domingo, 21 de julho de 2013

Lapis lazuli

Lapis lazuli


"Lapis" redirects here. For other uses, see Lapis (disambiguation).
Lapis lazuli
Lapis lazuli block.jpg
A polished specimen of lapis lazuli.
General
Category Rock
Formula
(repeating unit)		 mixture of minerals
Identification
Color Blue, mottled with white calcite and brassy pyrite
Crystal habit Compact, massive
Crystal system None, as lapis is a rock. Lazurite, the main constituent, frequently occurs as dodecahedra
Cleavage None
Fracture Uneven-Conchoidal
Mohs scale hardness 5–5.5
Luster dull
Streak light blue
Specific gravity 2.7–2.9
Refractive index 1.5
Other characteristics The variations in composition cause a wide variation in the above values.
Lapis lazuli specimen (rough), Afghanistan
Lapis lazuli (/ˈlæpɪs ˈlæzjʉlaɪ/ or /ˈlæzjʉli/ LAP-iss LAZ-zew-ly/lee,[1]) (sometimes abbreviated to lapis) is a relatively rare semi-precious stone that has been prized since antiquity for its intense blue color.
Lapis lazuli was being mined in the Badakhshan province of Afghanistan as early as the 3rd millennium BC,[2] and there are sources that are found as far east as in the region around Lake Baikal in Siberia[citation needed]. Trade in the stone is ancient enough for lapis jewelry to have been found at Predynastic Egyptian and ancient Sumerian sites, and as lapis beads at neolithic burials in Mehrgarh, the Caucasus, and even as far from Afghanistan as Mauritania.[3]

Contents

Description

Lapis lazuli is a rock, largely formed from the mineral lazurite.[4]
The main component of lapis lazuli is lazurite (25% to 40%), a feldspathoid silicate mineral with the formula (Na,Ca)8(AlSiO4)6(S,SO4,Cl)1-2.[5] Most lapis lazuli also contains calcite (white), sodalite (blue), and pyrite (metallic yellow). Other possible constituents: augite; diopside; enstatite; mica; hauynite; hornblende, and nosean. Some lapis lazuli contains trace amounts of the sulfur-rich löllingite variety geyerite.
Lapis lazuli usually occurs in crystalline marble as a result of contact metamorphism.

Etymology

Lapis is the Latin word for "stone" and lazuli is the genitive form of the Medieval Latin lazulum, which is taken from the Arabic لازورد lāzaward, itself from the Persian لاژورد lāžaward, the name of a place where lapis lazuli was mined.[6][7] Taken as a whole, lapis lazuli means "stone of Lāzhward".
The name of the place came to be associated with the stone mined there and, eventually, with its color. The French azur, the Italian azzurro, the Polish lazur, Romanian azur and azuriu, and the Portuguese and Spanish azul, Hungarian azúr are cognates.

Sources

Lapis lazuli is found in limestone in the Kokcha River valley of Badakhshan province in northeastern Afghanistan, where the Sar-e-Sang mine deposits have been worked for more than 6,000 years.[8] Afghanistan was the source of lapis for the ancient Egyptian and Mesopotamian civilizations, as well as the later Greeks and Romans. During the height of the Indus valley civilization about 2000 BC, the Harappan colony now known as Shortugai was established near the lapis mines.[3]
In addition to the Afghan deposits, lapis has been extracted for many years in the Andes (near Ovalle, Chile), the Lake Baikal region of Russia[citation needed]; Siberia; Angola; Argentina; Burma; Pakistan; Canada; India; and in the USA in California and Colorado.

Alternatives

Lapis lazuli is commercially "synthesized" (actually simulated) by the Gilson process, using artificial ultramarine and hydrous zinc phosphates.[9] It may be substituted by spinel or sodalite, or by dyed jasper or howlite.[10]

Uses

Lapis takes an excellent polish and can be made into jewelry, carvings, boxes, mosaics, ornaments, and vases. 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 when a chemically identical synthetic variety, often called French ultramarine, became available.

