igneous
Amygdaloidal Basalt
Basalt with secondary mineral infilling
Hardness: 5-6 (matrix); Color: Dark grey to dull green with white/buff spots; Luster: Dull to earthy; Structure: Vesicular/Amygdaloidal; Specific Gravity: 2.8-3.0
- Hardness
- 5-6 (matrix)
- Color
- Dark grey to dull green with white/buff spots
- Luster
- Dull to earthy
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5-6 (matrix); Color: Dark grey to dull green with white/buff spots; Luster: Dull to earthy; Structure: Vesicular/Amygdaloidal; Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava. The 'spots' are amyg dules, which formed when gas bubbles (vesicles) in the cooling lava were later filled with secondary minerals like quartz, calcite, or zeolites through groundwater infiltration.
Uses & applications
Primarily used as crushed stone for aggregate in construction, road base, and concrete. Interesting specimens are used for educational purposes and geological collecting.
Geological facts
Amygdaloidal textures are common in ancient volcanic flows, such as those found in the Lake Superior region of North America, where these pockets can sometimes contain native copper or semi-precious gemstones.
Field identification & locations
Identify by the dark, fine-grained volcanic matrix containing rounded, light-colored mineral 'pockets.' Commonly found in volcanic terrains and glacial till in volcanic regions.
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