Kochite

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Kochite
General
Category Sorosilicates
Rosenbuschite group
Formula
(repeating unit)
(Na,Ca)3Ca2(Mn,Ca)ZrTi[(F,O)4(Si2O7)2]
Crystal system Triclinic
Crystal class Pinacoidal (1)
(same H-M symbol)
Space group P1
Unit cell a = 10.03, b = 11.33
c = 7.202 [Å]; α = 90.19°
β = 100.33°, γ = 111.55°; Z = 2
Identification
Color Colorless to light brown
Crystal habit Acicular to lath-shaped prismatic crystals
Cleavage {100} perfect
Fracture Uneven
Tenacity Brittle
Mohs scale hardness 5
Luster Vitreous
Streak White
Diaphaneity Transparent
Specific gravity 3.32
Optical properties Biaxial (+)
Refractive index nα=1.684, nβ=1.695, nγ=1.718
Birefringence 0.0340
Pleochroism weak, colorless to pale brownish-yellow
References [1][2][3]

Kochite is a rare silicate mineral with chemical formula of (Na,Ca)3Ca2(Mn,Ca)ZrTi[(F,O)4(Si2O7)2[1] or double that.[4] Kochite is a member of the rosenbuschite group.[5]

Crystallography[edit]

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.[6]

Kochite is an anisotropic mineral. The light entering the mineral is split into two rays that vibrate at 90° to each other.[1] Kochite 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.[7] Kochite is also a birefringent mineral, showing bright colors under crossed polarization. The birefringence of Kochite is .0340.[7]

Discovery and occurrence[edit]

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. Kochite is the titaniummanganese analog of rosenbuschite. It occurs in nepheline syenite associated with nepheline, alkali feldspar, and låvenite in the Werner Bjerge alkaline complex along the eastern coast of Greenland.[7]

References[edit]

  1. ^ a b c Mindat.org
  2. ^ Webmineral data
  3. ^ Mineralien Atlas
  4. ^ Jambor, J.L., Roberts, A.C. (2004) New Mineral Names. American Mineralogist, 89, 249-253
  5. ^ Christiansen, Claes C., Ole Johnsen and Emil Makovicky, Crystal Chemistry of the Rosenbuscite Group, The Canadian Mineralogist, Vol. 41, pp. 1203-1224 (2003)
  6. ^ Mandarino, J.A. (2004) Abstracts of New Mineral Descriptions. The Mineralogy Record, 35, 354-355
  7. ^ 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 ]