igneous
Porphyritic Basalt (with Amygdules)
Amygdaloidal Porphyritic Basalt
Hardness (6 on Mohs scale), dark grey/greenish basaltic matrix, white plagioclase or zeolite phenocrysts (amygdules), dull to vitreous luster, fine-grained groundmass with visible crystalline inclusions.
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Physical properties
Hardness (6 on Mohs scale), dark grey/greenish basaltic matrix, white plagioclase or zeolite phenocrysts (amygdules), dull to vitreous luster, fine-grained groundmass with visible crystalline inclusions.
Formation & geological history
Formed through rapid cooling of mafic lava on the Earth's surface. The white spots represent gas bubbles (vesicles) that were later filled with secondary minerals like quartz, calcite, or zeolites through hydrothermal activity.
Uses & applications
Crushed stone for road construction, railroad ballast, building stone, and occasionally used as decorative garden stone.
Geological facts
Basalt is the most common rock in the Earth's crust and makes up most of the ocean floor. The white spots in this specimen are called 'amygdules' from the Greek word for 'almond'.
Field identification & locations
Identify by its dark, heavy fine-grained background speckled with lighter mineral inclusions. Commonly found in volcanic regions such as the Pacific Northwest, Hawaii, or old rift valleys like the Mid-Atlantic region.
