People that do rock climbing and weightlifting usually use magnesium carbonate on their hands to decrease slippery hands.

I would like to know how can someone that buys MgCO3 can really be sure it's magnesium carbonate and not another thing.

Is there a simple test people could do at home?

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    $\begingroup$ Magnesium carbonate is dirt-cheap and I can hardly imagine why anyone would substitute it with anything else. Are you trying to proof it's mostly MgCO3, or discover any third-party (organic/inorganic) components in there? $\endgroup$
    – andselisk
    Dec 17 '17 at 3:53
  • $\begingroup$ @andselisk, I'm trying to discover if it's mostly MgCO3. I imagine the manufacturer could add calcium carbonate (CaCO3) or something else into it without the customer knowing it. $\endgroup$ Dec 17 '17 at 11:34
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    $\begingroup$ Flame test can tell you something. The title is misleading as for identifying X is one thing. Assuring that only X is in there is a whole different story. $\endgroup$
    – Alchimista
    Dec 17 '17 at 12:54

If all you want to know is the relative amounts of calcium and magnesium carnbonates disolve it in vinegar (it will fizz). Now add lye until the pH is about neutral (use pH test strips) in order to neutralize any excess acid. Obtain a test kit for determining water hardness that will give both the magnesium and calcium hardness values for a sample. Dilute with DI (or nearly DI i.e. RO) water to be within range of the kit Be sure you understand what units the kit is reporting in. Usually it is units related to the equivalence of the calcium and magnesium so that if calcium harness turns out to be 1/5 magnesium hardness that tells you the original mix has 1/5 of a mole of CaCO3 for each mole of MgCO3.


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