Whle sapphire occurs in many colours, including yellow, green and orange, the most well known one is blue, in all its shades. The horizontal colour banding proves its natural origin, and the colour in this cluster is typical of its locality of origin: Ceylon/Sri Lanka. The gems here occur in alluvial placer deposits, as the original mother rock has eroded away over the aeons, but they represent the pulse of metamorphism that accompanied the welding together of the supercontinent Gondwana some half a billion years ago, leaving lovely metamorphic gems strewn across the landscapes of several continents, a region that I call the gemlands (see http://tinyurl.com/k6464q6).
Lanka sapphires are typically a paler blue, compared to the electric soft blues of Kashmir or the dark inky ones of Australia and Thailand. Of course these days most sapphires are heat treated to improve both colour and clarity, and wide diversities of colour found in nearly every mining area, but the traditional names often stick. Expensive stones are often sold with a certificate of origin, an assessment based on inclusions (long rutile needles in Sri Lanka’s case), growth patterns in the blue colour lines and trace element geochemistry. The specimen exhibits the typical hexagonal barrel shape and horizontal striations across the width of the crystal of corundum crystals.
Image credit: Heritage Auctions