Naturally occurring rubies are one of the world’s most valuable gemstones. They come from the mineral corundum, which is also the host for sapphires. However, only red corundum can be considered a ruby. Rubies range in colour from pinkish red to a deep, rich blood colour, often referred to as “pigeon’s blood”. With a hardness of 9 on the Mohs scale, rubies are second only to diamonds as the hardest material known to man. The Burmese mines have historically yielded the most sought-after rubies, though increasingly African rubies are considered highly desirable.