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Gemology classification of precious, semi precious and ornamental gemstones

Gemology classification of precious, semi precious and ornamental gemstones
Gemstones classification by groups
Precious and semi precious gemstones
Ornamental gemstones
Gemstones classification by value
Deposits of gemstones
Application of gemstones

This is the diverse on mineralogical structure group of minerals which shares on actually precious, semi-precious and ornamental gemstones.

Precious and semi precious gemstones

Demantoid gemstone

Minerals concern to jewels (mainly crystals), colorless or having beautiful colouring, bright shine, the greater or smaller transparency, high hardness (from 5 up to 10 on a mineralogical scale), stability to wearability, high dispersion, cleanliness of tone of colouring, uniformity of color. All of them go mainly for a facet.

Shine of jewels is defined to inherent these minerals by optical property - high factor of refraction. Shine and game of the reflected beams amplify by special facet. Appreciated optical properties are effects of opalescence and irisation, giving bright game of colours (for example, opal), asterism (light game of reflected beams as a 6-beam star, for example astrosapphire), change of color at various illumination (for example, alexandrite), polychroism (distinction in colouring at passage of light on different directions in a crystal).

Hardness defines stability to wear process, ability to keep polishing, sharp corners and edges of a facet.

Value of jewels is defined by their rarity - an expense of a plenty of work for searches and extraction, high cost of a facet, and also individual qualities of stones - size, uniformity, beauty of color etc. The quotation in view of specific features of a stone is made on carats (1 carat = 200 mg); for pearls for unit of the quotation it is accepted gran = 0,25 carats.

Ornamental gemstones

Jasper gemstone

Ornamental gemstones are semi-transparent, frequently opaque mineral units, rocks and other minerals with color inclusions or the figure. Ornamental gemstones used for large art - decorative hand-made articles (a table-top, a vase, wall panels, Florence mosaic and other), for fine inserts, an ornament, and also for the technical purposes (for example, a jasper, a nephrite, malachite, agate, fluorite etc.).

On physicomechanical properties ornamental gemstones share on firm (5 and higher on a mineralogical scale, for example a nephrite, a jasper, agate etc.) and soft (4 and low, for example malachite, marble onyx, fluorite etc.).

Value of ornamental gemstones is defined also by a rarity of a presence, individual properties (beauty of color, figures), and also the work spent on their processing. The quotation of raw material in view of individual properties of a stone is made on kgs, centners.

Classification by value

Gemstone

According to A.E.Fersman and M.Bauer's classification of these two main groups precious and ornamental gemstones are subdivided into classes (I, II, III) depending on relative value of gemstones united in them.

Jewels (precious and semi precious gemstones) of the I class: diamond, sapphire, a ruby, an emerald, alexandrite, hrizoberill, noble shpinel, evklaz. Pearls - also a jewel of this group is an organic origin. Valuable gemstones are jewels with much pure, transparent, equal rich tone. Badly colored, muddy, with cracks and with other lacks gemstones of this class can be appreciated below jewels of the II class.

Jewels of the II class: The topaz, beryl (aquamarine, vorobievit, geliodor), pink tourmaline (rubellite), fenakit, demantoid (the Ural chrysolite), amethyst, almandin, pirop, uvarovit, hromdiopsid, zircon (a hyacinth, yellow and green zircon), noble opal. At exclusive beauty of tone, a transparency and size the listed gemstones sometimes are appreciated alongside with jewels of the I class.

Jewels of the III class: turquoise, green and polychrome tourmalines, kordierit, spodumen (kuntsit), dioptaz, epidot, rock crystal, smoky quartz (rauhtopaz), light amethyst, a cornelian, a heliotrope, chrysoprase, semi-opal, agate, field shpats (a solar stone, a moonstone), sodalite, prenit, andaluzit, diopsid, hematite (blooded), pirit, rutile, amber, gagate. Only rare kinds and items have high cost. Many of them by application and values are so-called semi precious gemstones.

Ornamental gemstones of the I class: nephrite, jade, lazurite, sodalite, glavkolite, amazonite, labrador, rhodonite, malachite, aventurin, quartzite, smoky and pink quartz, chalcedons (perelift, prazem), agate, jaspers, vezuvian (californit), a written granite (pegmatit).

Ornamental gemstones of the II class: serpentine, agal'matolit, steatit, selenite, anhydrite, obsidian, marble onyx (east onyx), fluorite, stone salt.

Ornamental gemstones of the III class: plaster, alabaster, a marble, porphyries, breccias, quartzite etc. They already concern more to so-called ornamental materials (decorative stones), used in architectural-art business.

For giving brighter color precious, semi precious and ornamental gemstones paint various chemical dyes (for example, red, black and dark blue agate, a cornelian etc.). Color of some jewels before a facet can change in a desirable direction by heating or influence on a mineral the radioactive radiation x-ray and ultra-violet beams (for example, at an radium irradiation colorless diamond becomes green).

Artificial and synthetic jewels represent special group of jewels. Among synthetic jewels diamond, an emerald, corundum (sapphire, a ruby), shpinel, colorless rutile (diamond simulating on shine) are known. Coloring synthetic corundum and shpinel by introduction of impurity (Cr, Ti, V, Fe etc.), on their basis receive "amethyst", "alexandrite", "aquamarines" and others. In the synthetic way receive for a facet also all versions of crystal quartz (rock crystal, amethyst etc.). There are numerous imitations of jewels. It is necessary to distinguish imitations (artificial) and synthetic stones identical or close to natural jewels. Imitations are made from a srtass, a glass, the slag, painted by various impurity, and plastic (it is especial for imitation of amber).

