metamorphic
Quartzite Pebble
Metamorphic Quartzite (SiO2)
Hardness of 7 on the Mohs scale, colors range from white to gray, yellowish, or brown due to iron oxide impurities. Luster is vitreous to greasy. Crystal structure is trigonal (microcrystalline or interlocking quartz crystals). Conchoidal fracture with no true cleavage.
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Physical properties
Hardness of 7 on the Mohs scale, colors range from white to gray, yellowish, or brown due to iron oxide impurities. Luster is vitreous to greasy. Crystal structure is trigonal (microcrystalline or interlocking quartz crystals). Conchoidal fracture with no true cleavage.
Formation & geological history
Formed from quartz-rich sandstone or chert that has been subjected to intense heat and pressure (regional or contact metamorphism). Geological age can range from Precambrian to Cenozoic.
Uses & applications
Used in construction, railroad ballast, road aggregate, manufacturing of silica brick, and sometimes as a decorative stone or tumbled polishing stone.
Geological facts
Quartzite is extremely durable and resistant to chemical weathering, which is why quartz-rich sandstone survives as high-relief mountain ridges and wears down into smooth pebbles in riverbeds and beaches.
Field identification & locations
Can be identified by testing hardness (scratches glass easily) and observing that it breaks across the quartz grains rather than around them, unlike sandstone. Common worldwide in river gravels, ancient stream beds, and mountainous regions.
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