Color and the Ruby
Can a ruby be any color other than red? Well, not really. The ruby is the red version of the mineral corundum, which is a form of aluminum oxide. Corundum can be colors ranging from clear to green to blue, but only red corundum is called ruby. All other colors of corundum are called sapphires, although in some parts of the world pink corundum is also known as ruby.
Colors can vary within the ruby family as well, and are a large determinant of value. The most valuable rubies are a rich, red color – not too light and not too dark. Many rubies have yellow or blue undertones, which add to their individuality.
Rubies measure in at 9 on the MOHs gem hardness scale. In comparison, diamond comes in at 10 and tanzanite at around 6.5 to 7. The ruby’s high measurement on the scale tells us that it is a strong gem and is less likely to break or be scratched than gems that are lower on the scale. This is good news for those who like to wear ruby rings, since gems in rings tend to be knocked around more in the course of a day than gems in earrings or necklaces.
Size and Shape
Rubies come in sizes ranging from tiny to huge. You will see rubies in rings cut into a variety of shapes – round, marquise, pear – but oval is the most popular cut for rubies. Cabochon, or unfaceted, cuts are frequently used with lower quality rubies.
In general, rubies tend to be less clear than other types of gem quality corundum, so it is important to examine the stone closely for inclusions that can be seen without a jeweler’s loupe. All other factors being equal, the clearer the ruby, the more valuable it is.
Where Rubies are Found
Gem quality rubies are mostly mined in Asia, in countries like Burma, Vietnam, Sri Lanka, China, Pakistan and Afghanistan, but are also found in Tanzania, Africa and India.