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Lapis lazuli (UK: / ˌ l æ p ɪ s ˈ l æ z (j) ʊ l i, ˈ l æ ʒ ʊ-,-ˌ l i /; US: / ˈ l æ z (j) ə l i, ˈ l æ ʒ ə-,-ˌ l i /), or lapis for short, is a deep-blue metamorphic rock used as a semi-precious stone that has been prized since antiquity for its intense color.
The name moonstone derives from the stone's characteristic visual effect, called adularescence (or schiller), which produces a milky, bluish interior light. This effect is caused by light diffraction through alternating layers of orthoclase and albite within the stone.
[1] [2] [3] Certain rocks (such as lapis lazuli, opal, and obsidian) and occasionally organic materials that are not minerals (such as amber, jet, and pearl) may also be used for jewelry and are therefore often considered to be gemstones as well.
Unpolished sunstone. The optical effect is due to reflections from inclusions of red copper, hematite, or goethite, in the form of minute scales, which are hexagonal, rhombic, or irregular in shape, and are disposed parallel to the principal cleavage-plane.
The ancients also referred to lapis-lazuli as sapphire, which is likewise a blue stone, often speckled with shining pyrites giving it the appearance of being sprinkled with gold dust. It is composed of silica, alumina, and alkali and is an opaque substance easily engraved. Debate still continues as to which stone is precisely referred to in the ...
English: Large lapis lazuli specimen as seen at the National Museum of Natural History 2021 'Objects of Wonder' exhibit. This particular piece weighs over 100kg (about 250lbs). This particular piece weighs over 100kg (about 250lbs).
The Greek term for sapphire quite likely was instead used to refer to lapis lazuli. [72] During the Medieval Ages, European lapidaries came to refer to blue corundum crystal by "sapphire", a derivative of the Latin word for blue: sapphirus. [74] The sapphire is the traditional gift for a 45th wedding anniversary. [75]
Importing lapis lazuli by caravan across the desert from Afghanistan to Egypt was very expensive. Beginning in about 2500 BC, the ancient Egyptians began to produce their own blue pigment known as Egyptian blue by grinding silica , lime , copper , and alkalai , and heating it to 800 or 900 °C (1,470 or 1,650 °F).
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