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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).
Abundant inclusions: which make gems translucent, and by consequence, optical signs could not be obtained under polariscope. Moreover, one could not insist enough on importance of a perfect cleanliness of stones to examine. The cleaning of unset stones is easy; it is enough to wipe them with a clean handkerchief. A good cleaning can be obtained with water accompanied by a little liquid detergent. To avoid dirtying stones, specialized tweezers represent a pleasant complement of fingers. - Scale determining purity of a stone. - FL NFL LI1 LI2 MI1 Flaw less Near flaw less Lightly included 1 Lightly included 2 Medium included 1 -------------------------------------------------- MI2 MI3 VI1 VI2 HI Medium included 2 Medium included 3 Very included 1 Very included 2 Highly included Note that our camera can grasp very small inclusions almost invisible at naked eye; this is why you can usually see these inclusions on screen. The Polariscope, here a pocket polariscope. It is usual means by which one differentiates on one hand unirefractives substances (amorphous or coming from cubic system) and birefractives substances, coming from other systems of crystallization. This instrument is composed of two filters polarizing between which stone is placed, and it is while turning filter of top that analysis can be done. The refractometer is used to determine indexes of refraction of stone. This instrument calculates speed with which luminous rays arise from stone and indicates it on a scale. The gem is placed on a coated pane of a fine particle of liquid made up amongst