀]. H₂O
Physical and optical properties:
- Colours : purple to violet.
- Transparency : opaque.
- Hardness : 5 to 6
- S.G. : 2.54
- R.I. : 1.550 – 1.559 (Birefr. : 0.009)

- Biaxial positive
- Crystal system : monoclinic (hard and fibrous aggregates).
Occurrences :
Is found at the contact of calcareous metamorphic rocks, associated to pyroxenes and to feldspars; only known location : East Siberia, Yakut Republic, Russia.
Confusions :
Amazonite, aventurine, californite, chrysoprase, grossular, jasper plasma, prase, prehnite, serpentine, smithsonite,
Imitations :
- Doublets, triplets.
- tinted jade
Supplementary information on the imitations of charoïte :
- During a voyage in Alaska, a member of the GIA procured two kinds of imitations of charoïte.
One was called" Royal Russianite ", consisting of a bracelet of 20 pearls of 8,1 mm.
The two kinds had the following physical characteristics  :
- R.I. : 1.55 ( !!! identical to natural charoïte !!!).
The test with a heated needle gave the smell of plastic and under the microscope, the texture revealed itself as " unnatural ".
G & G Winter 1999 p121.

CHATHAM :
See synthetics.

CHATHAM EMERALD :
Prohibited appellation for a synthetic emerald fabricated by the firm Chatham.

CHATON :
French. Name given to a glass with a coloured thin metal sheet under the pavilion. .

CHAUX FLUATEE :
French. Synonym of Fluorite.

CHELMSFORDITE :
Synonym for Scapolite.

CHEMAWINITE :
Fossil resin of pale yellow to dark brown colour, found in the N. Saskatchewan River of Canada (S.G. : 1.055).

CHERRY OPAL :

Variety of fire opal from Mexico , translucent, of cherry red colour

CHESSYLITE:
Synonym for Azurite.
Azurite extracted at Chessy (Department of the Rhône in France).

CHEVEUX DE VENUS :
French term designating the needles of Rutile in certain quartzes, like filaments resembling golden blond coloured hair.

CHIASTOLITE :
Variety of Andalousite , with carboniferous inclusions disposed in the form of a cross (Kreuzstein in German).

Al₂(SiO₅)
Physical and optical properties:
- Colours : the colour variable (whitish, grey, yellowish to brownish).

- Transparency : opaque to translucent
- Hardness : 5 to 5.5 (andalousite = 7.12).
- S.G. : 3.12 to 3.18 (idem andalousite).
- R.I. : 1.641 - 1.648 (Birefr : 0.011 to 0.016) (± idem andalousite).
- Dichroism distinct : green-yellow, green, brownish green.
- Fluorescence none.
- Spectrum : 2 intense absorption lines in the extreme red as well as 2 others in the orange part.
Occurrences :
Australia, Bolivia, Chile, Spain, USA, France, Russia.
Inclusions :
Carboniferous cruciform inclusions.
Confusions :
This stone can not be confounded with any other stone thanks to its characteristic design in the form of a cross.
See also :
Some rare Materials by W. F. Eppler (TJG Vol. 12, n°7 of 1971, page 256).

CHI KU PAI JADE:
Term given by the Chinese to a Jade thermally treated to modify its colour.

CH'ING YU :
Chinese name for a red Jade of acceptable quality.

CHILIAN LAPIS or LAPIS from CHILE :

Variety of lapis lazuli of blue colour more pale than the lapis lazuli from Afghanistan and strongly  veined with matrix of white calcite

CHINESE CAT’S EYE :

Is cut from a shell of brown, yellow or green colour.

CHINESE JADE:
Synonym for Jadeite.
Equally a Prohibited Appellation for a serpentine.

CHINESE OPAL :

Prohibited Appellation for a chalcedony .

CHINESE TURQUOISE :

Prohibited Appellation Term rarely used to designate an obsidian, steatite, calcite or quartz tinted blue .

Genuine turquoise from China .

CHIZEULITE :
Synonym for Andalousite.

CHLORAPATITE :
Apatite with dominating chlorine content.

CHLORASTROLITE or CHLORASTOLITE:
Synonym for or variety of pumpellyite (green star stone. First discovered on Isle Royal, Lake Superior by C. T. Jackson and J. D. Whitney in 1847; state gemstone of the State of Michigan , USA)

Fibrous and chatoyant.
Ca₂MgAl₂[(OH)₂|SiO₄|Si₂O₇].H₂O
Hydrated silicate of aluminium and calcium and magnesium.
Resembling very strongly malachite.
Physical and optical properties:
- Colours : different shades of light to dark yellow-green, designs of green a little more greyish tinted than in malachite.

