igneous
Granite (or Gneiss/Diorite Pebble)
Granite / Granodiorite
Hardness: 6-7 on Mohs scale. Color: Speckled grey, white, and black with visible quartz and feldspar grains. Luster: Dull to vitreous on crystalline faces. Texture: Medium to coarse-grained phaneritic texture. Specific gravity: ~2.63 - 2.75.
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to vitreous on crystalline faces
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Speckled grey, white, and black with visible quartz and feldspar grains. Luster: Dull to vitreous on crystalline faces. Texture: Medium to coarse-grained phaneritic texture. Specific gravity: ~2.63 - 2.75.
Formation & geological history
Formed from the slow cooling and crystallization of magma deep beneath the Earth's surface (plutonic formation). Later exposed by erosion and rounded by water transport in a river bed or glacial environment.
Uses & applications
Widely used in construction, dimension stone, countertops, paving, aggregate, and as decorative landscape pebbles.
Geological facts
Granite forms the core of most continental crusts. The speckling is due to individual mineral grains of quartz, plagioclase, orthoclase feldspar, and biotite mica or hornblende.
Field identification & locations
Identify by its speckled 'salt-and-pepper' appearance and hard interlocking quartz and feldspar crystals. Commonly found in riverbeds, gravel pits, and mountainous regions globally.
