igneous

Granite River Pebble

Granite (composed of Quartz, Feldspar, and Biotite)

Hardness: 6-7 Mohs; Color: Mottled tan (feldspar), grey (quartz), and black (biotite/hornblende); Luster: Vitreous when wet or polished; Crystal structure: Phaneritic (coarse-grained)

Hardness: 6-7 Mohs
Luster: Vitreous when wet or polished

Identified May 31, 2026More igneous →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 6-7 Mohs; Color: Mottled tan (feldspar), grey (quartz), and black (biotite/hornblende); Luster: Vitreous when wet or polished; Crystal structure: Phaneritic (coarse-grained)

Formation & geological history

Formed from the slow cooling of silica-rich magma deep underground (plutonic). This specimen appears water-worn, smoothed by transport in a river or coastal environment over thousands of years.

Uses & applications

Used in construction, countertops, monuments, and as decorative landscaping stone. Polished river pebbles are common in home decor and aquariums.

Geological facts

Granite is the primary component of the Earth's continental crust. The specific color of this specimen suggests a high concentration of orthoclase feldspar giving it the yellowish-tan tint.

Field identification & locations

Identify in the field by its speckled 'salt and pepper' appearance and extreme hardness (it will scratch glass). Commonly found in mountainous regions or riverbeds downstream from crystalline basement rocks.

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

Dalmatian Jasper

Aplite with Arfvedsonite inclusions

igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral