metamorphic
Ruby in Marble
Corundum (Al2O3) in Calcite (CaCO3) matrix
Hardness: 9 on Mohs scale (for crystal). Color: Pinkish-red to deep pigeon-blood red gems in a white or grey matrix. Luster: Vitreous to sub-adamantine. Crystal structure: Trigonal/Hexagonal. Cleavage: None (has parting). Specific gravity: 3.97-4.05.
- Hardness
- 9 on Mohs scale (for crystal)
- Luster
- Vitreous to sub-adamantine
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Physical properties
Hardness: 9 on Mohs scale (for crystal). Color: Pinkish-red to deep pigeon-blood red gems in a white or grey matrix. Luster: Vitreous to sub-adamantine. Crystal structure: Trigonal/Hexagonal. Cleavage: None (has parting). Specific gravity: 3.97-4.05.
Formation & geological history
Formed via contact or regional metamorphism of limestone/marble. The presence of chromium provides the red color. These deposits are often found in metamorphic belts associated with the Himalayan orogeny.
Uses & applications
The ruby crystals are used in high-end jewelry as gemstones. The specimen itself is highly valued as a mineral display piece for collectors.
Geological facts
Rubies from Jeter, Hunza Valley, and Burma are globally famous. Ruby is the birthstone for July and represents passion and courage. High-quality natural rubies larger than 5 carats are rarer than diamonds of comparable size.
Field identification & locations
Identified in the field by the high hardness of the red crystals (scratching almost anything else) and the effervescence of the marble matrix when exposed to HCl. Common locations include Myanmar (Mogok), Vietnam, Afghanistan, and Pakistan.
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