igneous
Quartz-rich Diorite
Diorite (Phaneritic intermediate igneous rock)
Hardness: 6-7 Mohs; Color: Salt and pepper (black and white) with clear to milky quartz; Luster: Vitreous to dull; Crystal structure: Phaneritic (visible crystals); Cleavage: Prominent in feldspar, absent in quartz.
- Hardness
- 6-7 Mohs
- Color
- Salt and pepper (black and white) with clear to milky quartz
- Luster
- Vitreous to dull
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Salt and pepper (black and white) with clear to milky quartz; Luster: Vitreous to dull; Crystal structure: Phaneritic (visible crystals); Cleavage: Prominent in feldspar, absent in quartz.
Formation & geological history
Formed through the slow cooling of magma deep beneath the Earth's surface (plutonic). This specimen shows a contact zone between a quartz vein and the host diorite matrix.
Uses & applications
Commonly used as crushed stone for road construction, building foundations, and occasionally as decorative dimension stone (granite-like) in countertops.
Geological facts
Diorite is often called 'Black Granite' in the commercial stone trade, though it contains less silica than true granite. It was famously used by ancient Egyptians for hard-stone sculptures.
Field identification & locations
Identified by its phaneritic texture and lack of high quartz content compared to granite. In the field, look for a speckled appearance where dark minerals (biotite/hornblende) are roughly equal to light minerals (plagioclase).
