Garnet

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Garnet
GarnetCrystalUSGOV.jpg
General
CategoryNesosilicate
Formula
(repeatin unit)
The general formula X3Y2(SiO4)3
Creestal seestemCubic rhombic dodecahedron, icositetrahedron
Identification
Colourvirtually aw colours
Creestal habitRhombic dodecahedron or cubic
CleavageIndistinct
Fracturconchoidal tae uneven
Mohs scale haurdness6.5–7.5
Skinklevitreous tae resinous
StreakWhite
Speceefic gravity3.1–4.3
Polish skinklevitreous tae subadamantine[1]
Optical propertiesSingle refractive, eften anomalous double refractive[1]
Refractive index1.72–1.94
BirefringenceNone
PleochroismNone
Major varieties
PyropeMg3Al2Si3O12
AlmandineFe3Al2Si3O12
SpessartineMn3Al2Si3O12
AndraditeCa3Fe2Si3O12
GrossularCa3Al2Si3O12
UvaroviteCa3Cr2Si3O12

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

Aw species o garnets possess seemilar 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.