metamorphic or igneous

Quartz River Pebble with Algae

Silicon Dioxide (SiO2) with organic biofilm

Hardness: 7 on Mohs scale; Color: Creamy white with green surface organic matter; Luster: Vitreous to waxy; Structure: Hexagonal (cryptocrystalline); Cleavage: None (conchoidal fracture).

Hardness: 7 on Mohs scale
Color: Creamy white with green surface organic matter
Luster: Vitreous to waxy

Identified June 19, 2026More metamorphic or igneous →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 7 on Mohs scale; Color: Creamy white with green surface organic matter; Luster: Vitreous to waxy; Structure: Hexagonal (cryptocrystalline); Cleavage: None (conchoidal fracture).

Formation & geological history

Formed from hydrothermal veins or metamorphic activity, then eroded and smoothed by high-energy water transport (river or beach action) over thousands of years.

Uses & applications

Commonly used in landscaping, decorative ground cover, aquarium gravel, and as a source of industrial silica if found in large deposits.

Geological facts

This specimen appears to be 'green' not due to mineral content, but due to chlorophyta (green algae) growing on its wet surface. Quartz is one of the most chemically resistant minerals on Earth's surface.

Field identification & locations

Field identification involves checking for hardness (won't scratch with a knife) and the rounded 'tumbled' shape. Often found in riverbeds, glacial tills, and shorelines.

Other metamorphic or igneous specimens

See all

Garnetiferous Pegmatite

Pegmatite with Almandine Garnet and Muscovite

igneous

Milky Quartz with Iron Staining

Silicon Dioxide (SiO2)

mineral

Milky Quartz

Silicon Dioxide (SiO2)

mineral

Quartz with Muscovite Mica

Silicon Dioxide (SiO2) with Potassium aluminum silicate hydroxide fluoride [KAl2(AlSi3O10)(F,OH)2]

mineral

Milky Quartz

Silicon Dioxide (SiO2)

mineral

Milky Quartz

Silicon Dioxide (SiO2)

mineral