igneous
Basalt (River-worn Specimen)
Extrusive Mafic Igneous Rock
Hardness: 6 (Mohs scale); Color: Dark grey to charcoal grey; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to charcoal grey
- Luster
- Dull/Earthy
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to charcoal grey; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This particular specimen shows rounded edges indicating water erosion in a river or coastal environment, a process occurring over hundreds to thousands of years.
Uses & applications
Commonly used as crushed stone for road base, concrete aggregate, railroad ballast, and high-quality asphalt. In specialized forms, it is used for stone wool insulation or in dimensional stone for landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify by its heavy weight (high density), dark color, and lack of visible individual crystals without a lens. Often found in volcanic regions or in riverbeds downstream from volcanic sources. Collectors look for unique wear patterns or vesicles (gas bubbles), though this specimen is solid and water-worn.
More like this
Other igneous specimens
Blue Apatite
Fluorapatite (Ca5(PO4)3F)
mineral
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.
Igneous
Magnetite
Iron(II,III) oxide (Fe3O4)
mineral
Blue Apatite
Apatite (Group), Ca5(PO4)3(F,Cl,OH)
mineral
Sodalite
Sodalite - Na8(Al6Si6O24)Cl2
mineral
Magnetite
Magnetite (Fe3O4)
mineral