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Gemstone Crystal Composition and Color
The chemical crystal composition in a ruby is Al2O3, also known as the mineral form of aluminum oxide. Ruby is the red version of the stone corundum, in which its reddish color comes from the fact that in the crystal composition small amounts of Chromium replace some of the Aluminum in the chemical structure.In a red ruby the chemical ratio of chromium to aluminum is about one to 5000. Shades of rubies can be found in red, pinkish, purplish, orange and brownish, although pink and other colored corundum is usually considered to be a colored sapphire. The main reason for the difference in color is due to the amount of Chromium or other trace minerals found.
Gemstone Crystal Hardness
The ruby crystal hardness is measured to be a nine on the Mohs hardness scale,with ten being the hardest. The hardness of the gemstone makes it excellent for the use in jewelry, as it is very durable. Ruby crystals that contain more inclusions and impurities are less hard and more likely to fracture.
Refrative Index
The refractive index is how fast light moves through an object versus how fast it travels in a vacuum. The refractive index of a ruby crystal is 1.75 to 1.77, which mean that light travels through a vacuum 1.75 to 1.77 times faster than it does through a ruby. When light shines through a ruby crystal, the light refracts, which means that it changes directions inside the crystal, so the light does not simply shine straight through but bends at an angle according to the refractive index value. The angle in which the light is refracted inside of the ruby is what causes the gemstone sparkle.
Shape
The shape of the crystal of gemstones, also known as crystallography, is triangular arranged into hexagonal prisms. Each unit cell, Aluminum Oxide and Chromium (Al2O3Cr), forms a triangle and in turn bonds to other unit cells to form a hexagon shaped crystal. This means that the Aluminum, Oxygen and Chromium bond together to form a triangle shape. Each of these triangular shaped units then bond together to form a hexagon shape. Therefore, natural ruby crystals are found in rocks in the shape of a hexagon.