metamorphic

Biotite-rich gneiss

Foliated quartzo-feldspathic gneiss with biotite mica

AI-generated identification · may be incorrect

Dark gray to brown, coarse-grained and strongly foliated, with glittering mica-rich bands and lighter quartz/feldspar patches. Typical hardness is about 6–7 overall; mica has perfect basal cleavage, while quartz and feldspar are harder and vitreous. Exact mineral proportions cannot be confirmed from the photograph.

Identified September 1, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed by high-grade metamorphism of granite or sedimentary protoliths, commonly during Precambrian mountain-building; the rock may be hundreds of millions to billions of years old. The reported region near 7.4°S, 24.1°E lies within a broad Precambrian basement province where gneiss is geologically plausible.

Uses & applications

Used locally as building stone, aggregate, road material, dimension stone, and occasionally decorative landscaping rock. Attractive polished pieces have modest collector value.

Geological facts

Gneissic banding records segregation and recrystallization during intense heat and pressure; it is not simply layering deposited by water.

Field identification & locations

Identify it by alternating light and dark mineral bands, visible mica sparkle, coarse grains, and a hard, nonporous texture. Common in ancient continental shields, including central African basement terrains; a fresh broken surface and hand lens would improve confidence.