Diopside

Diopside
Diopside – Bellecombe, Châtillon, Aosta Valley, Italy
General
CategoryInosilicate mineral
Formula
(repeating unit)
MgCaSi2O6
IMA symbolDi[1]
Strunz classification9.DA.15
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/c
Unit cella = 9.746 Å, b = 8.899 Å
c = 5.251 Å; β = 105.79°; Z = 4
Identification
ColorCommonly light to dark green; may be blue, brown, colorless, white to snow white, grey, pale violet
Crystal habitShort prismatic crystals common, may be granular, columnar, massive
TwinningSimple and multiple twins common on {100} and {001}
CleavageDistinct/good on {110}
FractureIrregular/uneven, conchoidal
TenacityBrittle
Mohs scale hardness5.5–6.5
LusterVitreous to dull
Streakwhite
Specific gravity3.278
Optical propertiesBiaxial (+)
Refractive indexnα= 1.663 – 1.699, nβ= 1.671 – 1.705, nγ= 1.693 – 1.728
Birefringenceδ = 0.030
2V angleMeasured: 58° to 63°
DispersionWeak to distinct, r>v
Melting point1391 °C
References[2][3][4]

Diopside is a monoclinic pyroxene mineral with composition MgCaSi
2
O
6
. It forms complete solid solution series with hedenbergite (FeCaSi
2
O
6
) and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull green crystals in the monoclinic prismatic class. It has two distinct prismatic cleavages at 87 and 93° typical of the pyroxene series. It has a Mohs hardness of six, a Vickers hardness of 7.7 GPa at a load of 0.98 N,[5] and a specific gravity of 3.25 to 3.55. It is transparent to translucent with indices of refraction of nα=1.663–1.699, nβ=1.671–1.705, and nγ=1.693–1.728. The optic angle is 58° to 63°.

  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. ^ C. D. Gribble, ed. (1988). "The Silicate Minerals". Rutley's Elements of Mineralogy (27th ed.). London: Unwin Hyman Ltd. p. 378. ISBN 0-04-549011-2.
  3. ^ Mindat page for Diopside
  4. ^ Handbook of Mineralogy
  5. ^ M M Smedskjaer; M Jensen; Y-Z Yue (2008). "Theoretical calculation and measurement of the hardness of diopside". Journal of the American Ceramic Society. 91 (2): 514–518. doi:10.1111/j.1551-2916.2007.02166.x.