igneous
Decomposed Granite
Grano-diorite/Granite-residuum (SiO2 primary)
Hardness: 6-7 (individual quartz/feldspar grains); Color: Tan, buff, gray, pinkish; Luster: Pearly to dull; Structure: Granular/fragmented; Cleavage: None (in bulk state); Specific Gravity: 2.6-2.7
- Hardness
- 6-7 (individual quartz/feldspar grains)
- Color
- Tan, buff, gray, pinkish
- Luster
- Pearly to dull
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Physical properties
Hardness: 6-7 (individual quartz/feldspar grains); Color: Tan, buff, gray, pinkish; Luster: Pearly to dull; Structure: Granular/fragmented; Cleavage: None (in bulk state); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the natural chemical and physical weathering of granitic rock over thousands of years; typically found in arid or semi-arid environments where rocks fracture into gravel and sand.
Uses & applications
Extensively used in landscaping, driveway surfacing, walking paths, and as a stable base for pavers. It is valued for its permeability and natural aesthetic.
Geological facts
Geologists often refer to this material as 'grus'. It is a signature feature of the Mojave and Sonoran Deserts, where vertical granite outcroppings crumble into large aprons known as bajadas.
Field identification & locations
Identify in the field by its sandy, gritty texture and the presence of small, angular chunks of quartz and potassium feldspar. Commonly found throughout California, Arizona, and the American Southwest.
