Monticellite

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Monticellite-Kirschsteinite
Monticellite-D1056b.jpg
Sharp, freestanding monticellite crystals to over 1 cm, perched on semilustrous brown vesuvianite (idocrase) crystals. Remnant calcite matrix is blue-gray.
General
Category Nesosilicate
Formula Ca(Mg,Fe)SiO4
IMA symbol Mtc – Kir [1]
Strunz classification 9.AC.10
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Pbnm
Identification
Colourcolourless or grey
Cleavage {010}
Mohs scale hardness5.5
Specific gravity 3.05 – 3.27
Refractive index α = 1.638 – 1.654,
β = 1.646 – 1.664,
γ = 1.650 – 1.674
Melting point 1503 °C
References [2]

Monticellite and kirschsteinite (commonly also spelled kirschteinite [3] ) are gray silicate minerals of the olivine group with compositions Ca Mg Si O 4 and CaFeSiO4, respectively. Most monticellites have the pure magnesium end-member composition but rare ferroan monticellites and magnesio-kirschsteinite are found with between 30 and 75 mol.% of the iron end member. Pure kirschsteinite is only found in synthetic systems. Monticellite is named after Teodoro Monticelli, an Italian mineralogist (1759–1845). Kirschsteinite is named after Egon Kirschstein, a German geologist.

Contents

Like other members of the group monticellite and kirschsteinite have orthorhombic unit cells (space group Pbnm) shown in Figure 1. Iron and magnesium ions are located on the M1 inversion sites and calcium ions occupy the M2 site on mirror planes. The unit cell is somewhat larger than for the calcium free olivines forsterite and fayalite with

a = 0.4815  nm,
b = 1.108 nm and
c = 0.637 nm,

and for monticellite

a = 0.4875 nm,
b = 1.1155 nm and
c = 0.6438 nm.

References

  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. Mineralienatlas
  3. Klein and Hurlbut Manual of Mineralogy 20th ed., p. 373