Orange Quartzite / Quartz River Siltstone

Physical Properties

Hardness: 7 (Mohs scale), Color: Orange to peach due to iron oxide impurities, Luster: Vitreous to waxy (especially when water-worn), Crystal structure: Trigonal/Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific gravity: ~2.65

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone or siltstone. Intense heat and pressure cause the quartz grains to recrystallize and fuse together. The orange hue is typically the result of hematite or limonite inclusions that occurred during or after sedimentation.

Uses & Applications

Commonly used as decorative landscaping stone, in aquarium gravel, or as aggregate in construction. High-purity quartzite is used in glass and ceramic manufacturing.

Geological Facts

Quartzite is so hard that it will scratch glass and steel. This specific specimen has been 'well-rounded' by tumbling in water, likely from a riverbed or coastal environment, which gives it its smooth, pebble-like appearance.

Field Identification & Locations

Identify in the field by its hardness (cannot be scratched by a knife) and its grainy, 'sugary' texture on broken surfaces. It is found globally in mountainous regions or ancient river deposits.

Identified on: 4/22/2026

Mode: Standard