The largest deposits of sapphires are found in Madagascar, Eastern Australia, East Africa, China, Sri Lanka, Thailand and Montana. At one time, Madagascar produced more than half of the world's sapphire supply. These gemstones are mined from igneous and metamorphic rock.
In the early 21st century, Madagascar generated about half of the world's sapphires following the discovery of a large deposit. It was not long after the discovery that the easiest-to-extract sapphires were removed and miners began digging more deeply to find additional gemstone deposits.
When found within a whole rock, a sapphire is considered part of a primary deposit. Sapphires discovered in stream beds, where they are released after a rock is fractured, are considered secondary deposits. However, over time, if a significant number of sapphires accumulate in a particular stream or river, the spot is known as an alluvial deposit. These are generally the most lucrative deposits for miners, as the high concentrations of gemstones are easy to remove. Those hunting for alluvial sapphires are able to do so with as little as a sieve, basket or pan. Most countries with significant quantities of sapphires strictly regulate the removal of the gemstone to avoid overuse of the land.