What is Pleochroism?
Pleochroism an Optical Phenomenon
Pleochroism is an optical phenomenon seen in certain minerals and gemstones. Depending on the angle from which the stone is viewed, different colours can be seen.
Pleochroism can be used for identification purposes because stones that share very similars colour will often have different pleochroic colour schemes.
Although amethyst can exhibit pleochroism it's fairly weak. In tourmaline, tanzanite and apatite it's strong.
The word pleochroism comes from the Greek words 'pléōn' meaning 'more' and 'khrôma' meaning 'colour'.
Pleochroism is caused by the way light passes through a mineral's crystal struture.
The crystal in the photo above is an extreme example of pleochroism. The photo is clickable and redirects to the original image. The page includes further details about how the photo was taken. Courtesy of Stan Celestian.