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I was thinking of crushing up some common limestone for microminerals because the water where I live has nearly zero calcium content. So I read about the trace elements of limestone and It says chromium is common at about 30ppm, and chromium VI is toxic, but it only occurs at tectonic boundaries and high-energy industrial processing.

If I crush up mountain limestone which is full of white calcite, what kind of nasty chemicals could result from that, compared to drinking water from a village fountain from the same area?

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  • $\begingroup$ Naively, I would think the water would tend to have similar soluble minerals in a mountainous region $\endgroup$ Commented Sep 5, 2022 at 14:03
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    $\begingroup$ Chromium in limestone might occur in our region of the world, but it may not be widespread. This is the first time I'm aware that chromium can occur in limestone. $\endgroup$
    – Fred
    Commented Sep 6, 2022 at 18:31
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    $\begingroup$ I found this reference here from Egypt, researchgate.net/figure/… $\endgroup$ Commented Sep 6, 2022 at 19:29

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Whether the chromium is Cr(III) or Cr(VI) while it's in the rock is less important than what could happen when the material is dissolved and thus exposed to air (which can also be dissolved or entrained in water). According to the Pourbaix diagram given by Mahiya and Lofrano1, oxygen (represented by the upper dashed line) can oxidize Cr(III) to Cr(VI). If your limestone sample has chromium, you may want to prudently assume it acts as a source of Cr(VI) when dissolved under our atmosphere.

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Chromium tends to occur in higher concentrations in mafic rock like basalt and sediments derived from them. So if you can remove such impurities from your limestone, the risk from chromium (and other heavy metals that tend to get into mafic rock) would be less.

Reference

  1. Mahiya, Suresh & Lofrano, Giusy & Sharma, Sanjay. (2014). "Heavy metals in water, their adverse health effects and Biosorptive removal: A review." International Journal of Chemistry. 3. 132-149. https://www.researchgate.net/publication/262763956_Heavy_metals_in_water_their_adverse_health_effects_and_Biosorptive_removal_A_review.
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  • $\begingroup$ It's not clear why you're mentioning mafic rocks -- we're talking about a sedimentary rock (limestone) and "mafic" is a term used to describe igneous rocks. $\endgroup$
    – Spencer
    Commented Mar 14, 2023 at 13:19
  • $\begingroup$ The igneous rocks then generate sediments. $\endgroup$ Commented Mar 14, 2023 at 13:49
  • $\begingroup$ Igneous rock sediments generate limestone? $\endgroup$
    – Spencer
    Commented Mar 14, 2023 at 14:19
  • $\begingroup$ Yes. Carbonic acid in the water can slowly attack rocks, and precipitate carbonates of calcium, magnesium, etc, oxides or hydroxides of iron and other transition metals, plus some other low-solubility salts such as calcium sulfate (gypsum). $\endgroup$ Commented Mar 14, 2023 at 14:37

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