Knorringite

Knorringite is a mineral species belonging to the garnet group, and forms a series with the species pyrope. It was discovered in 1968 in the Kao kimberlite pipe in the Butha-Buthe District of Lesotho and is named after Oleg Von Knorring, a professor of mineralogy at the University of Leeds in England.[2][3]

Knorringite
General
Categorygarnet, nesosilicate
Formula
(repeating unit)		Mg3Cr2(SiO4)3
IMA symbolKrr[1]
Strunz classification9.AD.25
Crystal systemCubic
Crystal classHexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space groupIa3d
Unit cella = 11.59 Å; Z = 8
Identification
ColorBluish green
Crystal habitMassive and as minute grains
CleavageNone
Mohs scale hardness6 - 7
LusterVitreous
DiaphaneitySemitransparent
Specific gravity3.756
Optical propertiesIsotropic
Refractive indexn = 1.803
References[2][3][4]

Synthetic knorringite has the pure endmember formula Mg3Cr2(SiO4)3.[3] As knorringite is a member of the knorringite - pyrope series, natural samples contain variable aluminium in the chromium site.[5] Knorringite is a greenish blue color with a Mohs scale of mineral hardness of six to seven.

It occurs as a rare component within ultramafic nodules in kimberlites in association with olivine, enstatite, chrome diopside, chromian pyrope, chromian spinel, ilmenite, perovskite, zircon, diamond, omphacite, rutile, carbonates and micas. It has been reported from the Red Ledge mine in Nevada County, California in addition to the type location in Lesotho.[3]

Knorringite is a tracer mineral in the search for diamonds in kimberlite pipes.

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. Mindat.org
  3. Handbook of Mineralogy
  4. Webmineral description
  5. Nixon, P.H. and G. Hornung (1968) A new chromium garnet end member, knorringite, from kimberlite, Amer. Mineral., 53, 1833 - 1840


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