Details
London Blue Topaz is topaz stone that has a specific medium blue color. It's darker than aquamarine or Swiss Blue Topaz, but lighter than what we normally look for in a blue sapphire. Topaz itself is a fluorinated aluminum silicate, and has a Mohs hardness of 8. London blue topaz is a medium to dark grayish blue, sometimes described as "steely" or "inky". ... But natural topaz occurs mainly in white (colorless) and brown; natural blue topaz is actually very rare