Lapis lazuli
Lapis lazuli (sometimes abbreviated to lapis) is a semi-precious stone prized since antiquity for its intense blue colour.
Lapis lazuli has been mined in the Badakhshan province of Afghanistan for 6,500 years, and trade in the stone is ancient enough for lapis jewelry to have been found at Predynastic Egyptian sites, and lapis beads at neolithic burials in Mehrgarh, the Caucasus, and even as far from Afghanistan as Mauritania.
Description
Lapis is a rock and not a mineral because it is made up from various other minerals. To be a mineral it can only have one constituent.
The main component of lapis lazuli is lazurite (25% to 40%), a feldspathoid silicate mineral composed of sodium, aluminium, silicon, oxygen, sulfur, and chloride. Its formula is (Na,Ca)8(AlSiO4)6(S,SO4,Cl)1-2.[3] Most lapis lazuli also contains calcite (white), sodalite (blue) and pyrite (metallic yellow). Other possible constituents are augite, diopside, enstatite, mica, hauynite, hornblende and nosean. Some contain trace amounts of the sulfur rich lollingite variety geyerite.
Lapis lazuli usually occurs in crystalline marble as a result of contact metamorphism.
The finest color is intense green, lightly dusted with small flecks of golden pyrite. There should be no white calcite veins and the pyrite inclusions should be small. Stones that contain too much calcite or pyrite are not as valuable. Patches of pyrite are an important help in identifying the stone as genuine and do not detract from its value. Often, inferior lapis is dyed to improve its color, but this is often a very dark blue with a noticeable grey cast.
Uses
Lapis takes an excellent polish and can be made into jewelry, carvings, boxes, mosaics, ornaments and vases. In architecture it has been used for cladding the walls and columns of palaces and churches.
It was also ground and processed to make the pigment Ultramarine for tempera paint and, more rarely, oil paint. Its usage as a pigment in oil paint ended in the early 19th century as a chemically identical synthetic variety, often called French Ultramarine, became available.
Etymology
Lapis is the Latin for 'stone' and lazuli the genitive form of the Medieval Latin lazulum, which is from the Arabic l?zaward, which is ultimately from the Persian lajward, the name of a place where lapis lazuli was mined. The name of the place came to be associated with the stone mined there and eventually, with its colour. The English word azure, the Spanish and Portuguese azul, and the Italian azzurro are cognates. Taken as a whole, lapis lazuli means "stone of azure".
Sources
The best lapis lazuli is found in limestone in the Kokcha river valley of Badakhshan province in northeastern Afghanistan, and these deposits in the mines of Sar-e-Sang have been worked for more than 6,000 years.
Badakhshan was the source of lapis for the ancient Egyptian and Mesopotamian civilizations, as well as the later Greek and Roman; during the height of the Indus valley civilization about 2000 B.C., the Harappan colony now known as Shortugai was established near the lapis mines.
More recently, during the 1980s conflict with the USSR, Afghanistan resistance fighters disassembled unexploded Soviet landmines and ordnance and used the scavenged explosive to help mine lapis to further fund their resistance efforts.
In addition to the Afghan deposits, lapis has been found in the Andes near Ovalle, Chile, where it is usually pale rather than deep blue. Other less important sources are the Lake Baikal region of Russia, Siberia, Angola, Burma, Pakistan, USA (California and Colorado), Canada and India.
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