igneous
Vesicular basalt with zeolite or calcite amygdules
Basalt; commonly plagioclase–clinopyroxene–olivine, with secondary zeolite/calcite fillings
AI-generated identification · may be incorrectDark gray, fine-grained volcanic rock with abundant gas vesicles and white crystalline cavities; typically dull to slightly glassy, hardness about 5–6, no obvious cleavage, and specific gravity roughly 2.7–3.0. The metallic-looking patches may be reflective zeolite, calcite, or weathered sulfide/iron-oxide surfaces.
Identified More igneous →
Explore Vesicular basalt with zeolite or calcite amygdules in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray, fine-grained volcanic rock with abundant gas vesicles and white crystalline cavities; typically dull to slightly glassy, hardness about 5–6, no obvious cleavage, and specific gravity roughly 2.7–3.0. The metallic-looking patches may be reflective zeolite, calcite, or weathered sulfide/iron-oxide surfaces.
Formation & geological history
Formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles; later groundwater deposited minerals in some cavities. Basalt ranges from Precambrian to modern age and occurs in volcanic provinces, lava flows, and oceanic crust.
Uses & applications
Used as crushed aggregate, road stone, riprap, and building material; attractive amygdaloidal pieces are collected or cut for display. Value is usually modest unless the cavity minerals are unusually well crystallized.
Geological facts
The specimen’s irregular holes are vesicles, while mineral-filled holes are amygdules. Common sources include India’s Deccan Traps, Oregon, Washington, Iceland, Mexico, and many oceanic volcanic islands.
Field identification & locations
Identify it by its dark volcanic matrix, high density, abundant rounded vesicles, and white secondary minerals; a streak, acid, and hardness test can distinguish calcite from zeolite. Estimated value: $5–$30 for a typical hand specimen, potentially $50–$150 for exceptional mineral-filled examples.
