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Gemstone

There are several thousand known minerals in nature (with estimates ranging from 2,000 to 7,000), but fewer than a hundred are considered gem minerals. Of these, only about a dozen or so are actually valuable enough to be important gemstones on the world market. In order to be considered a gemstone, a mineral must first of all be beautiful. In addition, it must be hard and durable. Its value increases if it is also rare. [Pg.151]

The beauty of a gem is measured in terms of its clarity, brilliance, and color. Its natural beauty can be enhanced by the way it is cut. There are two basic kinds of gem cuts faceted and cabochon. The faceted cut has many flat cut surfaces (facets) with an overall shape that might be round, oval, square, rectangular, or pear-shaped. Faceted cuts are preferred for brilliant transparent stones such as diamond. The cabochon cut has a smooth rounded top, usually with a flat base, and it is mainly used for opaque or translucent stones. [Pg.151]

Hardness is measured using the Mohs scale, on which 10 is hardest. (Diamond has a hardness of 10.) Gemstones should have a Mohs hardness of 6 or more. A really durable gem should have a hardness of at least 7, which is the hardness of quartz. Table 1 shows the hardness of some familiar minerals on the Mohs scale. [Pg.151]

Ruby is a variety of corundum (A1203) with a Mohs hardness of 9. Its red color results when chromic ions (Cr3+) replace some of the aluminum ions in the crystal. The finest rubies come from Myanmar (formerly Burma) or Kenya. Star rubies are stones with a special starlike appearance. They usually have a cabochon cut and appear to show a 6-pointed star due to microscopic inclusions. Rubies of very high quality are sometimes made synthetically. [Pg.151]

Sapphire, like ruby, is made of corundum (A1203) and has a hardness of 9. However, instead of Cr impurities, the crystal contains iron and titanium [Pg.151]

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) [Pg.212]

Gem is a general term used to describe precious and semi-precious stones, usually after they have been cut and polished. In archeology, it refers only to engraved stones (cameo, intaglio, seals, etc.). The term gem-quality is applied to rough material that is of a quality suitable for cutting or working [Pg.30]

The materials most commonly used as gems and ornamental stones are listed in Table 2.9. This is by no means a complete listing of all materials ever used in jewelry or for decorative purposes. There are many worked specimens that are one-of-a-kind, made from unexpected materials that were opportunistically obtained. These often pose problems of identification and consequently of conservation, since once a stone has been worked it loses its natural luster and form. Stones have been altered with dyes and heat for thousands of years, so it does not hold true that just because something is in an old artifact or Grandma s necklace that it cannot be dyed or otherwise not natural. Synthetics are relatively new, but imitations are as old as the stones themselves. If someone wanted a red gem, and there were no rubies available, then a garnet or spinel could be used instead. No emeralds Use an olivine (peridot) or green sapphire. A synthetic must have the same composition and internal structure as the natural material, but an imitation just has to look like the natural stone. [Pg.31]

Diamonds are the hardest natural substance, but they can cleave easily. They occur in every color, but shades of yellow and brown are most common. Today s faceted diamonds are cut and polished with tools embedded with tiny diamond chips or dust. Before the advent of modern methods, diamonds were used in their natural state, or roughly shaped and polished by hand. The hardness of this mineral led many early jewelers to do a minimum of work before setting diamonds in jewelry or regalia. Common imitations of diamond are colorless spinel, sapphire, zircon, topaz, quartz, and many synthetics. [Pg.31]

Rubies and sapphires are color varieties of the mineral corundum, which is simple aluminum oxide. This mineral is second only to diamond in hardness, but is much tougher and harder to break. Rubies are, by definition, red or purplish red. The term sapphire is used for every other color. [Pg.31]

Spinel is another simple oxide mineral. It is commonly seen today as a synthetic and may be any color. Natural red spinel was most prized as a gem, and usually was used as an imitation of ruby. Some notable pieces in the British and Russian crown jewels include large uncut spinels. These crystals are a deep red color and are distinctive because of their rough octahedral shape. [Pg.31]


It is produced artificially for use as a gemstone, but it is relatively soft. Star sapphires and rubies exhibit their asterism as a result of the presence of Ti02. [Pg.76]

Aquamarine [1327-51-1] [GEMSTONES - GEMSTONE MATERIALS] (Vol 12) [GEMSTONES - GEMSTONE TREATMENT] (Vol 12)... [Pg.67]


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Aluminum oxide in gemstones

Archaeological gemstones

Color of gemstones

Colors gemstones

Diamond as gemstones

Diamond gemstones

Emerald for Gemstones

GEMSTONE MATERIALS

Gemstone Chemistry

Gemstone coloration

Gemstone cutting

Gemstone treatment

Gemstones and Industrial Diamond

Gemstones artificial

Gemstones characteristics

Gemstones from melts

Gemstones from solutions

Gemstones impurities

Gemstones optical properties

Gemstones physical properties

Gemstones properties

Gemstones silicate

Gemstones stones

Gemstones synthetic

Gemstones technique

Gemstons ruby

Heat treatment, gemstones

Irradiation, gemstones

Mineral and Gemstone Properties Table

Minerals, Ores and Gemstones

Phosphate Minerals as Gemstones

Pigments, Minerals and Gemstones

Polishing Gemstones

Precious gemstone

Sapphire gemstone

Semiprecious gemstone

Some Archaeological Gemstones

Synthetic diamonds and gemstones

The Diamond Gemstone Market

Transition metals gemstones

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