Crystal system Triclinic | Space group P1 | |
Category Sorosilicates
Rosenbuschite group Formula
(repeating unit) (Na,Ca)3Ca2(Mn,Ca)ZrTi[(F,O)4(Si2O7)2] Crystal class Pinacoidal (1)
(same H-M symbol) Unit cell a = 10.03, b = 11.33
c = 7.202 [Å]; α = 90.19°
β = 100.33°, γ = 111.55°; Z = 2 | ||
Kochite is a rare silicate mineral with chemical formula of (Na,Ca)3Ca2(Mn,Ca)ZrTi[(F,O)4(Si2O7)2 or double that. Kochite is a member of the rosenbuschite group.
Contents
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.
Kochite is an anisotropic mineral. The light entering the mineral is split into two rays that vibrate at 90° to each other. 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. Kochite is also a birefringent mineral, showing bright colors under crossed polarization. The birefringence of Kochite is .0340.
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. Kochite is the titanium – manganese 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.