Geikielite

Geikielite
Crystals of geikielite from the Maxwell quarry, Chelsea, Outaouais, Québec, Canada
General
Category	Oxide mineral
Formula (repeating unit)	MgTiO3
IMA symbol	Gk[1]
Strunz classification	4.CB.05
Crystal system	Trigonal
Crystal class	Rhombohedral (3) (same H-M symbol)
Space group	R3
Unit cell	a = 5.05478(26) Å c = 13.8992(7) Å; Z = 6
Identification
Color	Black, ruby red uncommon; red internal reflections
Crystal habit	Tabular prismatic crystals, also as finely granular masses
Cleavage	Good on {1011}
Mohs scale hardness	5 - 6
Luster	Sub-metallic
Streak	Purplish brown
Diaphaneity	Opaque to translucent
Specific gravity	3.79 - 4.2
Optical properties	Uniaxial (-)
Refractive index	nω = 2.310 - 2.350 nε = 1.950 - 1.980
Birefringence	δ = 0.360 - 0.370
Pleochroism	Weak, O = pinkish red, E = brownish to purplish red
References	[2][3][4]

Geikielite is a magnesium titanium oxide mineral with formula: MgTiO₃. It is a member of the ilmenite group. It crystallizes in the trigonal system forming typically opaque, black to reddish black crystals.

It was first described in 1892^[5] for an occurrence in the Ceylonese gem bearing gravel placers. It was named for Scottish geologist Sir Archibald Geikie (1835–1924).^[4] It occurs in metamorphosed impure magnesian limestones, in serpentinite derived from ultramafic rocks, in kimberlites and carbonatites. Associated minerals include rutile, spinel, clinohumite, perovskite, diopside, serpentine, forsterite, brucite, hydrotalcite, chlorite and calcite.^[2]

• Ghiorso, Mark S. (1990). "Thermodynamic properties of hematite — Ilmenite — Geikielite solid solutions". Contributions to Mineralogy and Petrology. 104 (6): 645–667. Bibcode:1990CoMP..104..645G. doi:10.1007/BF01167285. S2CID 98522254.
• Reynard, B.; Guyot, F. (1994). "High-temperature properties of geikielite (MgTiO₃-ilmenite) from high-temperature high-pressure Raman spectroscopy ? Some implications for MgSiO3-ilmenite". Physics and Chemistry of Minerals. 21 (7): 441. Bibcode:1994PCM....21..441R. doi:10.1007/BF00202274. S2CID 96095190.
• Baura-Peña, M. P.; Martínez-Lope, M. J.; García-Clavel, M. E. (1991). "Synthesis of the mineral geikielite MgTiO₃". Journal of Materials Science. 26 (16): 4341. Bibcode:1991JMatS..26.4341B. doi:10.1007/BF00543648. S2CID 94170430.
• Robie, Richard A.; Haselton, H.T.; Hemingway, Bruce S. (1989). "Heat capacities and entropies at 298.15 K of MgTiO₃(geikielite), ZnO (zincite), and ZnCO₃ (smithsonite)". The Journal of Chemical Thermodynamics. 21 (7): 743. doi:10.1016/0021-9614(89)90058-X.
• Gieré, Reto (1987). "Titanian clinohumite and geikielite in marbles from the Bergell contact aureole". Contributions to Mineralogy and Petrology. 96 (4): 496–502. Bibcode:1987CoMP...96..496G. doi:10.1007/BF01166694. S2CID 86861792.
• Parthasarathy, G. (2007). "Electrical resistivity of nano-crystalline and natural MgTiO₃−geikielite at high-pressures up to 8 GPa". Materials Letters. 61 (21): 4329–4331. doi:10.1016/j.matlet.2007.01.097.
• Mitchell, Jeremy N.; Yu, Ning; Sickafus, Kurt E.; Nastasi, Michael A.; McClellan, Kenneth J. (1998). "Ion irradiation damage in geikielite (MgTiO₃)". Philosophical Magazine A. 78 (3): 713. Bibcode:1998PMagA..78..713M. doi:10.1080/01418619808241931.
• Chao, G. Y.; Hounslow, A. W. (June 1967). "Geikielite; a new Canadian occurrence". The Canadian Mineralogist. 9 (1): 95–100.