metamorphic
Quartzite (Gold-toned)
Crystalline Quartz Metamorphite (SiO2)
Hardness: 7 (Mohs), Color: Yellow-brown/Tan/Gold, Luster: Dull to vitreous, Crystal structure: Hexagonal (microcrystalline), Fracture: Conchoidal to irregular, Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs), Color: Yellow-brown/Tan/Gold, Luster: Dull to vitreous, Crystal structure: Hexagonal (microcrystalline), Fracture: Conchoidal to irregular, Specific gravity: 2.65
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure (metamorphism). This causes the quartz grains to recrystallize and fuse into a dense, hard rock. Often found in orogenic belts.
Uses & applications
Construction aggregate, railroad ballast, decorative stone in landscaping, and sometimes as a source of silica for glass manufacturing. Polished pieces are used in jewelry.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming resistant ridges and hilltops. It is frequently mistaken for gold ore when it contains mica flakes or iron staining.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by a steel blade) and its granular, sugary texture on fresh breaks. Common in riverbeds and mountainous terrain globally.
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