igneous
Mottled gabbro or diorite pebble
Coarse-grained mafic/intermediate intrusive rock; chiefly plagioclase feldspar plus pyroxene, with possible amphibole or biotite
AI-generated identification · may be incorrectDark gray, speckled, massive and crystalline with a granular texture; typical Mohs hardness 6–7, vitreous to dull luster, no cleavage as a whole, and specific gravity about 2.7–3.1. The rounded shape indicates natural abrasion or tumbling.
Identified More igneous →
Explore Mottled gabbro or diorite pebble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray, speckled, massive and crystalline with a granular texture; typical Mohs hardness 6–7, vitreous to dull luster, no cleavage as a whole, and specific gravity about 2.7–3.1. The rounded shape indicates natural abrasion or tumbling.
Formation & geological history
Formed when magma cooled slowly deep underground, allowing visible interlocking crystals to grow; likely Precambrian to younger, depending on source. Common in plutonic bodies and glacial or stream gravels.
Uses & applications
Used as crushed aggregate, dimension stone, paving and landscaping material; attractive polished pieces may be used as bookends or lapidary specimens, but it is generally not a gemstone.
Geological facts
The image shows a dark, strongly mottled rock, but exact identification requires a fresh surface, grain-size inspection, and mineral tests. More blue-gray, feldspar-rich material favors diorite; darker, pyroxene-rich material favors gabbro.
Field identification & locations
Commonly found in igneous terrains, mountain regions, riverbeds and glacial deposits. A streak test, hardness test, acid test, and close examination for black pyroxene versus lighter feldspar can refine identification.
