metamorphic

Granite Gneiss

Gneiss (High-grade Regional Metamorphic Rock)

AI-generated identification · may be incorrect

Hardness: 6-7 on Mohs scale; Color: Mottled black, pink, and white/grey; Luster: Dull to vitreous when wet; Structure: Foliated or banded with interlocking mineral grains; Specific Gravity: 2.6-2.9.

Hardness: 6-7 on Mohs scale
Color: Mottled black, pink, and white/grey
Luster: Dull to vitreous when wet

Identified June 28, 2026More metamorphic →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: Mottled black, pink, and white/grey; Luster: Dull to vitreous when wet; Structure: Foliated or banded with interlocking mineral grains; Specific Gravity: 2.6-2.9.

Formation & geological history

Formed through the high-grade regional metamorphism of a granitic protolith under intense heat and pressure, causing segregation of mafic and felsic minerals.

Uses & applications

Used primarily in construction for crushed stone or decorative landscaping. High-quality specimens are used for countertops and architectural cladding.

Geological facts

Gneiss is one of the oldest rock types on Earth; the Acasta Gneiss in Canada is approximately 4 billion years old.

Field identification & locations

Identify in the field by looking for 'gneissose banding' or visible segregation of dark (biotite/hornblende) and light (quartz/feldspar) minerals. Found in crystalline basement terrains and mountainous regions.