igneous
Vesicular Basalt (Scoria)
Mafic Igneous Rock (primarily Plagioclase Feldspar and Pyroxene)
Hardness: 5-6 Mohs; Color: Black, dark gray, or reddish-brown; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) with vesicles; Specific Gravity: 2.8-3.0
- Hardness
- 5-6 Mohs
- Color
- Black, dark gray, or reddish-brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 Mohs; Color: Black, dark gray, or reddish-brown; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) with vesicles; Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (magma) at the Earth's surface. The pits or 'pores' are called vesicles, which were formed by gas bubbles trapped in the cooling lava. Most basalt is relatively young geologically, found in oceanic crust and volcanic hotspots.
Uses & applications
Used primarily in landscaping (lava rocks), as an aggregate in road construction and concrete, in high-temperature insulation (stone wool), and occasionally in BBQ grills for heat retention.
Geological facts
Basalt is the most common rock type in Earth's crust and also makes up most of the surface of the Moon and Mars. On Earth, it forms the giant 'Giant's Causeway' in Ireland and the 'Devil's Postpile' in California.
Field identification & locations
Identify by its dark color, heavy weight (relative to same-sized rocks), and characteristic small holes or bubbles. It is frequently found near volcanic regions, rift valleys, and oceanic ridges.
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Dark Igneous Rock (Likely Basalt or Diabase)
Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.
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