igneous
Granodiorite Pebble
Granodiorite
Hardness: 6-7 (Mohs); Color: Mottled salt-and-pepper (white, grey, tan, and black); Luster: Dull to vitreous; Crystal structure: Phaneritic (medium-grained crystalline); Specific Gravity: 2.6-2.7
- Hardness
- 6-7 (Mohs)
- Color
- Mottled salt-and-pepper (white, grey, tan, and black)
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 (Mohs); Color: Mottled salt-and-pepper (white, grey, tan, and black); Luster: Dull to vitreous; Crystal structure: Phaneritic (medium-grained crystalline); Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground (intrusive). This typically occurs in continental volcanic arcs and orogenic belts. Most specimens range from Mesozoic to Cenozoic eras.
Uses & applications
Commonly used as crushed stone for road base, concrete aggregate, and construction. Large deposits are used for architectural cladding or countertops.
Geological facts
Granodiorite is the intermediate rock between granite and diorite. The famous Rosetta Stone was carved from a slab of granodiorite.
Field identification & locations
Identify by its 'salt and pepper' appearance with more plagioclase feldspar than orthoclase. It is commonly found in riverbeds or glacial tills as rounded pebbles like this one. Tips: Look for interlocking crystals and a lack of layering.
