Sea Water Salts

Images made through a microscope. All subject types.

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micro_pix
Posts: 355
Joined: Fri May 11, 2012 12:05 pm
Location: Southampton, Hampshire, UK

Sea Water Salts

Post by micro_pix »

Hi,

I let some seawater dry slowly on a slide over 24 hours and had a look under crossed polars. There were some lovely large NaCl crystals, which aren't anisotropic, but there were also some much smaller crystals which were. They weren't coloured under cross polarisation but they looked nice with a lambda plate inserted.

I assume that they are some sort of salt, possibly a sulphate, if any one knows what they are likely to be I'd appreciate the info.

Here's a collage of a few of the crystals, crossed polars with a lambda plate, Epi illumination, 20x objective.

Dave
Seawater Crystals
Seawater Crystals
Last edited by micro_pix on Tue Jul 28, 2020 12:47 am, edited 1 time in total.

Macro_Cosmos
Posts: 1039
Joined: Mon Jan 15, 2018 9:23 pm
Location: Sydney

Re: Sea Water Salts

Post by Macro_Cosmos »

Wow they look like small fluorite crystals, love the colour!

Pau
Site Admin
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Joined: Wed Jan 20, 2010 8:57 am
Location: Valencia, Spain

Re: Sea Water Salts

Post by Pau »

Almost for sure they will be gypsum or anhidrite, both Calcium sulphate.
Pau

micro_pix
Posts: 355
Joined: Fri May 11, 2012 12:05 pm
Location: Southampton, Hampshire, UK

Re: Sea Water Salts

Post by micro_pix »

.
Thanks for the input Marco and Pau.

I googled the concentration of the ions in seawater and after Chloride (0.546 moles/kg) Sulphate (0.0282 moles/kg) is the next most abundant anion, Ca is third most abundant cation. I also found a paper that covers the deposition of salts during seawater evaporation and all of the information points to Pau’s suggestion of CaSO4. Another interesting paper on crystal growth that looks at Halite, Calcite and Gypsum crystals.


Dave

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