Quartzite River Rock with Dendrites

Physical Properties

Hardness: 7 on Mohs scale; Color: Tan to light brown with dark brown/black dendritic markings; Luster: Dull to slightly waxy; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, often found in riverbeds where it has been smoothed by water erosion over millions of years. The dark patterns are mineral dendrites formed by manganese-rich mineral solutions seeping into micro-cracks.

Uses & Applications

Used in landscaping, as decorative pocket stones, for water filtration pebbles, and as construction aggregate. High-quality specimens with artistic dendrites are used in lapidary work.

Geological Facts

The tree-like patterns are often mistaken for fossils but are actually inorganic mineral growths called dendrites. Quartzite is so hard that it will scratch glass and even high-grade steel.

Field Identification & Locations

Identify by its hardness (cannot be scratched by a steel nail) and its smooth, rounded 'river stone' texture. Commonly found in ancient riverbeds or coastal deposits. Collectors look for unique dendritic patterns that resemble landscapes.

Identified on: 5/1/2026

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