metamorphic
Quartzite / Quartz Geodeoid Nodules
Silicon Dioxide (SiO2)
Mohs hardness of 7, sugary to coarse crystalline texture, dull to vitreous luster, light brown to tan color with visible quartz grains. Very hard and resistant to scratching by steel.
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Physical properties
Mohs hardness of 7, sugary to coarse crystalline texture, dull to vitreous luster, light brown to tan color with visible quartz grains. Very hard and resistant to scratching by steel.
Formation & geological history
Formed by the metamorphism of quartz sandstone under high heat and pressure, or as secondary silica mineralizations forming nodules or geode exteriors in sedimentary strata.
Uses & applications
Used as construction aggregate, decorative landscaping stone, crushed stone for rail ballast, and as lapidary material if hollow with internal quartz crystals.
Geological facts
Quartzite is so durable that it resists chemical weathering and often forms prominent hills and ridges as surrounding rocks erode away.
Field identification & locations
Identified in the field by its extreme hardness (scratches glass) and sugary fracture surface where breaks occur through individual quartz grains rather than around them.
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