metamorphic
Banded Gneiss
Gneiss (complex metamorphic silicate rock)
Hardness: 6-7 on Mohs scale; Color: alternating dark and light bands of black, grey, and white; Luster: dull to vitreous; Structure: foliated with distinct compositional banding (gneissose banding).
- Hardness
- 6-7 on Mohs scale
- Color
- alternating dark and light bands of black, grey, and white
- Luster
- dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale; Color: alternating dark and light bands of black, grey, and white; Luster: dull to vitreous; Structure: foliated with distinct compositional banding (gneissose banding).
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under intense heat and pressure. This specimen likely dates from the Precambrian or Paleozoic eras.
Uses & applications
Used as decorative crushed stone, dimension stone for buildings, countertops, and often as tumbled pocket stones for collectors.
Geological facts
Gneiss is among the oldest known rocks on Earth, with the Acasta Gneiss in Canada estimated to be over 4 billion years old. The 'zebra' banding is caused by the segregation of minerals into layers.
Field identification & locations
Identified in the field by its distinct parallel 'stripy' bands of different colors and lack of easy cleavage (unlike schist). Commonly found in core areas of continents (shields) and mountain ranges.
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