Topaz

Overview

Topaz is an aluminium fluorosilicate that forms large, clean crystals with a bright, glassy lustre. At 8 on the Mohs scale it resists scratching well, but it has perfect cleavage in one direction, so a sharp blow can split it. Topaz is found in many colours, and the most valuable are natural orange to pinkish orange stones known as imperial topaz.

Colour

• Imperial topaz: golden orange to reddish orange and pink, classically from Ouro Preto in Brazil. The most prized and the most expensive.
• Pink and red: rare naturally (Pakistan is a source); many pinks are heated yellow-orange topaz.
• Blue: very rare in nature. The sky, Swiss and London blue topaz in jewellery is colourless topaz that has been irradiated and heated.
• Colourless, yellow and light brown: common and affordable.

Key properties

Where topaz comes from

Brazil is the main source of imperial and colourless topaz. Pakistan produces natural pink topaz; Sri Lanka, Nigeria, Russia's Ural mountains, Mexico, Namibia and the United States are other sources.

Treatments

Nearly all blue topaz is irradiated and then heated; the colour is stable and the stones are safe to wear. Some pink topaz is created by heating yellow-orange stones. "Mystic" and other rainbow topaz has a thin coating on the surface that can wear or scratch. All treatments should be disclosed.

Buying tips

• Imperial topaz deserves a report. Confirm the colour is natural.
• Expect clean stones. Faceted topaz is usually eye-clean.
• Choose protective settings for rings, so the stone's corners and girdle are shielded from knocks.
• Ask whether a stone is coated before buying "mystic" or other iridescent topaz.

Care and cleaning

Clean only with warm soapy water and a soft brush. Never use ultrasonic or steam cleaners, avoid high heat and sudden temperature changes, and take topaz rings off for sport or heavy work. Clean coated stones gently and avoid abrasive cloths.