Author Topic: (Dis)colouration of calcite & minerals.  (Read 1664 times)

Offline Stuart Anderson

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(Dis)colouration of calcite & minerals.
« on: March 02, 2007, 05:24:03 pm »
Learned (ahem!!cough!!splutter!!) members of UKcaving...

Calcite discolouration and the associated minerals (other) that causes it...

Green - Copper (?)

What others?

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Re: (Dis)colouration of calcite & minerals.
« Reply #1 on: March 02, 2007, 05:33:14 pm »
Green - Copper - Yes.
red - iron and something in Lead mines too?
Yellow -? (no not people urinating on them ewww)
Brown - ? (no not...)

Offline Cap'n Chris

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Re: (Dis)colouration of calcite & minerals.
« Reply #2 on: March 02, 2007, 05:47:05 pm »
Colouration of speleothems has a variety of causes, including organic/humic acids/substances giving rise to vivid oranges, reds and less vibrant tan, orange and brown/dark brown colours, also incorporated transition metal ions usually in association with ore deposits which can result in green, yellow, blue and other variant colours than the common tans and oranges, then again there is colouration resulting from inorganic pigments often represented by Iron and manganese oxides, commonly resulting in red/maroon, browns and yelllow-browns (similar colours to those caused by humic acids) but with distinctions being possible by analysis using infrared light, manganese, carbon and carbon-bearing materials will result in darker/black deposits but can also be caused by soot (carbide/campfires), guano, tar, humates and partially decayed plant material. A non-exhaustive summary (I've probably missed lots out, so please add/alter/correct):

White = calcite/aragonite
Grey = manganese/lead blending with calcite
Yellow = ore deposits/ochre/iron
Tan = ditto but also organic/humic material
Orange = ditto, ditto
Brown = ditto, ditto, goethite/limonite, haematite
Red = vivid reds mostly caused by humic/fulvic acids
Pink = cobalt (depending on the crystal structure)
Maroon = ditto, haematite
Green = copper (in small concentrations), nickel salts
Blue = copper (in larger concentrations), chromium (if deposited in silicate minerals), cobalt
Black = manganese, iron, carbon, organic sources
A comprehensive study was done by K. Nassau in 1983 (The Physics and Chemistry of Colour: New York: Wiley).
« Last Edit: March 02, 2007, 11:18:58 pm by cap 'n chris, Reason: spelling errors »

Offline shotlighter

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Re: (Dis)colouration of calcite & minerals.
« Reply #3 on: March 02, 2007, 05:48:46 pm »
Black - Iron (as well as the better known red/orange colouring) & Manganese
Blue - Copper (Azurite) Cobalt.
Yellow (IIRC) - Iron again (Limmonite?)


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