Greenalite - Encyclopedia
Class : Silicates
Subclass : Phyllosilicates
Crystal system : Monoclinic
Chemistry : Fe2-3Si2O5(OH)4
Rarity : Rare
Greenalite is a rare mineral from the kaolinite group. It is a primary phyllosilicate that is mainly found in banded iron deposits (BIFs), notably accompanying stilpnomelane, siderite, pyrite and chamosite. Greenalite also forms by diagenesis in tropical sediments. It was named so in reference to its green color. Greenalite is usually massive or in the form of rounded fibrous granules of pale yellow-green to dark green, millimeter-sized, which frequently causes confusion with glauconite. It is a mineral which alters into iron oxides.
Main photo : Gratonite from Excelsior Mine, Cerro de Pasco, Pasco province, Pasco, Peru © Rob Lavinsky
Greenalite in the World
Twinning
No twins known for this mineral species.
Fakes and treatments
No fakes recorded for this mineral species but possible confusion with glauconite.
Hardness : 2.5
Density : 2.85 to 3.15
Fracture : Micaceous
Streak : Gray-green
TP : Translucent
RI : 1.650 to 1.675
Birefringence : 0.024
Optical character : Biaxial +
Pleochroism : Visible
Fluorescence : None
Solubility : -
Magnetism : ParamagneticRadioactivity : None