Blue Topaz 

Natural blue topaz is rare and often found in quite pale colours.  The vast majority of blue topaz sold today owes its colour to irradiation and consequent annealing (heating) processes.  The main colours of blue topaz are sold under colour groupings dependant on the depth of blue.  The groups are  called: SKY/LIGHT BLUE (pale coloured), SWISS/MEDIUM blue (mid coloured) and London blue (deep coloured) although there is now an intermediate shade of blue between the sky and SWISS/MEDIUM blue colours known as ‘baby’ blue topaz.  Blue topaz is commonly available in all sizes and shapes and is popular in inexpensive to moderately priced jewellery.

Mohs’ Hardness: 8
Specific Gravity: 3.56-3.57
Refractive Index: 1.609-1.620
Birefringence: 0.008-0.010
Optic Sign & Character: Biaxial Positive
ICA Code: T
Treatments: Irradiation and heating
Incidence: Very common
Purpose: To induce blue colour
Durability: Moderate to good
Special Care: Avoid hard bumps and knocks
Synthetics: None
Possible Imitations: Synthetic spinel, glass, CZ