metamorphic
Iron-Stained Quartzite
Recrystallized Quartz (SiO2) with Ferruginous Oxides
Hardness: 7 on Mohs scale; Color: Yellowish-brown to rusty orange due to iron oxide staining; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Yellowish-brown to rusty orange due to iron oxide staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Yellowish-brown to rusty orange due to iron oxide staining; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz sandstone. Under intense heat and pressure, the sand grains recrystallize into a dense, interlocking mosaic of quartz crystals. The yellow-orange color is a result of secondary iron oxide (limonite or goethite) leaching into the rock.
Uses & applications
Commonly used as crushed stone for road construction, railway ballast, and as a decorative stone in landscaping. High-purity quartzite is used to produce silica for glassmaking.
Geological facts
Quartzite is so tough that it often survives intense weathering that destroys other rocks, frequently capping hills and mountain ridges. Unlike sandstone, quartzite will break across the grains rather than around them.
Field identification & locations
Identify by its extreme hardness (it will easily scratch glass and steel) and its granular, sugary appearance. Found globally in ancient mountain belts and shields. Collectors should look for distinct crystalline faces or interesting color bands.
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