igneous
Granodiorite Pebble
Granodiorite
Hardness: 6-7 on Mohs scale. Color: Salt and pepper (mottled grey, white, and black). Luster: Dull/Matte (tumbled). Crystal Structure: Phaneritic (medium-grained visible crystals). Cleavage: Varies by mineral constituent. Specific Gravity: 2.6-2.7.
- Hardness
- 6-7 on Mohs scale
- Color
- Salt and pepper (mottled grey, white, and black)
- Luster
- Dull/Matte (tumbled)
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Salt and pepper (mottled grey, white, and black). Luster: Dull/Matte (tumbled). Crystal Structure: Phaneritic (medium-grained visible crystals). Cleavage: Varies by mineral constituent. Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the slow cooling of silica-rich magma deep underground (intrusive). This specific specimen has been tumbled and rounded by water action, likely in a river or beach environment. Age can range from millions to billions of years depending on the batholith of origin.
Uses & applications
Primary use is in construction (crushed stone, road base) and architecture (countertops, curbing). Small water-worn pebbles are used decoratively in landscaping or aquariums.
Geological facts
Granodiorite is intermediate between granite and diorite. The famous Rosetta Stone was carved into a slab of granodiorite, not basalt as was originally thought.
Field identification & locations
Identify by its 'salt and pepper' appearance and visible crystals. It contains more plagioclase feldspar than orthoclase feldspar compared to true granite. Commonly found in mountainous regions or glacial till and riverbeds downstream from mountain ranges.
