Natural occurrence

The Mogok Valley in Upper Myanmar (Burma) was for centuries the world's main source for rubies. That region has produced some of the finest rubies ever mined, but in recent years very few good rubies have been found there. The very best color in Myanmar rubies is sometimes described as "pigeon's blood." In central Myanmar, the area of Mong Hsu began producing rubies during the 1990s and rapidly became the world's main ruby mining area. The most recently found ruby deposit in Myanmar is in Namya (Namyazeik) located in the northern state of Kachin.
Rubies have historically been mined in Thailand, the Pailin and Samlout District of Cambodia, Afghanistan and in Pakistan. Rubies have rarely been found in Sri Lanka, where pink sapphires are more common. After the Second World War ruby deposits were found in Tanzania, Madagascar, Vietnam, Nepal, Tajikistan, and Pakistan. A few rubies have been found in the U.S. states of Montana, North Carolina, and South Carolina. More recently, large ruby deposits have been found under the receding ice shelf of Greenland. In 2002 rubies were found in the Waseges River area of Kenya.
There are reports of a large deposit of rubies found in 2009 in Mozambique, in Nanhumbir in the Cabo Delgado district of Montepuez.^[3]
Spinel, another red gemstone, is sometimes found along with rubies in the same gem gravel or marble. Red spinel may be mistaken for ruby by those lacking experience with gems. However, the finest red spinels can have a value approaching that of the average ruby.^[4]