igneous

Rhyolitic Tuff (Breccia Type)

Rhyolitic Pyroclastic Rock (Mixed Silicates including Quartz, Feldspar, and Volcanic Glass)

Hardness: 5-7 (variable); Color: reddish-brown, tan, and earthy pink; Luster: dull to earthy with occasional glassy inclusions; Structure: clastic/fragmental texture; Cleavage: none; Specific Gravity: 2.3-2.6.

Hardness: 5-7 (variable)
Color: reddish-brown, tan, and earthy pink
Luster: dull to earthy with occasional glassy inclusions

Identified March 11, 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 explosive volcanic eruptions where magma, ash, and rock fragments are ejected and later lithified. This specimen likely dates from the Cenozoic era and formed in an continental volcanic arc environment.

Uses & applications

Used primarily as lightweight construction aggregate, road base material, and historical building stone. Small colorful specimens are popular for amateur geology collections.

Geological facts

Tuff can be so light it floats in water (if porous enough), and famous structures like the moai statues of Easter Island were carved from similar volcanic pyroclastic rocks.

Field identification & locations

Identify in the field by its 'chunky' or fragmental appearance and gritty texture. It is commonly found in volcanic regions like the Western United States (Nevada, Arizona, New Mexico) and around active or dormant volcanic arcs.

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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral