igneous

Granodiorite Pebble

Granodiorite

Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (mottled gray, white, and black). Luster: Dull to vitreous. Crystal structure: Phaneritic (visible crystals). Cleavage: Varies by mineral constituent. Specific gravity: 2.6-2.7.

Hardness: 6-7 on Mohs scale
Color: Salt-and-pepper (mottled gray, white, and black)
Luster: Dull to vitreous

Identified April 6, 2026More igneous →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through the slow cooling of silica-rich magma beneath the Earth's surface (intrusive). This specific specimen is a water-worn pebble, likely eroded from a pluton and rounded by river or glacial action.

Uses & applications

Used primarily in construction as crushed stone, road base, and occasionally as decorative gravel or 'river rock' in landscaping.

Geological facts

Granodiorite is the intermediate rock between granite and diorite. The famous Rosetta Stone was carved from a slab of granodiorite, not basalt as originally thought.

Field identification & locations

Identify in the field by its phaneritic texture and the presence of more plagioclase feldspar than orthoclase. Commonly found in batholiths and mountain roots. For collectors, look for the distinct 'salt and pepper' appearance in rounded river stones.

Other igneous specimens

See all

Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous