Cabochon:
It is a type of gemstone cut where the upper part is a rounded convex surface (dome-shaped).
This type of cut is also used to emphasize certain effects such as asterism and chatoyancy.
Chaceldony:
From "Khalkedon", a city near Istanbul.
Refractive index: 1.564/1.660.
Hardness: 7
Crystal system: microcrystalline
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Calcite: カルサイト Ca CO3 
From latin "calx" = chalk.
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Campo del Cielo:
Ferrous Meteorite. It’s name comes from the locality where it was discovered.
Localization: Campo del Cielo, Gran Chaco Gualamba, Argentina, approximately 900 km of north-north-west of Buenos Aires. Latitude 27 degrees 39 minutes south, longitude 61 degrees 44 minutes.
Structual class: Octaedrite , Og, band width 3,0 ±0.6 Widmanstatten.
Chemical class: Group I, 6,68% Ni, 0,43% Co, 0,25% P, 87 pages per minute Ga, 407 GES pages per minute.
Estimated fall date: between 4,000 to 6,000 years ago
History: This meteorite was first discovered in 1576. A Spanish governor received blocks of iron from Indians who were convinced that they had fallen from the sky. The governor sent out an expedition under the command of Captain Miraval that brought back a few pieces of an enormous mass of iron that he called Meson de Fierro (large iron table).
The place of this discovery was Campo del Cielo (Field of Heaven), a name very well suited for a meteorite fall! This area is a dry open plain with no other large rocks. These are ideal conditions to allow these meteorites to be found.
It wasn’t until 1770 that this meteorite was “rediscovered”. The Spanish believed that the material might contain silver. After treatment it became obvious that it contained only iron.
A Spanish Navy Lieutenant extracted a specimen that he claimed weighed between 14 and 18 tons. It was baptized " Meson de Fierro ". This meteorite was left in place... and has never been found again.
In the 19th century, small meteorites were found in this same area. But it wasn’t until the 20th century that systematic explorations showed important iron masses, while still not finding the " Meson de Fierro ".
In 1992, the American meteorite collector and merchant, Robert Haag was arrested by Argentinian authorities while transporting a meteorite of 37 tons from the area. Haag had bought the mass from an Argentinian who had claimed ownership. Haag was released and this enormous meteorite remained in Argentina.
Craters: The largest meteorites from Campo del Cielo were found in and around a series of small craters in the south-west part of the of the principal field. The largest crater is 78 by 65 meters. Another smaller crater is 56 meters in diameter and 5 meters deep. A dozen craters were noted.
The principal masses were found in these craters. Scientists dated the carbonized wood found in these craters. Dates of 5800 years ago (+/-200 years) and 3950 years ago (+/- 90 years) were obtained. These dates conform with the Indian oral tradition that "iron fell from the sky."
Several of the meteorites of Campo are very rusted and corroded by earthly chlorides, however some have zones showing a crust of relatively fresh fusion. This is also an indication of strikes in the not too distant past.
Structure:
Campo del Cielo is described as a polycrystalline octaedrite at 3 millimeter Widmanstatten bands.
The mass is composed of large crystals of Austenite of 5 to 50 centimetres. The structural study of this meteorite allows one to think that the original body was tabular in form and broke up upon it’s entry into the atmosphere.
Chemical: Campo del Cielo is classified in the group I, 6,68% Ni, 0,43% Co, 0,25% P, 87 p per minute Ga, 407 GES pages per minute, 3.6 p per minute Ires . The rest of it’s composition is exclusively iron.
The important minerals are:
Kamacite: this iron and nickel alloy is that of about 90% of the crystals of centimetric dimension. The Neumann bands are common (communal).
Taenite and Plessite are the other constituants of the iron-nickel alloy. It is found in grains.
Schreibersite is present in minute quantities.
Troilite is present in the graphite and silicate aggregats.
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Carrolite: キャロライト Cu (Co,Ni)2 S4 
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Carat:
The carat is a unit of weight used for the gems. This word comes from the Greek word "keration" (little horn), which then made it’s way into Italian (carato) and then into Arabic (qîrât, small weight). This small weight was based on the small seed from the Carob tree which was used as a measure of weight due to it’s uniform size. In 1907, the (metric) carat was defined as being equal to 200 milligrams (0.2g)
The carat also indicates the proportion of gold in an alloy. An alloy with 50% gold is called 12 carat; pure gold is 24 carat. The caratage most used in France is 18 carat (or 750/000) that is to say 18 parts of pure gold and 6 parts of other metals.
