Dot between the molecular formula of compounds

[donaldparida]

I have seen many instances of molecular formulas of two or more compounds with a dot between two adjacent molecular formulas like CuSO4.10H20, CaCO3.MgCO3, K2SO4.Al2(SO4)3.24H20 and so on. What does the dot indicate?

 

[Borek]

That the substance can be thought of as if it was a stoichiometric (that is, in a simple, constant ratio) mixture of other substances. Sometimes they can be separated, sometimes they can't, so there is no deeper meaning.

 

[Ygggdrasil]

Generally, it refers to substances non-covalently associated together, such as the case of hydrates.

 

[Borek]

substances non-covalently associated together

You are right that's what we usually mean when it comes to hydrates, but the same notation is used also for other situations. Sometimes minerals are written in the oxide form (at least that's how it is called in Polish), like spinel being MgO⋅Al₂O₃. Also dolomite MgCO₃⋅CaCO₃ is hardly made of non-covalently associated entities.