Cookeite
Image: Didier Descouens (CC BY-SA 4.0)
Mineral NameCookeite
Chemical Formula(Li,Al)Al₄(Si₃Al)O₁₀(OH)₈
Mohs Hardness2.5
Crystal Systemmonoclinic
Lusterpearly
Streak Colorwhite
Cleavageperfect on {001}
Fractureuneven
Specific Gravity2.69
Colorswhite, pink, yellow, green, brown, colorless
Transparencytransparent
Type LocalityMt Mica Quarry, Paris, Oxford Co., Maine, USA
Mineral Groupphyllosilicates
Usescollector
Associated Mineralsquartz, tourmaline, lepidolite, albite, beryl, spodumene
Rarityuncommon
Description
The image shows a reddish-brown, granular to scaly mass of cookeite, with small, clear, prismatic quartz crystals embedded within it and growing on a larger, translucent white quartz crystal.
Geological Context
Cookeite is a lithium-aluminum chlorite mineral typically found in lithium-rich granitic pegmatites, often as an alteration product of other lithium minerals or as a late-stage hydrothermal mineral.