Deposits of gemstones

Stone deposits

Deposits of precious, semi precious and ornamental gemstones are connected to very wide complex of natural processes. Formation of radical deposits precious, semi precious and ornamental gemstones is caused by the following processes: a) crystallization from the basic deep magmas, rich magnesium and iron (diamond, pirop etc.); b) crystallization in granite pegmatits various genetic types (beryl, an emerald, aquamarine, zircon, a topaz, tourmaline, amazonite etc.); c) crystallization from hot and cold mineralized water solutions of a deep or superficial origin (opals, rock crystal, amethyst, turquoise, agate, malachite etc.); d) formation in metamorphical and contactal-metasomatical deposits (a ruby, sapphire, shpinel, lazurite, granates, jadeite etc.). Frequently places of extraction of jewels are connected to the looses arising at destruction of radical breeds in which these minerals were generated. Some precious, semi precious and ornamental gemstones have organic origin (pearls, amber).

Deposits of precious, semi precious and ornamental gemstones of various genetic types are widely distributed all over the world. Russia has a lot of deposits precious, semi precious and ornamental gemstones. Remarkable deposits of color jaspers on Ural and Altay are given the best in the world on beauty of a stone and size of blocks materials for large works of art. Green malachite and red rhodonite with beautiful black figure from deposits of Ural, a nephrite from East Sajan, dark blue lazurite from Baikal are the best in the world on beauty and technical advantages gemstones. The huge number of the diverse on figure and a coloring marbles is opened and is extracted in deposits of Ukraine, Ural, in Karelia, on Caucasus and in Transcaucasus, in Central Asia, in East and Western Siberia. Marble onyx of beautiful figure and colouring is present in deposits of Armenia and Uzbekistan, a deposit of agate and chalcedonies in Transcaucasus, Eastern Siberia. "The Siberian aquamarines" of blue, colors of sea water from deposits of Ural and Eastern Siberia, the Ural emerald, different shades topazes and amethyst of Ural are not less known and considered as the best on color and quality gemstones. The largest in the world deposits of amber are in the Kaliningrad area. Deposits of turquoise in Central Asia, diamonds in the Ural and Yakut, fiery opal in Kazakhstan, numerous deposits of rock crystal on Ural, in Kazakhstan, on Pamir, in Eastern Siberia are opened.

Are appreciated also: The Ural alexandrite - green in the afternoon and vine-red at artificial illumination; bright-pink "sibirite" - tourmaline of the Ural and Siberian deposits; fenakits - similarly to diamonds; an emerald-green granate - demantoid.

Deposits of precious, semi precious and ornamental gemstones are known in Africa, South America, Asia, Europe and Australia. Extraction of them is located rather non-uniformly. Value of diamonds of Southern Africa is about 90 % of all extracted precious, semi precious and ornamental gemstones; the greatest amount and a variety of a precious and semi precious gemstone (without diamonds of Southern Africa) extract in Asia, the second is a South America, Africa (including Madagascar), Europe and Australia. In Africa and on island Madagascar extract diamond, an emerald, beryl, aquamarine, tourmaline, rock crystal, a topaz, pirop etc. South America (mainly Brazil and Columbia) is the large supplier of an emerald, beryl, aquamarine, a pink topaz, amethyst, agate, fenakit, diamond, tourmaline etc. In the countries of Asia there are remarkable deposits of a nephrite (China), turquoise, lazurite (Iran, Afghanistan), diamond, sapphire, a ruby, shpinel, zircon, jadeite, almandin etc. (India, Sri Lanka, Thailand). In some countries of Europe extract a red granate - pirop (Czech), a marble, breccias and other ornamental gemstones (Greece, Sweden, Italy), fluorite (Great Britain), noble opal (Hungary and Czech). In Australia opals are extracted. Northern America is rather poor jewels (pink beryl, poli-chrom tourmaline and low-grade turquoise).

Application of gemstones

Malachite tower lid box

Application of precious, semi precious and ornamental gemstones in connection with development of exact instrument making and special industries (the electronic-industry etc.) has strongly changed. The engineering of manufacturing of a synthetic gemstone (a ruby, sapphire, shpinel) and every possible cheap fakes and imitations was developed. The most part of jewels used for the technical purposes where consumption of them all grows. Due to the big hardness diamond is widely applied in engineering of a chisel affair, for cutting and polishing of firm materials etc. The ruby and sapphires, mainly synthetic, are used in clock business and for base in exact mechanisms. Transparent quartz, tourmaline are widely applied to special optical devices, and also in the electronic-industry. Agate, chalcedony and their versions in large quantities used in manufacturing of details of exact weights and measuring tools, and also chemistry etc.

Precious, semi precious and ornamental gemstones from most ancient times were used alongside with bowls, a bone, a horn, a tree for a beads, bracelets, amulets. Precious, semi precious and ornamental stones have found also wide application in art, for decorating furniture, facing of vase and jewelry boxes (mainly malachite), manufacturing of shanks of knifes and spoons. Precious, semi precious and ornamental gemstones frequently has an independent art value, in jewelry as their basic part according their jewelry qualities.

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