Olivine has what two positive cations in its silicate structure?

Ferrous (Fe²⁺) and magnesium cation (Mg²⁺).

Explanation:

The olivine mineral is a type of orthosilicate, which is generally yellow to yellow-green in color. It is the main component of the upper mantle of the Earth, which can be found in igneous and metamorphic rocks.

The olivine mineral exists in the form of Mg₂SiO₄, Fe₂SiO₄, or (Mg, Fe) ₂SiO₄.

This silicate consists of two divalent cations, ferrous (Fe²⁺) and magnesium cation (Mg²⁺).