igneous
Diorite (Spotted)
Plutonic Igneous Rock (Diorite)
Hardness: 6-7 on Mohs scale. Color: Black and white (salt and pepper). Luster: Dull to sub-vitreous. Structure: Phaneritic (coarse-grained) with large crystals of plagioclase feldspar and darker minerals like hornblende or biotite.
- Hardness
- 6-7 on Mohs scale
- Color
- Black and white (salt and pepper)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Black and white (salt and pepper). Luster: Dull to sub-vitreous. Structure: Phaneritic (coarse-grained) with large crystals of plagioclase feldspar and darker minerals like hornblende or biotite.
Formation & geological history
Formed through the slow cooling of magma beneath the Earth's surface in volcanic arcs or mountain-building regions. Common in the Baltic Shield area around St. Petersburg, often transported as glacial erratics from Finland/Karelia.
Uses & applications
Used primarily as a dimension stone for construction, paving, and monuments. When polished, it is sometimes used for floor tiles or kitchen countertops.
Geological facts
Diorite is often called 'Black Granite' in the commercial stone trade, though it lacks the quartz content required to be a true granite. It was used by Ancient Egyptians for sculptures due to its extreme hardness.
Field identification & locations
Identify in the field by its distinctive 'Dalmatian' or 'Salt and Pepper' appearance without the visible quartz grains found in granite. In the Leningrad region, look for these in glacial deposits and riverbeds.
