About Blue Topaz

By irradiation with electrons, gamma rays or neutrons colourless topaz is modified to blue colours.
Radioactivity is only produced when irradiating with neutrons. Generally, topazes change to greenish-brown colour by irradiation and subsequently turn to blue by heat treatment. Gamma rays and electrons normally produce light blue colours ("sky blue"). Neutrons cause blue colours of higher intensity (e.g. "London Blue"). Combination techniques extend the blue colour variation, e.g. neutron plus electron bombardment produces the so-called "Swiss blue".

There exist also blue topaz gemstones naturally occurring in a light blue colour. They were irradiated by nature, not artificially. Though, artificially irradiated stones have such low values of radioactivity they do not harm humans in any way.

Facts:

• Mineral: Topaz
• Mohs Hardness: 8.0
• Specific gravity: 3.53 g/cm³