Written by Alain Darbellay GGGems

2004 All rights reserved.

Gemology is by definitionrepparttar study orrepparttar 109303 science ofrepparttar 109304 precious stones. One knows approximately 4000 minerals produced byrepparttar 109305 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 onrepparttar 109306 following characters: Transparent minerals: The glare (brightness) dispersion (fire)repparttar 109307 transparency (purity) intensity of repparttar 109308 color (forrepparttar 109309 colored stones) Translucent minerals : Color orrepparttar 109310 reflection, opalescence,repparttar 109311 changing luster or asterism (inrepparttar 109312 case ofrepparttar 109313 phenomenal stones) Opaque minerals: Purity and intensity ofrepparttar 109314 color,repparttar 109315 propensity with reflecting their color well and takingrepparttar 109316 polish. All these factors of beauty are highlighted byrepparttar 109317 size and polishing. Durability depends on resistance torepparttar 109318 mechanical or chemical attacks to whichrepparttar 109319 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 isrepparttar 109320 study ofrepparttar 109321 significant properties ofrepparttar 109322 gems it serves ofrepparttar 109323 apparatuses or instruments necessary torepparttar 109324 observation andrepparttar 109325 measurement of these properties.

The gemologist must be able to differentiaterepparttar 109326 natural stones fromrepparttar 109327 synthetic stones using his instruments. - Here arerepparttar 109328 principal instruments used byrepparttar 109329 gemologist: The eye which will transmit torepparttar 109330 brainrepparttar 109331 visual data processed instantaneously byrepparttar 109332 data base in it containingrepparttar 109333 more or less large experiment ofrepparttar 109334 gem's observer. The loupe"10x" It is under this enlarging that, by International Convention,repparttar 109335 purity ofrepparttar 109336 stones must be given. Especially diamond. The strong curve ofrepparttar 109337 lenses used forrepparttar 109338 loupe "10x" has as a corollary a considerable marginal distortion and chromatic aberrations, unlessrepparttar 109339 loupe is made up of a whole of lenses calculated to eliminate these disadvantages. An anastigmatic loupe of good quality is significant forrepparttar 109340 gemologist. The preliminary examination atrepparttar 109341 eye then withrepparttar 109342 loupe "10x" is thus of primary importance becauserepparttar 109343 characteristic signs of a gem will helprepparttar 109344 gemologist to choose effective instruments forrepparttar 109345 identification.

- The characteristic signs of a gem which one can observe atrepparttar 109346 naked eye or withrepparttar 109347 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 betweenrepparttar 109348 facets: sharp or round, often withrepparttar 109349 concave facets (indication of glass or a cast plastic) or notched (stone of low hardness).

Abundant inclusions: which makerepparttar 109350 gems translucent, and by consequence,repparttar 109351 optical signs could not be obtained underrepparttar 109352 polariscope. Moreover, one could not insist enough onrepparttar 109353 importance of a perfect cleanliness ofrepparttar 109354 stones to examine. The cleaning ofrepparttar 109355 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 dirtyingrepparttar 109356 stones,repparttar 109357 specialized tweezers represent a pleasant complement ofrepparttar 109358 fingers. - Scale determiningrepparttar 109359 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 atrepparttar 109360 naked eye; this is why you can usually see these inclusions onrepparttar 109361 screen. The Polariscope, here a pocket polariscope. It isrepparttar 109362 usual means by which one differentiates onrepparttar 109363 one hand repparttar 109364 unirefractives substances (amorphous or coming fromrepparttar 109365 cubic system) andrepparttar 109366 birefractives substances, coming fromrepparttar 109367 other systems of crystallization. This instrument is composed of two filters polarizing between which repparttar 109368 stone is placed, and it is while turningrepparttar 109369 filter ofrepparttar 109370 top that repparttar 109371 analysis can be done. The refractometer is used to determinerepparttar 109372 indexes of refraction of repparttar 109373 stone. This instrument calculates speed with which luminous rays arise fromrepparttar 109374 stone and indicates it on a scale. The gem is placed on a coated pane of a fine particle of liquid made up amongst

Ilakaka Madagascar ( Sapphire rush )

Written by Alain Darbellay GGGems

2004 All rights reserved. ILAKAKA The plateau of Ilakaka in 1992. Ilakaka is located onrepparttar road to Tulear, south-west of Madagascar. The discovery of sapphire inrepparttar 109302 current of 1998 transformedrepparttar 109303 area. Ilakaka in 1999. It is inrepparttar 109304 accesses ofrepparttar 109305 downwards brook named Ilakaka thatrepparttar 109306 first sapphires were found in 1998. The existence of gemmiferous minerals, including corundum was known for a long time inrepparttar 109307 sandstones of Isalo. French geologists having undertaken research in 1946 in particular. If their discovery did not cause particular interest atrepparttar 109308 time, several reasons can be advanced : repparttar 109309 political instability which reigned afterrepparttar 109310 second world war inrepparttar 109311 colony, andrepparttar 109312 fact thatrepparttar 109313 majority of corundums coming fromrepparttar 109314 area of Ilakaka must be heated to be marketed, indeed, a blue stone, but cloudy, could not inevitably let suppose to its discoverers that it would become pure and transparent after a suitable heat treatment. Moreover, knowledge in this field remained summary at that time. In Ilakaka,repparttar 109315 arrival of merchants coming from Thailand and from Sri-Lanka changed things, because this group of purchasers became experts in "the " Tsy misy mandronono, tsy misy prix" enhancement of corundum." Thus,repparttar 109316 cloudy stones of This sentence is none by everyone in better quality will be often sold as (untreated Sri-Lankan Ilakaka. sapphires) onrepparttar 109317 international market, this because of It means that : " ifrepparttar 109318 stone is not milky,repparttar 109319 difficulties in detecting heating treatment in a stone its owner will not get price for it." from Ilakaka not containing other inclusion only one haze of fine titanium drops, reabsorbed after heating. ( Note: that true untreated Sri-Lankan sapphires are rare.) The excavations followrepparttar 109320 gravel deposits whichrepparttar 109321 Impressing holes borerepparttar 109322 sandstones of Madagascans call lalam' bato, (the way of stones.) Ilakaka testifying torepparttar 109323 fever of sapphire. Ankaboka, one ofrepparttar 109324 many gemmiferous places ofrepparttar 109325 area. Maromiandry is located The sivany (sifting of gravels) in Maromiandry. 40 kilometers north ofrepparttar 109326 Seldom practiced dry as in this place distant trunk road between from a river. Ilakaka and Sakaraha. The sifting of gemmiferous gravels in river close to Maromiandry.

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