Blue Sapphire

Overview

Blue sapphire is the blue variety of corundum, coloured by trace amounts of iron and titanium. It is one of the "big three" coloured gemstones alongside ruby and emerald, and has been a stone of royalty and clergy for centuries. The British Crown Jewels feature some of the world's most famous sapphires.

Physical Properties

Mohs hardness: 9. Refractive index: 1.762 to 1.770. Specific gravity: 3.95 to 4.03. Crystal system: trigonal. Blue sapphires show strong dichroism, appearing violetish-blue in one direction and greenish-blue in another. Unlike rubies, blue sapphires rarely fluoresce strongly under UV light due to their iron content.

Colour and Quality

The ideal blue sapphire colour is a vivid, medium-toned, slightly violetish blue, known in the trade as "cornflower blue" (especially when associated with Kashmir origin). Stones that are too dark appear inky and lose brilliance. Stones that are too light look washed out. The best colour maintains its vibrancy in both daylight and incandescent light. Kashmir sapphires owe their legendary "velvety" appearance to microscopic inclusions that scatter light within the stone, creating a softness to the colour that is unique and irreproducible through treatment.

Major Sources

Kashmir: The Paddar deposit (discovered 1881) produced the world's most valued sapphires. Mining is essentially dormant. Sri Lanka (Ceylon): The oldest continuously mined source, producing sapphires for over 2,000 years. Ceylon sapphires tend toward lighter tones with excellent brilliance. Myanmar (Burma): Mogok produces vivid blue sapphires, often with a slight violetish hue. Madagascar: A significant source since the late 1990s, producing a range of qualities including some very fine stones. Australia, Thailand, Cambodia, Tanzania, and Montana (USA) also produce notable sapphires.

Vedic Significance

Blue sapphire (Neelam) represents Saturn (Shani) in Vedic astrology. It is considered the most powerful of the nine planetary gemstones, capable of producing dramatic positive or negative effects. Astrologers typically recommend a trial period of 3 to 7 days, wearing the stone wrapped in a blue cloth and placed under the pillow, before committing to set it in jewellery. The stone should be natural, unheated, and set in silver or panchdhatu. It is traditionally worn on the middle finger of the right hand on a Saturday.

Treatment

Heat treatment is standard practice. Most commercial sapphires are heated to improve colour and clarity. Beryllium diffusion treatment is used to add or modify colour, and lattice diffusion can create star effects. GTCL tests all sapphires for these treatments.