- Transparency : opaque, superficially translucent (with chatoyant effect)
- Hardness : 5 to 6 (3.5 to 4 for malachite).
- S.G. : 3.1 to 3.5 (3.8 to 4.1 for malachite).
- R.I. : average (spot) 1.66 to 1.7 (1.85 for malachite).

- Crystal system : monoclinic
Occurrences :
Almost exclusively coming from near Lake Superior, Michigan, U.S.A.

CHLOROMELANITE :
Etym. : from the Greek ‘khloros’ = green and ‘melas’ = black.

Variety of Jadeite , intense dark green spotted with black.

In the composition of this variety of jadeite, the aluminium component is for a large part replaced by iron causing the colour to darken significantly.
Physical and optical properties:
- Colour : dark green to black.
- Hardness : 6.5 to 7
- S.G. : 3.25

- Crystal system : tetragonal.

CHLOROPAL :
Opal of green colour resembling a hydrated iron-silicate.
Fe³⁺Si₃O₉.5H₂O (Source Dana).

CHLOROPHANE :
Variety of Fluorite becoming fluorescent green when heated.

CHLOROPHYLLITE :
Alteration of Cordierite.

CHLOROSPINELLE :
Variety of spinel, dark green containing magnesium and zinc.
(Mg,Zn)OAl₂O₃
Occurrences : Russia.

CHLOROSAPPHIRE :
Variety of Corundum , green in colour.

CHLOR-UTAHLITE :
Synonym of Uthalite.

CHONDRODITE :
Silicate of magnesium with fluorine.
2[Mg₅Si₂ O₈(F,OH)₂]
Rare, collectors stone.
Physical and optical properties:
- Colours : yellow, brown, red-brown, red
.- Transparency : Transparent to translucen
t- Lustre : vitreous
- Hardness : 6 to 6.5
- S.G. : 3.1 to 3.2
- R.I. : 1.590 to 1.640 - 1.62 to 1.64 (birefr. : 0.027 to 0.032)
- Biaxial positive.
- Crystal system : monoclinic.
- Fluorescence weak orange under L.W.U.V. and inert under S.W.U.V.
- The term chrondrodite has also been given to a red garnet.
Occurrences :
U.S.A., Sweden.
Remarks :
Under this name, one also designates a dark red garnet found at Putnam, New York in the U.S.A.. Eppler mentions it as a synonym for peridot.

CHONEUTICIT :
Variety of Fluorite.

CHORLO :
Spanish term for Tourmaline.

CHRYSOLITE CAT’S EYE :

Prohibited Appellation for a chrysoberyl cat’s eye

CHRISOTITE :
Synonym of Ceylonite.

CHROME-CEYLONITE :
Synonym of Picotite.

CHROME-DIOPSIDE :
Variety of Diopside , chromiferous and of very dark green colour.

CHROME-KYANITE :
Variety of kyanite , chromiferous.
(Al,Cr)₂SiO₅

CHROMIFEROUS GARNET :
Used as synonym of uvarovite.

CHROMITE :
Mineral belonging to the group of the spinels.
Oxide of iron and chrome.
Cr₂FeO₄
Physical and optical properties:
- Colours : blackish brown to brown.
- Transparency : Opaque
- Lustre : metallic
- Hardness : 5 to 5.5
- S.G. : 4.1 to 4.9 (generally 4.5 to 4.8)
- R.I. : 2.08 to 2.16
- Crystal system : cubic
- Slightly magnetic
- Cleavage none
Occurrences :
U.S.A., Austria, France, Asia Minor, South Zimbabwe, New Caledonia,…
Inclusions :
In fact, chromite is often present as an inclusion.
This type of inclusion is especially found in jades and in massive green garnets, so much so as to make it a diagnostic feature.

CHROMOJADEITE :
Variety of Jadeite riche in chrome.
The variety most chromiferous of Chromojadeite is called Tawmanite.
Physical and optical properties:
- Colours : intense green often dark with veined nuances visible in transparency.
- Transparency : Translucent
- R.I. : 1.68 (1.640 to 1.673 for Jadeite).
- becomes slightly reddish under the Chelsea filter whereas jadeite becomes more explicit reddish.

CHRYSANTHEME :
Or  Chrysanthemum stone.
Synonym for Kikukwaseki.

CHRYSOBERYL :
Oxide of aluminium and beryllium.
Al₂[BeO₄]
The chrysoberyl group comprises :
- chrysoberyl
- alexandrite
- cat’s eye Synonym : Cymophane
Physical and optical properties:
- Colours : when aluminium and beryllium are partly replaced by iron, then the stone can adopt the colours green-yellow, golden yellow, yellow brown, olive-green , grey-green, colourless to brownish and its name is chrysoberyl.
When there is replacement of the aluminium by chrome, the stone is called alexandrite and shows a green colour in daylight (grass-green to deep green, or dark olive-green), against red in artificial light (strawberry red to dark, or brownish red).                                                 Concerning cat’s eye chrysoberyl, fine channels running parallel produce a luminous narrow band of silvery white that seems to glide over the surface of the stone.

