Photo of Lapis Lazuli in Processed & Rough Form
Lapis Lazuli is a mineral with a hardness of 6 out of 10 on the Mohs scale of mineral hardness [?]. These Variously structured gems are made of a variation materials, their full chemical compound being (Na,Ca)8(Al,Si)12O24(SO4)Cl2(OH)2.
Lapis lazuli is composed of several minerals in small quantities - augite, calcite, diopside, mica, hauynite, hornblende, pyrite. Because of this some experts consider it a rock, more than a mineral. The main ingredient of Lapis lazuli is Lazurite.
It has a uniform, massive, or sometimes granular appearance, with fairly distinct crystals. It is semi-opaque to opaque, with a surface that can take a good polish, like jade.
It has a vitreous to greasy luster. It is very sensitive to pressure and high temperatures, hot baths, acids, and alkalies. On contact with a minute drop of hydrochloric acid, lapis lazuli immediately gives off an odor of hydrogen sulphide, which is like the smell of rotten eggs.
It is a strong but lively blue, sometimes with a hint of violet. The particular, very attractive color and speckling with minute crystals of pyrite give lapis lazuli an unmistakable appearance. In the best quality the color is regularly distributed, but it is usually spotted or striped. The matrix rock is white dolomitic marble. It often contains grayish or off-white patches or veins, consisting of distinct, interwoven crystals which are minutely fringed at the edge of the patches, permeated with the minute crystals of blue. The presence of white patches reduces the gem's value. The most highly prized varieties are those which are uniformly colored, preferably without a violet tinge.
Mineable deposits are rare. For centuries the most important deposit with the best qualities has been in the West Hindu Kush mountains of Afghanistan near the source of the river Amu-Darja, where it has been mined since remote antiquity. Lapis lazuli is mined under primitive conditions and in difficult terrain where it is present as an irregular occurrence in limestone. The Russian deposits are at the south west end of Baikal Lake. Chile supplies lower quality stones with many white spots of calcite. The deposits come from north of Santiago in the Coquimbo province.
Much smaller quantities of lapis come from Siberia, Burma, Pakistan, Angola, USA, and Canada.
Called lapis for short, sometimes lazurite.
Lapis lazuli can be confused with azurite, dumortierite, lazulite, sodalite, and glass imitations.
The specific gravity [?] for Lapis Lazuli is 2.8, its refractive index [?] is 1.50 (mea, and its double refraction [?] is None.
History
Lapis lazuli takes its name from the medieval Latin "lapis lazulus," from the Arabic word "lazward," from which the word "azure" comes. But according to the description of Pliny the Elder, ancient Romans called it "sapphirus," but this name was subsequently applied to sapphire, the blue variety of corundum.
Lapis was used for jewelry in antiquity. During the Middle Ages, it was also used as a pigment to produce aquamarine. Some castles have wallpanels and columns covered in lapis. At one time lapis was much used for sealstones. The Egyptians used it for their cylindrical seals and most likely obtained their supplies from the Afghanistan mountains.
Industrial Usages
Lapis lazuli is one of the most valuable semiopaque ornamental materials, worth about the same as good quality turquoise and the better jades (including imperial jade).
Well-distributed fine pyrite is advantageous and is taken to show genuineness, and do not detract from its value. Too much pyrite causes a dull, greenish tint.
In Chilean and Russian stones, the protruding white calcite diminishes the value. Chilean lapis is used for carvings and ornamental objects.
Lapis is made into spherical or curved beads and even faceted, polyhedral ones, in which the flat facets can take a very good polish. It is also fashioned into carved gems, boxes, mosaics, small ornaments, vases, and figurines, the largest of which may be several centimeters in size.
The finely-grained, gray-brown jasper from Nunkirchen is colored with prussian blue and sold as an imitation under the name "Swiss lapis."
In 1954 a synthetic grainy spinel, colored with cobalt oxide, with a good lapis color made an appearance on the market. Inclusions of thin gold pieces simulated the pyrite and improved the character of the genuine stone. This is called synthetic lapis lazuli. As the pyrite consists of ground fragments, it never displays the characteristic crystal form.
Lapis lazuli was and is much imitated, by glass, sometimes containing minute specks of metal to simulate pyrite; by stained chalcedony, and by a deep blue sintered aggregate of minute grains of synthetic spinel.
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