metamorphic
Gneiss
Metamorphic Gneiss
Hardness 6-7 on Mohs scale, earthy to vitreous luster, banded or foliated texture, gray to reddish-brown coloration due to iron-oxide staining, composed mainly of quartz and feldspar
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Physical properties
Hardness 6-7 on Mohs scale, earthy to vitreous luster, banded or foliated texture, gray to reddish-brown coloration due to iron-oxide staining, composed mainly of quartz and feldspar
Formation & geological history
Formed under high-grade regional metamorphism subjecting original igneous or sedimentary rocks to intense heat and pressure deep within Earth's crust
Uses & applications
Used as crushed stone in road construction, building facing, landscaping, and decorative stone work
Geological facts
Gneiss is one of the oldest rock types on Earth; the Acasta Gneiss in Canada is dated to over 4 billion years old
Field identification & locations
Identified by distinct alternating light and dark mineral bands and coarse texture. Commonly found in mountainous regions and exposed continental shields worldwide
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