Here's what the formula means:

* (Mg,Fe): This indicates that olivine is a solid solution, meaning it can contain variable amounts of magnesium (Mg) and iron (Fe). The ratio of Mg to Fe can vary, creating different types of olivine.

* ₂: This subscript indicates that there are two magnesium or iron atoms per molecule.

* SiO₄: This represents the silicate anion, which consists of one silicon atom (Si) bonded to four oxygen atoms (O).

Therefore, olivine's chemical formula encompasses a range of possibilities depending on the specific ratio of magnesium and iron present.