igneous
Amygdaloidal Basalt with Agate/Quartz Infill
Basalt with Secondary Silicate Mineralization (SiO2)
Hardness: 6-7. Color: Reddish-brown host rock with white to grey crystalline infill. Luster: Dull/earthy (matrix) to vitreous (centers). Structure: Aphanitic matrix with amygdaloidal vesicles.
- Hardness
- 6-7
- Luster
- Dull/earthy (matrix) to vitreous (centers)
Identified More igneous →
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Physical properties
Hardness: 6-7. Color: Reddish-brown host rock with white to grey crystalline infill. Luster: Dull/earthy (matrix) to vitreous (centers). Structure: Aphanitic matrix with amygdaloidal vesicles.
Formation & geological history
Formed from cooling basaltic lava where gas bubbles (vesicles) were later filled by silica-rich hydrothermal fluids. The reddish color indicates high iron content that has oxidized. Common in areas like the Lake Superior region.
Uses & applications
Primarily collected as lapidary material or display specimens. Larger deposits are used for crushed stone in construction.
Geological facts
This specimen is often called a 'Laker' or 'Lake Superior Agate' in its early form. The white ring inside the rock represents the wall of a gas bubble that existed millions of years ago when the lava was molten.
Field identification & locations
Look for rounded basalt rocks with distinct white or colorful rings on the surface. Commonly found on beaches or in glacial till in the Northern United States and volcanic regions globally.
