Mineral

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Geology and Soil Mechanics

Wigan and Leigh College

COLOUR This is the colour in natural light TRUE COLOUR :of a pure mineral depends on the nature and arrangement of constituent ions. Minerals containing Al, Na, Ca, Mg and Ba= GENERALLY COLOURLESS or LIGHTLY COLOURED. Mineral containing:- Fe, Cr, Mn, Ni, Ti, Va and Cu= ARE COLOURED OFTEN DEEPLY. VALENCY:- can influence colour eg:DIVALENT Fe2+ PRODUCES COMMONLY GREEN COLOURS TRIVALENT Fe3+ PRODUCES RED, BROWN AND YELLOW COLOURS.

BONDING:can affect colour for example Carbon Atoms:DIAMOND = COLOURLESS GRAPHITE = BLACK. Colour may exist in identification, but it can often be unreliable, for example:QUARTZ ROCK CRYSTAL = COLOURLESS ROSE QUARTZ = PINK(stained by Ti) AMETHYST = PURPLE (stained by Mn) CAIRNGORM = BROWN( stained by Fe). However other minerals are more reliable:GALENA = lead grey colour CHALCOPYRITE = Brass yellow colour.

THE COLOUR OF A MINERAL SHOULD ALWAYS BE DESCRIBED WITH THE STREAK, SOMETIMES AS A CONTRAST. COLOUR VARIETIES ARE OBSERVED IN THE FOLLOWING MINERALS:FLUORITE, CALCITE, HEMATITE, HALITE.

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