metamorphic
Quartzite (Sugar Quartz)
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: White to yellowish-tan; Luster: Vitreous to dull; Crystal structure: Hexagonal/Trigonal (microcrystalline grains); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White to yellowish-tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to yellowish-tan; Luster: Vitreous to dull; Crystal structure: Hexagonal/Trigonal (microcrystalline grains); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. This recrystallization process fuses the individual quartz grains into a solid, durable rock matrix. Ages vary globally from Precambrian to more recent tectonic events.
Uses & applications
Used as a high-quality decorative stone, as crushed stone for road construction, in the manufacturing of glass and ceramics, and as a source of silica for metallurgical processes. Small 'sugary' specimens are popular for amateur geology collections.
Geological facts
Quartzite is so hard that it will scratch glass and even high-quality steel. In the stone industry, it is often confused with marble because of its color, but its extreme durability makes it a preferred choice for kitchen countertops.
Field identification & locations
Identify in the field by its grainy, 'sugary' texture and high hardness (it cannot be scratched by a knife). Commonly found in folded mountain belts like the Appalachians or the Alps, and in large glacial deposits. Collectors look for pieces with interesting iron-staining or visible crystal pockets.
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