Garnet

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Garnet
GarnetCrystalUSGOV.jpg
General
Category Nesosilicate
Formula
(repeating unit)
The general formula X3Y2(SiO4)3
Identification
Color virtually aw colours
Crystal habit Rhombic dodecahedron or cubic
Crystal seestem Cubic rhombic dodecahedron, icositetrahedron
Cleavage Indistinct
Fractur conchoidal tae uneven
Mohs scale hairdness 6.5–7.5
Luster vitreous tae resinous
Streak White
Specific gravity 3.1–4.3
Polish luster vitreous tae subadamantine[1]
Optical properties Single refractive, eften anomalous double refractive[1]
Refractive index 1.72–1.94
Birefringence None
Pleochroism None
Major varieties
Pyrope Mg3Al2Si3O12
Almandine Fe3Al2Si3O12
Spessartine Mn3Al2Si3O12
Andradite Ca3Fe2Si3O12
Grossular Ca3Al2Si3O12
Uvarovite Ca3Cr2Si3O12

Garnets /ˈɡɑːrnət/ are a group o silicate minerals that hae been uised syne the Bronze Age as gemstanes an abrasives.[note 1]

Aw species o garnets possess similar pheesical properties an crystal forms, but differ in chemical composition. The different species are pyrope, almandine, spessartine, grossular (varieties o which are hessonite or cinnamon-stane an tsavorite), uvarovite an andradite. The garnets mak up twa solid solution series: pyrope-almandine-spessarite an uvarovite-grossular-andradite.

Notes[eedit | eedit soorce]

  1. The wird garnet comes frae 14t‑century Middle Inglis wird gernet meanin 'dark reid,' frae the Laitin granatus, frae granum ('grain, seed') + suffix atus, possibly a reference tae mela granatum or even pomum granatum ('pomegranate',[2] scientific name: Punica granatum), a plant whose fruits contain abundant an vivid reid arils, are similar in shape, size, an colour tae some garnet crystals.[3]

References[eedit | eedit soorce]

  1. 1.0 1.1 Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
  2. pomegranate. Online Etymology Dictionary. Retrieved on 2011-12-25.
  3. garnet. Online Etymology Dictionary. Retrieved on 2011-12-25.