Gemology is by definition study or science of precious stones. One knows approximately 4000 minerals produced by terrestrial body, among which less than 100 produce specimens considered as precious stones. So that a mineral is a gem, it must have three fundamental virtues. Beauty, durability and scarcity. Beauty; it depends on following characters: Transparent minerals: The glare (brightness) dispersion (fire) transparency (purity) intensity of color (for colored stones) Translucent minerals : Color or reflection, opalescence, changing luster or asterism (in case of phenomenal stones) Opaque minerals: Purity and intensity of color, propensity with reflecting their color well and taking polish. All these factors of beauty are highlighted by size and polishing. Durability depends on resistance to mechanical or chemical attacks to which stones are subjected. Dust often containing quartz particles. It is preferable that a gem is as hard as this mineral. Rarity: A gem often comes from a common and very widespread mineral species, but it consists of a specimen in which exist seldom joined together qualities.

Gemology is study of significant properties of gems it serves of apparatuses or instruments necessary to observation and measurement of these properties.

The gemologist must be able to differentiate natural stones from synthetic stones using his instruments. - Here are principal instruments used by gemologist: The eye which will transmit to brain visual data processed instantaneously by data base in it containing more or less large experiment of gem's observer. The loupe"10x" It is under this enlarging that, by International Convention, purity of stones must be given. Especially diamond. The strong curve of lenses used for loupe "10x" has as a corollary a considerable marginal distortion and chromatic aberrations, unless loupe is made up of a whole of lenses calculated to eliminate these disadvantages. An anastigmatic loupe of good quality is significant for gemologist. The preliminary examination at eye then with loupe "10x" is thus of primary importance because characteristic signs of a gem will help gemologist to choose effective instruments for identification.

- The characteristic signs of a gem which one can observe at naked eye or with loupe are as follows: Texture: rough gem or opaque

Gloss: diamantine, vitreous or resinous etc.

Substantial dispersion (indication of a high index of refraction) or weak, presence or absence of cleavages.

Characteristic fracture: vitreous, granulous or splintering etc.

Assembled stone: doublet or triplet.

Corners between facets: sharp or round, often with concave facets (indication of glass or a cast plastic) or notched (stone of low hardness).