Grossular

Grossular
Grossular dodecahedron, 7 mm across, from Coahuila, Mexico
General
CategoryNesosilicate
Formula
(repeating unit)
Ca3Al2(SiO4)3
IMA symbolGrs[1]
Strunz classification9.AD.25
Crystal systemCubic[2]
Crystal classHexoctahedral (m3m)
H-M Symbol: (4/m 3 2/m)
Space groupIa3d
Identification
Colorlight to dark green, light to dark yellow to reddish brown, brown, orange, red, yellow, green, white, occasionally translucent to opaque pink. It is also but rarely found in colorless form[2]
Cleavagenone
Fractureconchoidal to uneven[2]
Mohs scale hardness6.5 to 7[2]
Lustergreasy to vitreous[2]
StreakBrown
Specific gravity3.61 (+.15/−.04)
Polish lustervitreous[2]
Optical propertiesSingle refractive, often anomalous double refractive[2]
Refractive index1.740 (+.12/−.04)[2]
Birefringencenone
Pleochroismnone
Dispersion.028
Ultraviolet fluorescencenear colorless to light green – inert to weak orange in longwave and weak yellow-orange in shortwave; yellow – inert to weak orange in longwave and shortwave[2]
Absorption spectraHessonite sometimes shows bands at 407 and 430 nm
Major varieties
Hessoniteyellow-red to reddish-orange
Tsavoriteintense green to yellowish green
Leuco-garnettransparent and colorless[3]
Rosolitetranslucent to opaque pink grossularite crystals in marble from Mexico

Grossular is a calcium-aluminium species of the garnet group of minerals. It has the chemical formula of Ca3Al2(SiO4)3 but the calcium may, in part, be replaced by ferrous iron and the aluminium by ferric iron. The name grossular is derived from the botanical name for the gooseberry, grossularia, in reference to the green garnet of this composition that is found in Siberia. Other shades include cinnamon brown (cinnamon stone variety), red, and yellow. Grossular is a gemstone.

In geological literature, grossular has often been called grossularite. Since 1971, however, use of the term grossularite for the mineral has been discouraged by the International Mineralogical Association.[4]

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b c d e f g h i GIA Gem Reference Guide; Gemological Institute of America; 1995; ISBN 0-87311-019-6
  3. ^ Cite error: The named reference MGKGross was invoked but never defined (see the help page).
  4. ^ International Mineralogical Association (1971). "International Mineralogical Association: Commission on new minerals and mineral names" (PDF). Mineralogical Magazine. 38 (293): 102–105. Bibcode:1971MinM...38..102.. doi:10.1180/minmag.1971.038.293.14.