If you were lucky enough to be born in the month of October, your birthstone is both tourmaline and opal. Tourmaline comes from the Sinhalese word for mixed colored stone, tura mali. In fact, tourmaline is not a single mineral, it is a group of minerals that have very different chemical compositions and colors. A tourmaline is a boron silicate mineral that occur within igneous and metamorphic rocks.

The other birthstone is opal, which gets its name from the Greek word opallios. This roughly translates into “to see a change in color” as demonstrated when you spin an opal. Opal forms when water picks up silica dioxide and deposits it into open voids or cavities along with trace impurities. The water then evaporates and leaves the silica dioxide. Most of the opal in the world is produced from Australia, where seasonal rains make it common for water to leach out silica and deposit it into cracks within the ground.