- Transparency : transparent
- Lustre : vitreous
- Hardness : 8.5 (the hardest stone after corundum)
- S.G. : 3.70 to 3.72.
- R.I. : 1.744 - 1.755 (Birefr : +0,009).
- Biaxial positive.
- Crystal system : orthorhombic.
- Cleavage imperfect.
- Dichroism :
-          Chrysoberyl : colourless / pale yellow / citron yellow.
-          Cat’s eye : weak : green / citron yellow / reddish yellow
-          Alexandrite :Ural : profound red / yellow orange / green blue
                 Sri Lanka : red / orange / green
                 Mogok : purple / grass green / green blue
                 Brazil : dark red / orangy yellow / green
- Chelsea filter : red for alexandrite.
- Spectrum :                                                                                                                                   - Chrysoberyl : absorption lines at 504nm, 495nm 485nm and a broad band centred at 445nm.
- Cat’s eye : one broad band at 445nm.
- Alexandrite : band between 680nm & 670nm (doublet : 680nm - 678nm), fine lines at 665 - 655 - 649 - 640nm, partial absorption between 620nm and 545nm. (the spectrum visible is the one of chrome)
- Fluorescence : none in most cases. Chrysoberyl green : weak dark red fluorescence.
For alexandrite : weak to inert for pale stones, slightly red or orangy-red for the dark stones under S.W.U.V. & L.W.U.V.
Occurrences :
- Sometimes associated to beryl, to aquamarine or to heliodor. It is an alluvial stone of granitic pegmatites.  This stone is sometimes found in the gem-bearing gravels of Sri Lanka and is also encountered in Brazil, Madagascar, Russia and the U.S.A..
- Alexandrites : Ural, Sri Lanka, Brazil, Myanmar, Zimbabwe.
- Others : Brazil, Sri Lanka, Zimbabwe, Madagascar, Myanmar, U.S.A..
Inclusions :
Inclusions are rare but when present, they are cavities of the crystal with two phases and assembled in healing fractures (liquid).
It is also possible to see traces of growth interruptions of the crystal or surfaces of healing (fingerprints) between growth planes.
Confusions :
Sapphire green-yellow, Andalousite, Brazilianite, Peridot, Zircon, demantoid Garnet, green-yellow grossular Garnet, Spodumene, Topaz, yellow Tourmaline, Beryl, Quartz, Orthose.
Imitations :
Glass and green-yellow synthetic sapphires, synthetic spinel, doublets (garnet - green glass).
Synthetics : .
See synthetics.

See also :
- Chrysoberyl – Katzenauge - Alexandrite, by K. Schlossmacher (ZDG n°40 , 1962, page 9).
- Imitation Katzenauge und Glass (ZDG n°43, 1963, page 33).
- Diagnostics of chrysoberyl - alexandrite with high indices (ZDG n°61, 1967, page 54).
- Modern Synthetic Gemstones by R. Webster (TJG Vol.12 n°4, 1970, page 115).
- Imitation einer grüner Katzenauge (ZDG n°43, 1963, page 33).

See also the Gemmological News concerning the chrysoberyls.

CHRYSOBERYLLUS :
Prohibited appellation for a greenish yellow beryl.

CHRYSOCOLLA :
Or chrysocolle, chrysocale.

Etym. : from the Greek ‘khrusos’ meaning ‘gold’ (for its colour) and ‘kolla’ meaning ‘glue’ (because in Antiquity it was used to solder gold ; note : it is also possible that this name designated borax, which the Greek obtained from the salt lakes of Persia or India; etym. : from the Hebrew ‘borak’ meaning ‘white’)
Hydrated silicate of copper.
(Cu,Al) ₂H₂Si₂O₅ (OH) ₄.nH₂O
Microcrystalline stone.
Physical and optical properties:
- Colours : green, blue turquoise, blue-green, sky blue.

- Transparent : Opaque , sometimes slightly translucent

- Lustre : vitreous, waxy, earthy
- Hardness : 2 to 4
- S.G. : 2.00 to 2.45
- R.I. : 1.46 to 1.57
- Crystal system : amorphous.
Chrysocolla takes part in the association of minerals forming Eilat stone (chrysocolla, turquoise, malachite and other copper minerals).
Occurrences :
USA, Dem. Rep. of Congo, Chile, Russia.
Confusions :
- Turquoise (S.G. : 2.6 to 2.9 ; R.I. : 1.6 ; opaque).
- "Eilat stone " (mixture of chrysocolla, turquoise and malachite S.G. : 2.8 to 3.2).
- Chalcedony blue (S.G. : 2.65 ; R.I. : 1.54 ; microcrystalline).
Remarques :
Name given in Antiquity to designate a mineral used when soldering gold (probably borax).

