igneous
Orbicular basalt (amygdaloidal basalt)
Basalt, commonly with iron-oxide–stained amygdules; matrix chiefly plagioclase, pyroxene, and often olivine
AI-generated identification · may be incorrectFine-grained, dark gray to black, matte to subtly vitreous, with reddish-orange rounded inclusions likely vesicles filled by iron oxides, zeolites, or silica. Hardness about 5–6, no visible cleavage, dense, and typically specific gravity 2.8–3.1.
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Physical properties
Fine-grained, dark gray to black, matte to subtly vitreous, with reddish-orange rounded inclusions likely vesicles filled by iron oxides, zeolites, or silica. Hardness about 5–6, no visible cleavage, dense, and typically specific gravity 2.8–3.1.
Formation & geological history
An extrusive volcanic rock formed when basaltic lava cooled rapidly at or near Earth’s surface, with gas bubbles later filled by secondary minerals. Individual specimens may range from modern volcanic settings to ancient basalt flows of Precambrian or younger age.
Uses & applications
Used as aggregate, riprap, paving stone, and decorative rock; attractive polished pieces are collected as lapidary specimens. This small tumbled specimen has modest commercial value.
Geological facts
The circular spots are amygdules or altered vesicles rather than true crystals, and their orange-red color commonly reflects hematite or iron-rich alteration. The specimen may also be marketed informally as “poppy jasper,” though that trade name is not necessarily mineralogically precise.
Field identification & locations
Identify it by its black fine-grained basaltic matrix, rounded contrasting spots, high density, and lack of layering or visible large crystals; a steel file should scratch it. Common sources include volcanic provinces in India, the western United States, Mexico, and other basalt-rich regions.
