Lapis Lazuli is a beautiful deep blue stone, although its exact color varies because it is a
mixture of minerals whose proportions vary. It has been known since ancient times, its name
coming from a Persian word lazhward meaning blue, and its historical source being high in the
Badakhshan mountains in north-eastern Afghanistan where it has been worked for over 6,000
years. It is opaque and slightly soft, therefore is almost always cut en cabochon, or as beads,
rather than being faceted. It was also in ancient times sometimes called sapphirus, meaning
blue. The word lapis is latin meaning stone.
Coloration
Although lapis, as it is often called, is deep blue, its color does show variation depending
on its source and exact composition. Some material is lighter blue or greenish blue, some a
rich purple blue, almost black. The best color is an intense deep blue. The pigment
ultramarine used to be made from crushed lapis lazuli, and probably provides the best
description of its most desirable color. It usually contains golden colored flecks of pyrite.
These are normally regarded as increasing the desirability, and are an indication of
authenticity. Lapis also contains calcite, which sometimes shows as white flecks. These flecks
are regarded as decreasing the beauty and desirability of lapis, especially if they are large
or numerous, although tiny flecks can help to indicate that it is genuine. The deep blue color
is mainly due to the presence of hauynite.
Sources
Apart from its traditional source in Afghanistan, lapis lazuli is also found in Chile, Siberia,
Burma, and California.
Technical Characteristics
Lapis lazuli is not a mineral but a rock which is complex aggregate (mixture) of other
minerals. These minerals are:
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Hauynite Chemical Composition:
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(NaCa)4 8(S3So2)1 2(Al6Si6O24)
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Sodalite Chemical Composition:
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Na8Cl2(Al6Si6O24)
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Noselite Chemical Composition:
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Na8(SO2)(Al6Si6O24)
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Lazurite Chemical Composition:
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Amorphous mixture of hauynite and sodalite. |
According to Webster's Gems, these four minerals all crystallise in the cubic system,
and are members of a group of rock-forming minerals known as feldpathoids, which are
produced when the silica content of the host rock is insufficient to form completely true
feldspar. Calcite is always present.
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Hardness:
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5.5
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Specific Gravity:
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2.75 to 2.9
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Refractive Index (R.I.):
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1.5 Variable
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