Cookeite
Image: Robert M. Lavinsky (CC BY-SA 3.0)
Mineral NameCookeite
Chemical Formula(Li,Al)Al4(Si3Al)O10(OH)8
Mohs Hardness2.5
Crystal Systemmonoclinic
Lusterpearly
Streak Colorwhite
Cleavageperfect on {001}
Fractureuneven
Specific Gravity2.67
Colorswhite, pink, pale green, yellowish, colorless
Transparencytransparent
Type LocalityBarra de Salinas district, Barra de Salinas, Coronel Murta, Jequitinhonha valley, Minas Gerais, Southeast Region, Brazil
Mineral GroupSilicates
Usescollector, gemstone
Associated Mineralstourmaline, quartz, lepidolite, albite, spodumene, beryl
Rarityuncommon
Description
This image displays a pale green, translucent specimen of Cookeite, likely a cut or polished piece, exhibiting a distinct pearly to vitreous luster and a platy or micaceous habit.
Geological Context
Cookeite is a lithium-bearing chlorite group mineral that typically forms in lithium-rich granitic pegmatites, often as a hydrothermal alteration product of other lithium minerals like spodumene or lepidolite, or in some metamorphic rocks.
