metamorphic
Yellow Quartzite (River Pebble)
Metamorphic Quartzite (predominantly SiO2 with iron oxide inclusions)
Hardness: 7 (Mohs scale); Color: honey-yellow, amber, or tan; Luster: waxy to vitreous; Crystal structure: trigonal (microcrystalline); Cleavage: none; Specific gravity: 2.6-2.7. It has a sugary texture under magnification.
- Hardness
- 7 (Mohs scale)
- Color
- honey-yellow, amber, or tan
- Luster
- waxy to vitreous
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Physical properties
Hardness: 7 (Mohs scale); Color: honey-yellow, amber, or tan; Luster: waxy to vitreous; Crystal structure: trigonal (microcrystalline); Cleavage: none; Specific gravity: 2.6-2.7. It has a sugary texture under magnification.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. This specific specimen has been chemically weathered and physically rounded by fluvial (river) transport, likely over thousands of years.
Uses & applications
Used as decorative garden stones, in lapidary work for tumbling, or historically as a hard material for tool making. Highly rounded 'river gold' quartz is popular in pebble collections.
Geological facts
Quartzite is so tough that it often survives long-distance transport in rivers that would crush other rocks. The yellow color is caused by trace amounts of limonitic iron staining that has permeated the grain boundaries.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife and its lack of reaction to acid. Look for it in riverbeds or glacial till where water-worn cobbles accumulate.
