metamorphic
Marble
Crystalline Limestone (mostly CaCO3 / Calcium Carbonate)
Hardness: 3 on Mohs scale; Color: White to off-white; Luster: Waxy to vitreous; Crystal Structure: Trigonal (granular texture); Cleavage: Rhombohedral (observable in individual grains); Specific Gravity: 2.6 - 2.8
- Hardness
- 3 on Mohs scale
- Color
- White to off-white
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 3 on Mohs scale; Color: White to off-white; Luster: Waxy to vitreous; Crystal Structure: Trigonal (granular texture); Cleavage: Rhombohedral (observable in individual grains); Specific Gravity: 2.6 - 2.8
Formation & geological history
Formed through the regional or contact metamorphism of limestone or dolostone. Under high pressure and heat, the calcite grains recrystallize into a dense, interlocking mosaic of crystals. Age varies by location, often associated with ancient mountain-building events.
Uses & applications
Used extensively in construction (countertops, tiles), sculpture due to its relative softness and 'glow', as an industrial chemical base, and in its crushed form for agricultural soil treatment.
Geological facts
Pure white marble, like the Carrara marble used by Michelangelo, is the result of metamorphism of very pure limestone. The 'glow' seen in marble sculpture is due to its low refractive index, which allows light to penetrate a short distance into the stone before being scattered.
Field identification & locations
Identify in the field by its sugary, crystalline texture and its reaction to dilute hydrochloric acid (it will fizz/effervesce). It is soft enough to be scratched by a copper penny or a steel knife. Commonly found in mountainous regions near convergent plate boundaries.
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