Semi Precious Gems
The Minerals that are colourless in their pure form are known as Allochromatic Minerals. These minerals show colours due to the presence of small quantities of “Colouring” agents. Corundum, Spinel, Beryl and Quartz are the examples of such minerals. Nickel, Cobalt, Titanium, Vanadium, Chromium, Manganese, iron, copper & Nickel are the examples of ‘Colouring Agents’.