Historical usage

In ancient Egypt, lapis lazuli was a favorite stone for amulets and ornaments such as scarabs; it was also used in ancient Mesopotamia by the Sumerians, Akkadians, Assyrians, and Babylonians for seals and jewelry. In the Epic of Gilgamesh; the oldest known story in human history, lapis lazuli is referenced several times. Lapis jewelry has been found at excavations of the Predynastic Egyptian site Naqada (3300–3100 BC), and powdered lapis was used as eyeshadow by Cleopatra.[3] In ancient Mesopotamia, lapis artifacts can be found in great abundance, with many notable examples having been excavated at the 25th-century BC Statue of Ebih-Il, discovered in ancient Mari in Syria, uses lapis lazuli inlays that were imported from as far east as Afghanistan.[11]
In ancient times, lapis lazuli was known as sapphire,[12] which is the name that is used today for the blue corundum variety sapphire. It has also been used in the Taj Mahal in India.

Color

The intense blue color is due to the presence of the S3- radical anion in the crystal.[13] An electronic excitation of one electron from the highest doubly filled molecular orbital (No. 24) into the lowest singly occupied orbital (No. 25)[14] results in a very intense absorption line at λmax ~617 nm.

Gallery

  • A Mesopotamian lapis lazuli pendant circa 2900 BC.
  • A 11 cm (4.3 in)-long lapis lazuli dove studded with gold pegs. Elamite. Dated 1200 BC from Susa, Iran
  • An elephant carving on high-quality lapis lazuli, that includes gold-colored pyrite, is a rare example of Mughal inspired art. (length: 8 cm (3.1 in))
  • Carved lapis lazuli mountain scene, from the Chinese Qing Dynasty (1644–1912).
  • The Girl with a Pearl Earring (1665) by Johannes Vermeer is painted with the exorbitantly expensive pigment lapis lazuli, or natural ultramarine
  • Close-up of the lapis lazuli inlays in the 25th-century BC Statue of Ebih-Il

See also

Notes

  1. ^ The New Penguin English Dictionary, 2000
  2. ^ Moorey, Peter Roger (1999). Ancient Mesopotamian Materials and Industries: the Archaeological Evidence. Eisenbrauns. pp. 86–87. ISBN 978-1-57506-042-2.
  3. ^ a b c Bowersox & Chamberlin 1995
  4. ^ Mindat entry relating to lapis lazuli
  5. ^ Mindat – Lazurite
  6. ^ Senning, Alexander (2007). "lapis lazuli (lazurite)". Elsevier's Dictionary of Chemoetymology. Amsterdam: Elsevier. p. 224. ISBN 978-0-444-52239-9.
  7. ^ Weekley, Ernest (1967). "azure". An Etymological Dictionary of Modern English. New York: Dover Publications. p. 97.
  8. ^ Oldershaw 2003
  9. ^ Read, Peter (2005). Gemmology, Elsevier, p. 185. ISBN 0-7506-6449-5
  10. ^ Lapis lazuli, Gemstone Buzz.
  11. ^ Claire, Iselin. "Ebih-Il, the Superintendent of Mari". Musée du Louvre. Retrieved 10 October 2012.
  12. ^ Schumann, Walter (2006) [2002]. "Sapphire". Gemstones of the World. trans. Annette Englander & Daniel Shea (newly revised & expanded 3rd ed.). New York: Sterling. p. 102. "In antiquity and as late as the Middle Ages, the name sapphire was understood to mean what is today described as lapis lazuli."
  13. ^ E. Boros, M. J. Earle, M. A. Gilea, A. Metlen, A.-V. Mudring, F. Rieger, A. J. Robertson, K. R. Seddon, A. A. Tomaszowska, L. Trusov and J. S. Vyle, "On the dissolution of non-metallic solid elements (sulfur, selenium, tellurium and phosphorus) in ionic liquids," Chem. Comm., 2010, 46, 716–718. doi:10.1039/b910469k
  14. ^ H. S. Rzepa, "Lapis lazuli: the Colour of Ultramarine." Accessed: 2011-03-06. (Archived by WebCite® at http://www.webcitation.org/5wyiNxh3B)

References

  • Bowersox, Gary W.; Chamberlin, Bonita E. (1995). Gemstones of Afghanistan. Tucson, AZ: Geoscience Press..
  • Oldershaw, Cally (2003). "Lapis Lazuli". Firefly Guide to Gems. Toronto: Firefly Books..
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