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Gemstones are basically categorized based on their crystal structure, specific gravity, refractive index, and other optical properties, such as pleochroism. The physical property of "hardness" is defined by the irregular Mohs scale of mineral hardness. Gemologists study these factors while valuing or appraising cut and polished gemstones.
The specific gravity increases with the iron content, and very pure jadeite has a specific gravity of 3.25. [8] The luster is vitreous, or pearly on exposed cleavage surfaces, and the streak is colorless. [9] Jadeite is translucent to transparent. [8] Jadeite is characterized by its green color and tough aggregates of compact fibrous crystals.
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.
Sugilite crystallizes in the hexagonal system with prismatic crystals. The crystals are rarely found and the form is usually massive. The crystals are rarely found and the form is usually massive. It has a Mohs hardness of 5.5–6.5 and a specific gravity of 2.75–2.80.
In more recent history, moonstone became popular during the Art Nouveau period; French goldsmith René Lalique and many others created a large quantity of jewellery using this stone. [5] The moonstone is the Florida State Gemstone; it was designated as such in 1970 to commemorate the Moon landings, which took off from Kennedy Space Center ...
Lonsdaleite was first identified in 1967 from the Canyon Diablo meteorite, where it occurs as microscopic crystals associated with ordinary diamond. [5] [6] It is translucent and brownish-yellow and has an index of refraction of 2.40–2.41 and a specific gravity of 3.2–3.3 .
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.
Phenakite or phenacite is a fairly rare nesosilicate mineral consisting of beryllium orthosilicate, Be 2 Si O 4.Occasionally used as a gemstone, phenakite occurs as isolated crystals, which are rhombohedral with parallel-faced hemihedrism, and are either lenticular or prismatic in habit: the lenticular habit is determined by the development of faces of several obtuse rhombohedra and the ...
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