Chemicals dissolved in water. Calcite is a good example, if I'm not mistaken.
Molar solubility<span> is the number of moles of a substance (the solute) that can be dissolved per liter of solution before the solution becomes saturated. We calculate as follows:
</span>3Cu2+ + 2(AsO4)3-<span> = Cu3(AsO4)2
</span>
7.6 x 10^-36 = (3x^3)(2x^2)
x = 6.62 x 10^-8 M