CHRYSOLITE :
Formerly called Chrysolithe and nowadays synonym of Peridot.
Meaning " Golden stone", this appellation has been used for many different stones but it is now only accepted for very light coloured Peridots. Formerly (Antiquity), this term was also at one time used to designate topaz.
Prohibited appellations :
- " oriental Chrysolite " Prohibited appellation for a sapphire.
- " oriental Chrysolite ", " Chrysolite from the Orient ", " Chrysolite from Brazil ", Prohibited appellations for Chrysoberyl.
- " aquamarine Chrysolite " Prohibited appellation for Beryl.
- " Chrysolite from the Urals " Prohibited appellation for green Uvarovite Garnet.
- " Chrysolite " Prohibited appellation for natural glass, Obsidian or Moldavite.
- " Chrysolite from Siberia " Prohibited appellation for green Demantoid Garnet.
- " Chrysolite from Ceylon " Prohibited appellation for green to yellowish-green Tourmaline or, to other authors, for a chrysoberyl.
- " Chrysolite from the Cape " Prohibited appellation for a variety of Prehnite.
- " Chrysolite " Prohibited appellation for Jade or Emerald.
- " Chrysolite " Prohibited appellation for greenish-yellow beryl.
- " Chrysolite from Brazil " Prohibited appellation for chrysoberyl.
- " Chrysolite from Bohemia " Prohibited appellation for moldavite.
- " Chrysolite d'eau " French. Prohibited appellation for moldavite.
- " Chrysolite from Saxony " Prohibited appellation for a variety of topaz.

(CHRYSOLITE) TOPAZ :

Prohibited Appellation for a pale yellow or yellowish green topaz .

CHRYSOPAL :
(for some authors) Synonym for cymophane.
(for some authors) Common translucent Opal from Silesia of apple-green colour.
(for some authors) Opalescent peridot.

CHRYSOPARE :
Synonym for gem topaz or chrysolite of Antiquity.

CHRYSOPRASE :
Belongs to the microcrystalline Quartz Group.
Variety of Chalcedony , green and containing nickel.
The most precious variety of the group of the chalcedonies. This microcrystalline stone is relatively rare and mainly cut as cabochon.

Silicon dioxide.

SiO₂
Physical and optical properties:
- Colours : light green, apple-green, vivid green. The colour is due to fine particles of hydrosilicates of nickel dispersed in the mass.

- Transparency : translucent to opaque
- Hardness : 6.5 to 7
- S.G. : 2.58 to 2.64.
- R.I. : 1.530 - 1.539 (+0.004 sometimes visible).
- Cleavage none.
- Crystal system : trigonal (microcrystalline aggregates).
- Spectrum : fine absorption line at 444 for the natural stones very difficult to observe;

                    fine absorption lines at 444 and 632 for the stones treated with nickel salts.
Occurrences :
Brazil, Australia, U.S.A. (California), Ural, Germany, Egypt, India, China, Japan, Colombia, England, Uruguay, New Caledonia.
Imitations :
Agates and chalcedonies tinted with chromium salts and green glass.
Confusions :
- Agate dyed green (S.G. : 2.65 ; R.I. : ± 1.54 ; superficially translucent ; chromium spectrum).
- All green rocks and minerals (ex. jades) and all green translucent gems (ex. emerald).
Erroneous Appellation :
The term blue Chrysoprase has been erroneously given to a Chalcedony containing inclusions of Chrysocolla.
See also :
- Chrysoprase aus Brasil (ZDG n°41 , 1962, page 22).
- Chrysoprase aus Australien (ZDG n°49, 1964, page 35).
- Imitation von Chrysoprase aus Australien (ZDG n°50 , 1964, page 31).
- Neue Provenienz von Chrysoprase in Australien (Queensland) (ZDG n°51, 1965, page 49).
- Neue Entdeckung von grüner Chalcedon (ZDG n°60, 1967, page 36).
Remark :
The term designated formerly (Antiquity / Middle Ages) noble Topaz.

CHRYSOQUARTZ :
Synonym for green aventurine quartz.

CHRYSOTILE :
A very fine fibrous variety of Serpentine , (hydrated silicate of magnesium), popularly known as asbestos.
Among the varieties of Chrysotile there is among others Satelite, one of the commercialised types of asbestos.

In gemmology important as typical inclusion (form of a horse-tail) in demantoid garnet from the Urals.

2[Mg₃Si₂O₅(OH)₄]

CH'UTI :
Chinese name designating a Jade tinted by oxides.

CHUSITE :
Alteration of Peridot.