Physical properties of Gemstones

Physical properties of Gemstones
The physical properties of gemstones, their hardness, their specific gravity or density and the way they break or “cleave”, depend on the chemical bonding and the atomic structure of the stone.
1. Hardness
2. Cleavage
3. Fracture
4. Specific Gravity
5. Crystallography
1.Hardness
Hardness of stone is measured by moh’s scale. It is best defined as a property possessed by a substance to resist abrasions when a pointed fragment of another substance is drawn across it.
2.Cleavage
Cleavage is the tendency of a crystallized mineral to break in certain definite directions, giving more or less a smooth surface.
3.Fracture
When a gemstone breaks along a surface that is not related to its internal atomic structure, it is said as a fracture. Fractured surfaces are generally uneven, and each has its own descriptive name.
4.Specific Gravity
Specific Gravity (SG) of a gem stone is an indication of its density. It is calculated by comparing the stone’s weight of equal volume of water. The greater the stone’s specific gravity, the higher it will feel.
5.Crystallography
Crystallography is a science of crystals. The properties by which gemstones are identified are entirely based upon its basic crystal structure. Rough crystals themselves are very beautiful and well formed crystal. It displays characteristics features such as cleavage surface, marking forms etc.

Instrument used for gem identification

Instrument used for gem identification

1. Microscope and 10z loupe
2. Refractor meter is used for finding refactrative index of the stone.
3. Dichroscope is used for finding out the properties of trichroism, diachronic and pleochroism.
4. Spectroscope is used or finding out the wave.
5. Ultra violet lamp is to detect the fluorescence and phosphorescence.
6. Choelsea filter is a dichromatic filter, which transmits Z wave’s lengths.

Moth’s scale

The hardness of stones is measured by the scale is called Mohs’ scale, named after Friedrich Mohe, a German mineralogist (1773- 1839.)If is based on the ability of one stone to be scratched by another, or to itself be scratched.

Scale

Category Family name
1. Talc
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Orthoclase
7. Quartz
8. Topaz
9. Corundum
10. Diamond

Gem Stones- Lusture & Dispersion

LUSTRE: The quality of light reflected off the surface of a stone .Use reflected light to judge.
- Metallic: Metal-like the highest possible luster .e.g. Hematite, Pyrite.
- Adamantine: The highest possible luster for gemstone .e.g. Diamond, Zircon, Dermatoid Garnet.
- Vitreous: Glass- like the most common luster for gemstone. E.g. Quartz, Beryl, Topaz.
- Greasy: An oily appearance; common for jade. Also seen in some garnets, peridot etc.
- Resinous: Similar to greasy; used to describe the luster of amber.
- Waxy: Little reflection; similar to the luster of a candle or a fingernail. E.g. Turquoise, Chalcedony.
- Dull: Very irregular, fine- grained surface; common on unpolished, opaque stones. E.g. rough Turquoise, Malachite.
- Silky: Reflection off fibrous structure (sheen), e.g. Tiger’s eye.
- Pearly:Due to structure (sheen); common to Pearl, rough moonstone, cleavage surfaces etc.

Dispersion: The breaking of white light into its component spectral colors.
- Observed as flashes of spectral colors, known as fire.
- A few stones have eye- visible dispersion which can be a useful identifying characteristic.
- The presence or absence of dispersion in diamond stimulants is important in their identification (e.g. strontium- titan ate – very high dispersion, YAG –barely visible dispersion).

Jewelry Designing - Parts of Gem Stone

Different Parts of stones-:
Crown
1.Table
2.Star facet
3.Bezel facet, crown main facet
4.Crown griddle facet
5.Griddle
Pavilion
1.Pavilion main facet
1.Culet
Entire form
1.Crown
2.Pavilion