Mineral species of the silicate group and the phyllosilicate subgroup, part of the chlorite family.
Main article: Chlorite group
Cookeite
Cookeite on quartz, Paris, Maine, topotype deposit
General
Category
IX
Formula (repeating unit)
LiAl 4(Si 3Al)O 10(OH) 8
Strunz classification
09.EC.55
Dana classification
71.04.01.02
Crystal system
monoclinic
Crystal class
prismatic; C2 or Cc
Identification
Color
white, green, brown, golden, pink
Twinning
around [310]
Cleavage
perfect over {001}
Fracture
flexible
Tenacity
2,5
Luster
pearly; silky
Density
from 2.58 to 2.69
Refractive index
α = 1,572–1,576, β = 1,579–1,584, γ = 1,589–1,6
Birefringence
biaxial (+), 0,0170–0,0240 2V = 35 to 60°
Pleochroism
x = y: pale green to pink, z: colorless to pale yellow
Ultraviolet fluorescence
cream yellow (SW)
Cookeite is a mineral species of the silicate group and the phyllosilicate subgroup, part of the chlorite family, with the formula LiAl4(Si3Al)O10(OH)8.[1] This soft, low-density mineral of variable color has a crystalline structure made up of alternating layers LiAl2(OH)6 and Al2O4(OH)2Si8O12 having several polytypes. Cookeite is often found as a product of hydrothermal alteration of silicates in pegmatites. It forms at relatively low temperatures (below 200°C) and variable pressures.
^P. Černý, "Compositional variations in cookeite", Can. Mineral., vol. 10, no 4, December 1970, p. 636–647 (ISSN 0008-4476, read online).
Cookeite is a mineral species of the silicate group and the phyllosilicate subgroup, part of the chlorite family, with the formula LiAl4(Si3Al)O10(OH)8...
with source. It often occurs intermixed with chlorite, muscovite, illite, cookeite, and kaolinite. Montmorillonite can be concentrated and transformed within...
List of minerals List of minerals named after people Portlandite, Ca(OH)2 Cookeite, LiAl4(Si3Al)O10(OH)8 Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols"...
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