igneous
Amygdaloidal Basalt with Quartz
Basalt (SiO2 inclusion)
Hardness: 6-7 (basalt matrix), 7 (quartz); Color: Dull greenish-grey matrix with white/translucent crystal pockets; Luster: Earthy to vitreous; Structure: Vesicular/Amygdaloidal; Specific Gravity: 2.8-3.0
- Hardness
- 6-7 (basalt matrix), 7 (quartz)
- Luster
- Earthy to vitreous
Identified More igneous →
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Physical properties
Hardness: 6-7 (basalt matrix), 7 (quartz); Color: Dull greenish-grey matrix with white/translucent crystal pockets; Luster: Earthy to vitreous; Structure: Vesicular/Amygdaloidal; Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the cooling of magnesium-rich and iron-rich lava. The holes (vesicles) were created by gas bubbles, which later filled with secondary minerals like quartz or calcite via groundwater infiltration.
Uses & applications
Used primarily as crushed stone for aggregate in construction, road base, and railroad ballast. Decorative specimens are popular among amateur geologists.
Geological facts
The word 'amygdule' comes from the Greek word for 'almond', referring to the almond-shaped mineral fillings found in the volcanic gas bubbles. This specimen appears water-worn, likely from a river or beach.
Field identification & locations
Identify in the field by its heavy weight, dark fine-grained matrix, and 'pockets' of different colored minerals. Commonly found in volcanic regions such as the Lake Superior basin or the Deccan Traps.
