They thought sapphire would relieve insanity, powdered jet would kill toothache, and topaz ease asthma. Some famous gems are believed to carry a curse.
Most gem stones are hard minerals.
Their colours range from the colourless transparency of diamonds to pure black. Some are mottled or banded. Others reflect light waves in sparkling brilliance. Gem minerals are usually crystal. Mineral crystals vary in size from huge blocks weighing many tons to tiny specks that can be seen only under a microscope.