metamorphic
Riverstone Quartzite (Water-worn Siltstone/Quartzite)
Metamorphosed Quartz-rich Arenite (SiO2)
Hardness: 7 (Mohs scale), Color: Grayish-white with brown iron-oxide staining/spotting, Luster: Dull to waxy, Crystal structure: Microcrystalline/Granular, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6 - 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Grayish-white with brown iron-oxide staining/spotting, Luster: Dull to waxy, Crystal structure: Microcrystalline/Granular, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6 - 2.65
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone or siltstone under intense heat and pressure, recrystallizing the silica. The rounded shape indicates extensive transport and mechanical weathering in a high-energy fluvial (river) or glacial environment.
Uses & applications
Commonly used as decorative landscaping stone, in aggregate for construction (concrete and road base), and sometimes as a natural worry stone or for decorative rock painting.
Geological facts
Quartzite is so durable that it often survives multiple cycles of erosion and mountain-building. The brown spots on this specimen are likely secondary mineralization—limonite or goethite staining that occurred after the stone was exposed to oxygenated water.
Field identification & locations
Identify in the field by its hardness (it will easily scratch glass) and its smooth, rounded 'pebble' texture. It lacks the layered cleavage of slate or the visible grains of sandstone. Commonly found in riverbeds, glacial tills, and beaches worldwide.
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