metamorphic
Banded Gneiss
Gneiss (High-grade regional metamorphic rock)
Hardness: 6-7 on Mohs scale. Color: Alternating dark (mafic) and light (felsic) bands. Luster: Dull to vitreous. Structure: Foliated with distinct 'gneissic banding.' Cleavage: Poor, usually breaks along uneven surfaces. Specific gravity: 2.6-2.9.
- Hardness
- 6-7 on Mohs scale
- Color
- Alternating dark (mafic) and light (felsic) bands
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Alternating dark (mafic) and light (felsic) bands. Luster: Dull to vitreous. Structure: Foliated with distinct 'gneissic banding.' Cleavage: Poor, usually breaks along uneven surfaces. Specific gravity: 2.6-2.9.
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks at extreme temperatures (above 600°C) and pressures. This specimen displays a heart-like shape likely due to natural fluvial or coastal erosion.
Uses & applications
Used primarily in construction as crushed stone for road bases or as ornamental building stone (countertops, flooring). Also cherished by rockhounds when found in unique weathered shapes like this heart.
Geological facts
Gneiss is among the oldest known rocks on Earth; the Acasta Gneiss in Canada is approximately 4.03 billion years old. The 'banding' occurs because minerals segregate into layers during intense pressure without melting completely.
Field identification & locations
Identify in the field by looking for 'zebra stripes' or distinct mineral layering in hard crystalline rock. Commonly found in the roots of ancient mountain ranges or glacial till. For collectors, heart-shaped natural stones are prized as 'curio' specimens.
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