metamorphic
Ferruginous Quartzite (Iron-stained Quartz)
Silicon Dioxide (SiO2) with Ferric Oxide (Fe2O3)
Hardness: 7 (Mohs scale); Color: Yellow-brown, tan, and grey; Luster: Pearly to dull when weathered, vitreous when broken; Crystal Structure: Hexagonal (microcrystalline/massive); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Yellow-brown, tan, and grey
- Luster
- Pearly to dull when weathered, vitreous when broken
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Physical properties
Hardness: 7 (Mohs scale); Color: Yellow-brown, tan, and grey; Luster: Pearly to dull when weathered, vitreous when broken; Crystal Structure: Hexagonal (microcrystalline/massive); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. The distinct yellow and brown coloration is due to the oxidation of iron-bearing minerals or the infiltration of groundwater containing dissolved iron (hematite or goethite) into the rock's pores.
Uses & applications
Used primarily as construction aggregate, road ballast, and sometimes as a decorative stone in landscaping. High-purity quartzite is used to produce glass and silica brick.
Geological facts
Quartzite is so tough that it usually breaks through the quartz grains rather than around them. The iron staining often creates 'landscape' patterns inside the stone that collectors find aesthetically pleasing.
Field identification & locations
Identify in the field by its high hardness (it will easily scratch glass or a steel knife) and its grainy, sandpaper-like texture. Commonly found in mountain belts and ancient shield areas like the Appalachians or the Canadian Shield.
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