metamorphic
Gneiss
Gneiss (High-grade metamorphic rock)
Hardness: 6-7 on Mohs scale; Color: typically banded grey, pink, or brownish; Luster: vitreous to dull; Crystal structure: crystalline with visible mineral bands; Cleavage: poor; Specific gravity: approx. 2.6-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- typically banded grey, pink, or brownish
- Luster
- vitreous to dull
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Physical properties
Hardness: 6-7 on Mohs scale; Color: typically banded grey, pink, or brownish; Luster: vitreous to dull; Crystal structure: crystalline with visible mineral bands; Cleavage: poor; Specific gravity: approx. 2.6-3.0.
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under intense heat and pressure, often found in the cores of mountains or ancient shield areas.
Uses & applications
Used as a dimension stone in construction, flooring, exterior cladding, and as decorative crushed stone in landscaping and road bases.
Geological facts
Gneiss features a characteristic texture called ‘gneissic banding,’ where minerals separate into distinct light and dark layers. Some of the oldest known rocks on Earth are Acasta Gneiss, dated to over 4 billion years old.
Field identification & locations
Identify by looking for distinct foliation or layering of minerals (banding). It is commonly found in mountain ranges like the Appalachians or Himalayas. For collectors, it represents the power of tectonic tectonic forces.
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