It is next to impossible to answer because it depends on the solubility of the limestone into water. If you take pure CaCO3 and dissolve it in H2O with the solubility constant of 4.8 * 10-^9 , only 0.00015 mol/L will dissolve into the H2O.

If you take this poor mix of CaCO3 to water, you have a pKa of 9 and that equates to a pH = 5.

That means its acidic because in this case the CO3- ion mixes with the H2O to form carbonic acid, which is why the pH is acidic. But in some limestones you do get a basic condition where the acids of the ground elements are displaced by the Ca ion and you do get a basic soil from it. So it really depends on the additives.

Fact is that is very hard to determine pure limestone pH because of the many variables that can effecting it, both in the limestone itself and the liquids it comes in contact with.

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