metamorphic
Banded Gneiss
Gneiss (High-grade Regional Metamorphic Rock)
Hardness: 6-7 on Mohs scale; Color: Gray, tan, and reddish-brown bands; Luster: Dull to pearly; Crystal structure: Coarse-grained foliated; Cleavage: Poorly defined (breaks irregularly); Specific Gravity: 2.6-2.9.
- Hardness
- 6-7 on Mohs scale
- Color
- Gray, tan, and reddish-brown bands
- Luster
- Dull to pearly
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Gray, tan, and reddish-brown bands; Luster: Dull to pearly; Crystal structure: Coarse-grained foliated; Cleavage: Poorly defined (breaks irregularly); Specific Gravity: 2.6-2.9.
Formation & geological history
Formed through high-pressure, high-temperature regional metamorphism of pre-existing igneous or sedimentary rocks. This specimen shows distinct gneissic banding where minerals have segregated into layers during tectonic deformation.
Uses & applications
Commonly used in construction as crushed stone or 'dimension stone' for flooring, countertops, and grave markers; also used for landscaping and as an educational geological specimen.
Geological facts
Gneiss is one of the oldest known rock types on Earth, with some specimens in Northern Canada dated to over 4 billion years old. The banding often represents the flow of minerals under intense heat and pressure.
Field identification & locations
Identified in the field by its distinct alternating 'zebra-like' bands of light and dark minerals. Look for it in mountain ranges or deep-crustal exposures. It lacks the distinct cleavage planes found in schist.
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