A new fake mineral is currently circulating on the web and in particular eBay : ruby and sapphire crystals with bright colors and large dimensions (sometimes up to 5 cm). If these crystals are indeed natural corundum, they have in fact been artificially dyed with an organic coating to give them these bright colors (blue, red, and green to simulate the emerald !?!), And thus facilitate their sale... The dyes are concentrated in the roughness and cracks and give a shiny appearance to the crystals. The crystals are natural sapphires with gray and brown colors, sometimes slightly bluish from Madagascar.
These processed minerals are generally sold at low prices and the treatment is never disclosed.