Composition of Rubies

Mineralogical Classification

• The ruby is a type of corundum, which is an aluminum oxide: the chemical formula for corundum is Al2O3.

Ruby Color

• The red color of ruby comes from minute amounts of chromium, which makes the chemical formula for ruby Al2O3:Cr; the chromium 3+ ions replace aluminum 3+ ions.

Considerations

• When a ruby contains needle shaped growths of rutile, a form of titanium dioxide, its value is enhanced, as the ruby can then be cut to make a star ruby.

Synthetic Ruby

• There are a variety of ways to produce synthetic rubies, including flame fusion and flux, hydrothermal and Pulling processes, which, in various ways, include the basic corundum formula with chromium and other chemicals. The most common synthetic ruby manufacturing process is flame fusion, which fuses the basic chemicals for ruby with barium fluoride.

Misconceptions

• In some cases, a dopant, or chemical impurity, is added to the synthetic ruby mix to identify the ruby as unnatural, but this isn't always done.