Classification of gemstones.
Bauer reported, adopted for K.. E. Klugiem the division of stones, precious on 5 class. The basis of this division is primarily the hardness of the stones, having a major impact on their price. The right gemstones (jewelery), distinguished by high hardness (the highest among the minerals), with beautiful colors, transparency, strong shine and fire, and a rarity in the form of specimens suitable for grinding, have been divided into 3 class:
Grade I includes stones with a hardness of 8-10 on the 10-point Mohs hardness scale: 1) diament, 2) korund (rubin, sapphire), 3) chryzoberyl, 4) spinel.
Stones with a hardness of 7-8 were assigned to class II (except for the noble opal). Their value is generally lower than that of class I stones, but tall, and some varieties of stones of this, grades may cost more than grade I stones. They belong here: 5) zirconium, 6) beryl (emerald, akwamaryn i in.), 7) topaz, 8) tourmaline, 9) grenade, 10) noble opal.
Stones with a hardness of 6-7 and properties intermediate between precious and semi-precious stones belong to class III. They rarely have all the characteristics of a gemstone, however, they are much more common than the stones of the previous classes, but rare in the form of grindable specimens. They belong here: 11) cordierite, 12) wezuwian, 13) chrysolite (variety of olivine), 14) aksynit, 15) cyanite, 16) staurolit, 17) Andalusian, 18) chiastolit, 19) pistacyt (variation of the epidote), 20) turquoise.
Classes IV and V include the so-called. semiprecious stones, having only some or less of the properties of gemstones.
Stones of hardness belong to the class IV 4-7. Despite alive; color and gloss, only some of them are transparent, most often, however, only translucent. They are common stones, generally low price. They belong to this class: 21) different varieties of quartz, chalcedony and opal, 22) potassium feldspar (adulatur, amazonite), 23) labrador, 24) obsydian (volcanic glaze), 25) lazuryt (lapis lazuli), 26) hauyn, 27) hypersteps, 28) diopsyd, 29) fluoryt, 30) amber.
Class V includes opaque stones, low gloss, not pure in color, like a jet (compact variety of brown coal), nephrite, serpentyn, talk, cast (alabaster and fibrous gypsum), malachit, hematyt i in. Their value is low and largely depends on the type of processing.
Different detailed classification of stones, based mainly on their value and prices, was presented by the outstanding Soviet mineralogist and expert on precious stones A.. E. Fersman. Apart from the actual gemstones, he distinguished decorative stones as the second group. He divided each of these groups into 3 class.
He included precious stones in the 1st class: diament, noble varieties of corundum - sapphire and ruby, emerald (one of the varieties of beryllium), aleksandryt (a variety of chrysoberyl), spinel (noble) i euclaz. He also included pearls in this class, which although different, because it is of organic origin, are also classified as precious stones.
Fersman classified precious stones as class II: topaz, noble varieties of beryl (poza szmaragdem zaliczanym do klasy I, i.e.. akwamaryn i in.), zirconium, worobiewit, różową odmianę turmalinu (rubelit), fenakit, some grenades (demantoid, almandyn, pirop, uwarowit) and amethyst (dark varieties) and noble opal.
According to Fersman, gemstones belong to class III primarily: turquoise, tourmaline (outside the ruble), spodumen (kunzyt), dioptaz, epidote and varieties of quartz and chalcedony (smoky quartz, bright amethyst, chrysopraz, agat i in.). Fersman also included amber and jet in this class.
For decorative stones (decorative), having the characteristics of semi-precious stones, mainly opaque minerals are included, like jade and jade, lazuryt, some varieties of feldspar (amazonite, labrador), Rodon, malachite and some varieties of quartz and chalcedony. These minerals belong to the 1st class of this group of stones.
Do klasy II zaliczył Fersman serpentyn, agalmatolit, onyks, fluoryt i in.
W klasie III umieścił oprócz alabastru niektóre skały, jak marmury i porfiry, używane głównie jako architektoniczny materiał dekoracyjny.