Kochite

Kochite
General
CategorySorosilicates
Rosenbuschite group
Formula(Na,Ca)3Ca2(Mn,Ca)ZrTi[(F,O)4(Si2O7)2]
IMA symbolKoh[1]
Crystal systemTriclinic
Crystal classPinacoidal (1)
(same H-M symbol)
Space groupP1
Unit cella = 10.03, b = 11.33
c = 7.202 [Å]; α = 90.19°
β = 100.33°, γ = 111.55°; Z = 2
Identification
ColorColorless to light brown
Crystal habitAcicular to lath-shaped prismatic crystals
Cleavage{100} perfect
FractureUneven
TenacityBrittle
Mohs scale hardness5
LusterVitreous
StreakWhite
DiaphaneityTransparent
Specific gravity3.32
Optical propertiesBiaxial (+)
Refractive indexnα=1.684, nβ=1.695, nγ=1.718
Birefringence0.0340
Pleochroismweak, colorless to pale brownish-yellow
References[2][3][4]

Kochite is a rare silicate mineral with chemical formula of (Na,Ca)3Ca2(Mn,Ca)ZrTi[(F,O)4(Si2O7)2][2] or double that.[5] Kochite is a member of the rosenbuschite group.[6]

Crystallography

Kochite is triclinic with angles intersecting at approximately α 90.192°, β 100.192°, γ 111.551°. This mineral belongs to the space group P1 and is centrosymmetric, i.e. contains a center of symmetry.[7]

It is an anisotropic mineral as the light entering the mineral is split into two rays that vibrate at 90° to each other.[2] It is biaxial, meaning it has two optic axes (lines of symmetry). In plane polarized light, this mineral is colorless to light brown and is pleochroic. As the stage of the microscope is turned from X to Z the color changes from colorless to a pale brownish-yellow.[8] Kochite is also a birefringent mineral, showing bright colors under crossed polarization. Its birefringence is .0340.[8]

Discovery and occurrence

Kochite is found in the alkaline igneous complex of East Greenland and is named after Danish geologist Lauge Koch (1892-1964), a geologist who overturned the previous conception of Greenland's landscapes. It is the titanium – manganese analog of rosenbuschite and occurs in nepheline syenite associated with nepheline, alkali feldspar, and låvenite in the Werner Bjerge alkaline complex along the eastern coast of Greenland.[8]

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. ^ a b c Mindat.org
  3. ^ Webmineral data
  4. ^ Mineralien Atlas
  5. ^ Jambor, J.L.; Roberts, A.C. (January 2004). "New Mineral Names". American Mineralogist. 89 (1): 249–253.
  6. ^ Christiansen, Claes C., Ole Johnsen and Emil Makovicky, Crystal Chemistry of the Rosenbuscite Group, The Canadian Mineralogist, Vol. 41, pp. 1203-1224 (2003)
  7. ^ Mandarino, J.A. (2004) Abstracts of New Mineral Descriptions. The Mineralogy Record, 35, 354-355
  8. ^ a b c Christiansen, C.C., Gault, R.A., Grice, and J.D., Johnsen, O. (2003) Kochite, a new member of the rosenbuschite group from the Werner Bjerge alkaline complex, East Greenland. European Journal of Mineralogy, 15, 551-554 ]

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