Gemstone Classification

Chemical Composition

• pure chemical element such as carbon (etc. diamond)
• Compound such as silicon dioxide (SiO2) - quartz
• mixture of compound such as calcium silicates, iron, magnesium, etc
• silicates
• oxides

Crystal Structure
Gemstones may be formed in single or multiple discrete crystals
massive collections of microscopic crystals (cryptocrystalline ) (such as chalcedony)
amorphous (non-crystalline)

Crystal system

• Cubic-Gemstones occurring in cubic crystal forms include diamond, the garnets, pyrite, and spinel
• Hexagonal-Gemstones occurring in hexagonal crystals include beryl, corundum, quartz, and tourmaline
• Tetragonal-include zircon, rutile, and scapolite.
• Orthorhombic-topaz
• Monoclinic-Jadeite and nephrite

• Triclinic-labradorite

Optical

• color-color that crystal obsorb and permits to emit
• Optic Character-crystal structure that will effect the light passage
• Refractive index (R.I)-Ratio of velocity of light passing throught air to the velocity of light passing throught transparent body of crystal. The higher the more brilliant. Diamond has 2.4 and typical quartz 1.54 -155 R.I
• Dispersion-when crystal separate lighti into spectrum of color
• Clarity-Gemstone usually has foriegn microscopic or inclusions of other crystal.

Specific Gravity

the ratio of the density of a gemstone relative to that of water
Durability
Sometimes a combination of Hardness and thougness of crystal. Hardness unit Mohs familiar to a diamond

Gemstone

  

  
What?

• A precious / semi-precious stone which is earth minerals
• but certain are synthetic or a fossil or just a beautiful rock
• they are cut and polish into desired shapes to make a jewelry
• they have their own beauty, hardness and index of refraction that make them shine
• Rarity is another characteristic that lends value to a gemstone
• precious gemstone - diamond, emerald, sapphire and ruby while other considerate as semi-precious
• classified by the chemical compositions and crystalline structure and crystal habit





Classification

• Gemstones are classified into different groups, species, and varieties
• Gems are characterized in terms of refractive index, dispersion, specific gravity, hardness, cleavage, fracture, and luster. They may exhibit pleochroism or double refraction. They may have luminescence and a distinctive absorption spectrum.
• Material or flaws within a stone may be present as inclusions. Some classified in term of 'water' respect to their clarity, transparency or luster. Example, very clear gems are 'first water' and so on 'second water' and 'third water'

Values




 

• No specific grading to crystal value
• but some using 'Four Cs' - Color, Cut, Clarity, and Carat to a diamond
• In crystal gems color also very influencing
• rare gemstone which mean unique one hard to find will add the gem value

Cutting & Polishing

• Some jewel is in their original form as they found
• most of jewel has been cut and and polished to enhanced the beauty and shinny
• Common cutting are cabochons and facets form

Treatments

• Heat - to improve color and clarity for example aquamarine when heat can change color from yellow to green or blue
• Radiation-change color such as quartz,topaz
• Waxing/Oiling-improve clarity and color
• Fracture filling-to make gemstone appear bigger

Synthetic and artificial gemstones

• Some gemstones are manufactured to imitate other gemstones example Moissanite
• However, lab created gemstones are not imitations such as diamond, ruby and sapphire. They can be created but with similar physical characteristics and chemical identity. 

Hybrid gemstone - contain artificial and natural components