Opal-CT (Lussatite)
Image: <a href="//commons.wikimedia.org/wiki/User:Archaeodontosaurus" title="User:Archaeodontosaurus">Didier Descouens</a> (CC BY-SA 4.0)
Mineral NameOpal-CT (Lussatite)
Chemical FormulaSiO2·nH2O
Mohs Hardness5.5
Crystal Systemamorphous
Lustervitreous
Streak Colorwhite
Cleavagenone
Fractureconchoidal
Specific Gravity2.1
Colorswhite, light blue, grey, brown
Transparencytranslucent
Type LocalityMine des Rois, Dallet, Pont-du-Château, Puy-de-Dôme, Auvergne, France
Mineral GroupSilicates (Mineraloid)
Usescollector, minor ornamental
Associated Mineralschalcedony, zeolites, volcanic rock matrix
Rarityuncommon
Description
This specimen features botryoidal to globular aggregates of whitish to light bluish-grey Opal-CT (Lussatite) on a dark, rough, and somewhat porous matrix.
Geological Context
Opal-CT, also known as lussatite, forms from the precipitation of silica-rich solutions, often found in altered volcanic rocks, hot spring deposits, or sedimentary environments.