Cassiterite: キャシテライト Sn O2 
From the Greek "kassiteros" = tin. Tin oxide.
Celestite: 天青石 Sr SO4
From the latin "coelestis" = celeste.
Cerusite: Pb CO3. 
_ From the latin "cerussa" which designated a white paint.
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Chart:
Many gem identification charts exist. They permit gem identification by classification tables according to certain criteria: color, refractive index, birefringence, crystalline system, density, hardness.
Created by Herve Nicolas, gemologist, faceter (and world traveler), the "Blue Chart" is, in our opinion, the best one currently available. It is only available in English.
Available on gemfrance
Charoïte: K (Ca,Na)2 Si4 O10 (OH,F) H2 O (?)
Author: Rogova in 1978.
Etymology: from is locality of discovey the Charo River, montain of Murun, Aldan, Yakoutie, Russia.
_ See gallery
Chrysoberyl: クリソベリル Beryllium aluminium oxide.
Al2. 
When the aluminium and the beryllium are replaced by iron, the gemstone has a green-yellow, yellow-brown, olive green, grey-green or colorless to brownish color and is called chrysoberyl.
When the aluminium is replace by chromium, the gem is called Alexandrite and changes color depending on the light source: green in daylight, violet to red under incandescent light.
The rarest variety of chrysoberyl is Alexandrite.
Cat’s Eye Chrysoberyl has inclusions in tiny parallel channels that produce a luminous silvery white band which appears to slide on the stone’s surface.
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Chrysoprase: 
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Citrine: シトリン SiO2. 
_ From the latin "citrus" = lemon, because of it’s yellow to yellow-brown color.
It’s a variety of quartz. The color, yellow for citrine and purple for amethyst depends on the temperature at which it crystalized.
Many citrines on the market are heated amethysts. The deepest color is known as "Madeira Citrine". For these gems, the name "Madeira topaz" was used. This denomination is now prohibited. It created confusion (sometimes deliberate confusion...) with Topaz, gems of higher commercial value. Thus, many Madeira Citrine owners believe they have a topaz.
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Clinochlorite:(Mg,Fe+2)5 Al (Si3 Al) O10 (OH)8
Etymolgy: from the greek "klino" = to lean and "khloros" = green, because of it’s color and it’s optical axis.
Belongs to the chlorite group.
Discovered by Blake in 1851.
Clinozoisite:
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Cordierite: (Mg,Fe)2 Al4 Si5 O18 x(H2 O,CO2)
It owes it’s name to the French mineralogist P.L.A. Cordier. It’s also called Iolite because of it’s purple color, and also called Dichroite because of it’s strong dichroism. The blue color is due to iron. Depending on the angle at which it is looked at, the color of the stone can pass from blue-violet to the gray-yellow.
Color:
The color of gemstones is primarily due to metals and their chemical bonds, that exist in the composition of a gem. Chromium, iron, cobalt, copper, manganese, nickel, titanium, vanadium absorb precise wavelengths of light and thus contribute to the color that we see.
Diamonds exist in all colors.
All white to tinted yellow diamonds are classified according to a precise color scale, D with Z, which is used internationally.
GIA = FORMER DENOMINATION
D E = River
F G = Top Weslton
H = Wesselton
I J = Top Crystal
K L = Crystal
M N = Top cape
O P = Cape
Q R = Light yellow
S... Z = Yellow
Crocoite: 紅鉛鉱 PbCrO4 
Etymology: an allusion to it’s color, it’s name comes from the Greek:"Krokos" = saffron.
Discovered by Beudan in 1832.
A rare mineral, especially in gem quality. The mine providing the most beautiful pieces is in Tasmania.
It’s a secondary oxidation mineral that forms in lead veins that are infiltrated by chromium charged fluids.
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Cuprite: キュープライト Cu2 +1 O 
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Cyanite: 
Synonym of Kyanite and Disthene.
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