igneous
Rounded porphyritic volcanic pebble
Likely andesite porphyry (identification from the photo is approximate)
AI-generated identification · may be incorrectFine-grained, olive-gray matrix with scattered pale feldspar-like crystals and dark mineral grains; rounded by transport. Likely hardness about 6 on Mohs scale, with no obvious cleavage; specific gravity roughly 2.5–2.8.
Identified More igneous →
Explore Rounded porphyritic volcanic pebble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Fine-grained, olive-gray matrix with scattered pale feldspar-like crystals and dark mineral grains; rounded by transport. Likely hardness about 6 on Mohs scale, with no obvious cleavage; specific gravity roughly 2.5–2.8.
Formation & geological history
Probably cooled from volcanic lava, then weathered and rounded in a stream or on a beach. Andesitic rocks are common in the active volcanic belt of central Chile; the pebble’s age cannot be determined from the image.
Uses & applications
As a small pebble it has little industrial value; similar andesite is used as crushed aggregate and building stone. This specimen is mainly of interest to collectors.
Geological facts
Its speckled appearance may reflect larger crystals embedded in a finer volcanic groundmass, a texture called porphyritic.
Field identification & locations
A hand lens can reveal crystals, and a fresh broken surface would help distinguish andesite from other volcanic rocks. The reported central-Chile location is geologically plausible; a rounded pebble could have been transported from its source.
