metamorphic
Quartzite with Dark Mineral Inclusions
Quartzite (primarily SiO2) with accessory minerals
Hardness: 7 on Mohs scale; Color: Mottled grey, white, and tan; Luster: Vitreous to dull; Crystal structure: Granular, non-foliated; Specific gravity: 2.6–2.7
- Hardness
- 7 on Mohs scale
- Color
- Mottled grey, white, and tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Mottled grey, white, and tan; Luster: Vitreous to dull; Crystal structure: Granular, non-foliated; Specific gravity: 2.6–2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure. Most quartzite dates from the Precambrian to Paleozoic eras. This specific specimen shows signs of river-tumbling (rounded edges).
Uses & applications
Used primarily in construction as crushed stone, road ballast, or decorative landscaping material. High-purity quartzite is used to produce ferrosilicon and industrial silica sand.
Geological facts
Quartzite is so tough that it usually breaks through the quartz grains rather than along their boundaries, unlike sandstone. It is resistant to chemical weathering and often forms the peaks of mountain ranges.
Field identification & locations
Identify by its ability to scratch glass and its granular, sugary texture. Common in Appalachian and Rocky Mountain regions (USA). For collectors, look for the 'sugary' sparkle on freshly broken surfaces.
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