In arid lake sediments, there may be salt phase precipitation. But in our new sediment core, we find a 10-cm thick salt layer comprising of gravel-like crystalline particles. They look like semi-transparent with half rounded edges and corners. The surface is uneven. Dark muddy deposits were filled between them. The samle is from arid central Asian. The salt layer is located at top 20-30 cm (Late Holocene). So far this lake is saltwater to saline lake.
How can we quickly identify these crystalline particles? Using the microscope? except for XRD method. We guess they might be gypsum or halite? It does not like calcite.
For quick identification you can test crystals for solubilyty in water or better in acetic acid solution(vinegar). if good soluble in water or vinegar - probably it is halite,If not - gipsum. if you can see gas evolution in acid - it could be calcite\dolomite.
handhed XRF spectrometer could be usefull for field testing.
Dear Eduard Rusanov,
Thank you very much for your advices. We tried it. It wasn't salty. According to XRF results and water ions, we infer that it should be mirabilite. The S element shows peak areas than other all element.
This means Sulfate precipitation in the lake sediments, maybe the lake was already very dry at that time.
Best wishes,
Hao
I think you can know this from the solubility of each salt. The sodium chloride salts (halite) are quick to soluble compared to the calcium sulfate salts (gypsum), while gypsum is faster soluble compared to the calcium carbonate salts (lime).
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