Blue topaz is a variety of topaz that has a specific blue hue obtained by treating white topaz. This semi-precious stone can vary in colour intensity from light shades of blue to deeper, more vibrant tones. The colour of blue topaz can be influenced by the presence of impurities or chemical elements in the crystal. It is also important to mention that topaz can be heat treated to enhance its colour.
In jewellery, blue topaz is often used to create rings, earrings, necklaces and other accessories. It is a fairly popular semi-precious stone because of its attractive colour and relatively high hardness. London, as a geographical reference, might suggest the possibility that the stone is associated with the London jewellery market, which is known for offering a wide range of quality gemstones and jewellery.