igneous
Felsic Tuff
Pyroclastic volcanic rock (Tuff)
Hardness: 5-7 Mohs; Color: Grey to brownish with earthy weathering; Luster: Dull to earthy; Crystal structure: Microcrystalline to glassy matrix with embedded fragments; Specific Gravity: 1.7-2.5
- Hardness
- 5-7 Mohs
- Color
- Grey to brownish with earthy weathering
- Luster
- Dull to earthy
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Physical properties
Hardness: 5-7 Mohs; Color: Grey to brownish with earthy weathering; Luster: Dull to earthy; Crystal structure: Microcrystalline to glassy matrix with embedded fragments; Specific Gravity: 1.7-2.5
Formation & geological history
Formed from the accumulation and lithification of volcanic ash, glass, and mineral fragments ejected during explosive volcanic eruptions. It can range in age from recent to billions of years old.
Uses & applications
Historically used for construction (buildings and sculpture) due to its relative softness when first quarried and its light weight. Used as an aggregate in modern construction and as a decorative stone.
Geological facts
Tuff is the primary material of the famous Moai statues on Easter Island. When volcanic ash is hot enough to weld together upon landing, it forms 'welded tuff'.
Field identification & locations
Identify in the field by its gritty, abrasive texture and the presence of small, visible crystal or rock fragments (clasts) embedded in a fine-grained ashy matrix. Commonly found near active or extinct volcanic arcs.
