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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.
Lazurite is a pigment (opalescent) and has a bright blue streak (especially as a component of the semiprecious stone lapis lazuli). Many hauynes have a white or pale blue streak and are translucent. The difference might be a consequence of the redox state (sulfate to sulfide ratio). [8] [14]
Refractive index readings of faceted gems can range around α = 1.651, β = 1.668, and γ = 1.689, with a biaxial positive birefringence of 0.037–0.038. With decreasing magnesium and increasing iron concentration, the specific gravity, color darkness and refractive indices increase, and the β index shifts toward the γ index.
Prasiolite is a rare stone in nature; artificial prasiolite is produced from amethyst. [4] Most amethyst will turn yellow or orange when heated, producing heat-treated amethysts which are often marketed as citrine , but some amethyst will turn green when treated.
Carnelian (also spelled cornelian) [3] is a brownish-red mineral commonly used as a semiprecious stone.Similar to carnelian is sard, which is generally harder and darker; the difference is not rigidly defined, and the two names are often used interchangeably.
Taaffeite (/ ˈ t ɑː f aɪ t /; BeMgAl 4 O 8) is a mineral, named after its discoverer Richard Taaffe (1898–1967) who found the first sample, a cut and polished gem, in October 1945 in a jeweler's shop in Dublin, Ireland. [4] [5] As such, it is the only gemstone to have been initially identified from a faceted stone.
Lustre (British English) or luster (American English; see spelling differences) is the way light interacts with the surface of a crystal, rock, or mineral.The word traces its origins back to the Latin lux, meaning "light", and generally implies radiance, gloss, or brilliance.
It was first described in 1828 at Mount Baldo, Trento Province, Italy, and named from the Greek pektos – "compacted" and lithos – "stone". [ 3 ] [ 4 ] It occurs as a primary mineral in nepheline syenites , within hydrothermal cavities in basalts and diabase and in serpentinites in association with zeolites , datolite , prehnite , calcite ...