Lapis lazuli

Lapis lazuli, also known simply as "lapis", is a blue metamorphic rock that has been used by people as a gemstone, sculpting material, and ornamental material for thousands of years. Its name was derived from the Latin word "lapis" meaning "stone", and from the Arabic and Persian word "lazaward". "Lazaward" was the Persian name for lapis stone, as well as the name of its mining location. In other parts of the world, words for 'blue' were named after the color of lapis, including the English word "azure"; Italian "azzurro"; Polish "azur"; Spanish "azur" and Romanian "azuriu".

Unlike most other gem materials, lapis lazuli is not a mineral. Instead, it is a rock composed of multiple minerals. It is composed mostly of lazurite, a blue silicate mineral of the sodalite group, typically at levels of 30-40%. In addition to lazurite, specimens of lapis lazuli usually contain calcite and pyrite. Sodalite, hauyne, wollastonite, afghanite, mica, dolomite, diopside, and a diversity of other minerals might also be present. To be called "lapis lazuli", a rock must have a distinctly blue colour and contain at least 25% blue lazurite. Calcite (white) is often the second most abundant mineral present in lapis lazuli as layers, fractures, or mottling. It can also be finely intermixed with lazurite to produce a rock with a faded denim colour. Pyrite usually occurs in lapis lazuli as tiny, randomly spaced grains with a contrasting gold colour. Dependent on metamorphic history and protolith chemistry, other common minerals in lapis include; augite, diopside, enstatite, mica, hornblende, and nosean.

Lapis lazuli forms near igneous intrusions where limestone or marble has been altered by contact metamorphism or hydrothermal metamorphism. In these rocks, lazurite replaces portions of the host rock and often preferentially develops within certain bands or layers. Afghanistan is the world's leading source of lapis lazuli. Some parts of the country have been actively mined for thousands of years.

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Fig.1: Sar-e-Sang valley, Afghanistan.

Fig.2: Lapis Lazuli sample, Afghanistan.

Bibliography

• David Shelley (1983): Igneous and metamorphic rocks under the microscope. Campman & Hall editori.
• E. WM. Heinrich (1956): Microscopic Petrografy. Mcgraw-hill book company,inc
• S. W Faryad (2002). Metamorphic conditions and fluid compositions of scapolite-bearing rocks from the lapis lazuli deposit at Sare Sang, Afghanistan. Journal of Petrology, 43(4), 725-747.

Photo
Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)	Blue lazurite (isotropic, with some anomalously anisotropic blue zones), pyroxene (high interference colors) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. XPL image, 2x (Field of view = 7mm)	Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)
Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)	Blue lazurite (isotropic, with some anomalously anisotropic blue zones), pyroxene (high interference colors) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. XPL image, 2x (Field of view = 7mm)	Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)
Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)	Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)	Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)
Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)	Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)	Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)
Blue lazurite (isotropic, with some anomalously anisotropic blue zones), pyroxene (high interference colors) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. XPL image, 2x (Field of view = 7mm)	Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)	Blue lazurite (isotropic, with some anomalously anisotropic blue zones), pyroxene (high interference colors) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. XPL image, 2x (Field of view = 7mm)
Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)	Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)	Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)
Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)	Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)	Blue lazurite (isotropic, with some anomalously anisotropic blue zones), pyroxene (high interference colors) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. XPL image, 2x (Field of view = 7mm)
Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)	Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 2x (Field of view = 7mm)	Blue lazurite (isotropic, with some anomalously anisotropic blue zones), pyroxene (high interference colors) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. XPL image, 2x (Field of view = 7mm)
Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 10x (Field of view = 2mm)	Blue lazurite (isotropic, with some anomalously anisotropic blue zones), pyroxene (high interference colors) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. XPL image, 10x (Field of view = 2mm)	Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 10x (Field of view = 2mm)
Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 10x (Field of view = 2mm)	Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 10x (Field of view = 2mm)	Blue lazurite, pyroxene (beige), pyrite (black) and calcite crystals in a Lapis Lazuli from Sar-e-Sang, Afghanistan. PPL image, 10x (Field of view = 2mm)