8.0 on the Mohs scale.

Brazil, U.S., Sri Lanka (Ceylon), Myanmar (Burma), former USSR, Australia, Pakistan, Mexico, Tasmania, Japan, Africa. Topaz and citrine are the birthstones of the month of November. Some blue topaz are indistinguishable from aquamarine with the naked eye. Most blue topaz is irradiated and heat treated silver topaz, although it is sometimes found naturally.

The names "Sky blue topaz", "Swiss blue topaz", "London blue topaz" are trade names which refer to the darkness of the gemstone, with "sky blue topaz" being the lightest and "London blue topaz" being the darkest.

Blue topaz is usually irradiated and often heated to produce blue color.

More information on gemstone enhancements.

Blue Topaz is a member of the Precious Topaz gemstone family.