Author Topic: OFD: Selenite tunnel: speleothems: colour: why?  (Read 662 times)

Offline Ralf

  • regular
  • *
  • Posts: 51
    • Finnish caving association
OFD: Selenite tunnel: speleothems: colour: why?
« on: June 16, 2017, 07:59:35 pm »
Geology/mineralogy: Could someone please explain to me the colour of the speleothems in Selenite tunnel in OFD. Why the caramel/orange colour? Selenite? Gypsum? Sulphur? If so, why is there gypsum in a limestone cave?

Offline AR

  • Black shadow
  • junky
  • ****
  • Posts: 867
  • PDMHS, ATAC, ANHMS
Re: OFD: Selenite tunnel: speleothems: colour: why?
« Reply #1 on: June 16, 2017, 09:55:01 pm »
If you get iron pyrites present in veins/faults within the limestone then it'll tend to decompose in contact with water and form sulphuric acid as part of the process. That will then react with the limestone forming selenite, and take up some of the iron when it crystallises out giving it the colouration.
Dirty old mines need love too....

Offline mikem

  • forum hero
  • *****
  • Posts: 1805
  • Mendip Caving Group
Re: OFD: Selenite tunnel: speleothems: colour: why?
« Reply #2 on: June 17, 2017, 08:48:35 am »

Offline Ralf

  • regular
  • *
  • Posts: 51
    • Finnish caving association
Re: OFD: Selenite tunnel: speleothems: colour: why?
« Reply #3 on: June 20, 2017, 07:05:11 pm »
Thanks! I feel educated now  :smartass:

Offline Fulk

  • forum hero
  • *****
  • Posts: 3288
Re: OFD: Selenite tunnel: speleothems: colour: why?
« Reply #4 on: November 23, 2017, 06:48:17 pm »
I've a dim recollection of someone analysing orange stal. by dissolving it in acid and analysing the resulting solution. To their surprise they found no trace of iron, and eventually discovered that the orange colour was caused by the presence of the organic matter that stains peat run-off reddy-brown.

Offline Pegasus

  • NCC
  • Administrator
  • forum hero
  • *****
  • Posts: 1771
Re: OFD: Selenite tunnel: speleothems: colour: why?
« Reply #5 on: November 23, 2017, 10:37:37 pm »