metamorphic
Mica Schist with Quartz
Muscovite/Biotite Schist
Hardness: 2.5-4 (mica) to 7 (quartz matrix), Color: Silvery-white to tan/cream, Luster: Pearly to vitreous (reflective flakes), Structure: Foliated with distinct platy minerals, Cleavage: Inherent basal cleavage in the mica flakes.
- Hardness
- 2
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Physical properties
Hardness: 2.5-4 (mica) to 7 (quartz matrix), Color: Silvery-white to tan/cream, Luster: Pearly to vitreous (reflective flakes), Structure: Foliated with distinct platy minerals, Cleavage: Inherent basal cleavage in the mica flakes.
Formation & geological history
Formed from the regional metamorphism of shale or mudstone under intermediate to high pressure and temperature conditions, causing the growth of large, visible mica crystals.
Uses & applications
Used historically as a source for mica in electrical insulation and heat-resistant windows; currently primarily of interest for geological study and as a decorative stone.
Geological facts
The sparkling 'glitter' effect is caused by the alignment of mica minerals (schistosity), which allows the rock to split easily into thin plates. It represents a higher metamorphic grade than slate or phyllite.
Field identification & locations
Identify by looking for 'sparkly' flakes that can be peeled with a fingernail or needle. Found globally in ancient mountain belts and metamorphic terrains like the Appalachians or the Alps.
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