Pleochroism may be extreme, with trichroic colours ranging from : colourless, pale yellow or red; sky to lavender blue, or bluish-green; to dark blue.
22.
In addition to simple body colour, minerals can have various other distinctive optical properties, such as play of colours, asterism, chatoyancy, iridescence, tarnish, and pleochroism.
23.
Although bursaite's color is usually gray, its weak pleochroism can give it a whitish-blue tinge, and its strong anisotropy yields colors ranging from blue to yellow.
24.
Faceted andalusite stones give a play of red, green, and yellow colors that resembles a muted form of iridescence, although the colors are actually the result of unusually strong pleochroism.
25.
Pleochroism is visible, with the crystal appearing colourless when viewed along X or Y, and pale red when viewed along Z . Pleochroism should not be present if the mineral is colourless.
26.
Pleochroism is visible, with the crystal appearing colourless when viewed along X or Y, and pale red when viewed along Z . Pleochroism should not be present if the mineral is colourless.
27.
Crystals are translucent purple, but show distinct pleochroism ( from pale purple to pale bluish grey, depending on the angle of observation ) and leave pink streaks when rubbed on a flat surface.
28.
Reflected light anisotropism is the property of appearing to change color when viewed under plane polarised light is white, with very dark red internal reflections and very weak pleochroism in air, fair in oil.
29.
Play of colour, such as in opal, results in the sample reflecting different colours as it is turned, while pleochroism describes the change in colour as light passes through a mineral in a different orientation.
30.
Its color in plane-polarized light is dark red, and it does not exhibit pleochroism, which means it does not appear to be a different color when observed at different angles under a polarizing petrographic microscope.
