sedimentary or metamorphic

Limonite-stained Quartz / Quartzite

Silicon Dioxide (SiO2) with iron hydroxides (FeO(OH)·nH2O)

Hardness: 7 (Mohs); Color: Tan/yellowish-brown due to iron oxidation; Luster: Dull/waxy (unpolished) to vitreous; Crystal Structure: Trigonal; Cleavage: None/Conchoidal fracture; Specific Gravity: 2.65.

Hardness: 7 (Mohs)
Color: Tan/yellowish-brown due to iron oxidation
Luster: Dull/waxy (unpolished) to vitreous

Identified April 17, 2026More sedimentary or metamorphic →

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Physical properties

Formation & geological history

Formed through the accumulation of quartz-rich sand and subsequent cementation or low-grade metamorphism. The yellow/brown staining occurs via secondary weathering where iron minerals oxidize into limonite or goethite, permeating the porous surface of the rock.

Uses & applications

Common quartzites are used in construction for road ballast and dimension stone. Stained specimens are occasionally used in 'river rock' landscaping or as decorative pebbles.

Geological facts

Quartz is one of the most chemically stable minerals on Earth's surface. The yellow coloring is essentially 'stone rust,' where iron-rich water has interacted with the silica over long periods of time.

Field identification & locations

Identify by its hardness (will scratch glass), lack of visible grains (unlike sandstone), and its resistance to acid (unlike limestone). It is commonly found in riverbeds, glacial tills, and weathered outcrops globally.

Other sedimentary or metamorphic specimens

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Shale or Argillite

Shale (sedimentary) / Argillite (metamorphic)

Sedimentary or Metamorphic (low-grade)

Milky Quartz with Iron Inclusions

Quartz (Silicon Dioxide, SiO2)

mineral

Anthracite Coal

Anthracite (Carbon-rich Sedimentary-to-Metamorphic Rock)

metamorphic

Anthracite Coal

Anthracite (Carbon-based sedimentary-derived metamorphic rock)

metamorphic

Jasper Conglomerate (Puddingstone)

Siliceous Conglomerate (Quartz and Jasper clasts in a fine-grained matrix)

sedimentary

River Pebbles and Quartz

Mixed Igneous, Sedimentary, and Metamorphic Rocks (Silicon Dioxide SiO2 dominant)

mixed