Ruby is a gemstone made of aluminum oxide, also known as mineral corundum. Ruby is named after its red color and is a part of the traditional cardinal gem family. In general, the quality of a ruby is assessed using its clarity, cut, and color. Ruby has a 9.0 on the Mohs Scale for hardness, making it one of the hardest naturally occurring materials. Ruby can be synthetically made and is often used in the field of metrology, particularly when making ball probes. Back to entire glossary
