Opal is a fan favorite gem with a supernatural look. Opal comes in five main types: white, black, fire, boulder, and water. Opals have a unique quality called play of color which describes how they show off different colors of the rainbow as you turn and look into the opal. Opal is fairly soft and is unique in that they need to kept out of extremely dry environments.
History and Etymology-
Opal most likely gets its name from the Sanskrit word úpala. In Roman times it was valued above all other gems because it contained the colors of all the other gems. In the middle ages, opal was known for being lucky and was thought to have the ability to make one invisible.
Opal is the birthstone for October.
Mohs hardness- 5 to 6.5
Refractive Index- 1.37-1.47
Specific Gravity- 2.15