metamorphic

Garnet-bearing gneiss

Biotite–feldspar gneiss with almandine garnet; quartz likely present

AI-generated identification · may be incorrect

Coarse, strongly foliated rock with pink to reddish feldspar, dark biotite/amphibole, gray quartz, and probable garnet. Hardness is roughly 6–7 overall; vitreous quartz, feldspar cleavage, and dark micaceous layers are typical, with specific gravity about 2.7–3.3.

Identified September 12, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when an older granite or volcanic protolith underwent high-grade regional metamorphism, recrystallizing and segregating minerals into bands. Such rocks commonly formed during Precambrian to Paleozoic mountain-building events.

Uses & applications

Used locally as dimension stone, aggregate, landscaping rock, and building veneer; attractive garnet-bearing pieces are collected but are rarely gem-quality.

Geological facts

The pink grains are likely potassium feldspar, while dark minerals define the foliation; reddish grains may be garnet or weathered feldspar. Gneiss is recognized by compositional banding rather than the more uniform texture of granite.

Field identification & locations

Identify it by alternating light and dark mineral-rich bands, coarse interlocking grains, and mica-rich partings; a hand lens and streak/cleavage tests help confirm minerals. Common in ancient continental shields and metamorphic mountain belts.