What is the birthstone color for people born in October?

The birthstone for the month of October is the opal. Common opal is usually colorless while the gem has a rich iridescent quality and changes colors.

The opal is the national gemstone of Australia, where 97% of the world's opals are produced. The stone was considered great luck in the Middle Ages, based on the belief that the color spectrum represented all the virtues.

There are several famous opal stones. The Queen’s Opal, or Andamooka Opal, was presented to Queen Elizabeth II when she visited Australia in the 1950s. According to the Guinness Book of World Records, the largest uncut black opal is the Halley’s Comet Opal. The size of a man’s fist, and weighing 1982.5 carats, it is the third-largest gem-grade black opal ever recorded.