Sheared rubyA rather nice little crystal of red corundum from the Mogok stone tract of Burma testifi

Sheared rubyA rather nice little crystal of red corundum from the Mogok stone tract of Burma testifies to the geological forces accompanying its birth and subsequent life in the crust. The gems themselves were born in the fire and pressure of metamorphism during the Himalayan mountain building event, as marine limestones were baked and recrystallised into marbles. The aluminium liberated in the process mixed with oxygen to form the corundum since it doesn’t fit into the calcite crystals in the forming marble, also sucking into its crystal lattice the chromium that gives it its colour. The forces are still present and the mountains are tectonically active, and at some later point the crystal was snapped by shear forces, part of the response of crust when it forcible meets other crust.LozImage credit: Dick Hughes -- source link

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