What is the chemical formula of a natural magnet, specifically lodestone?

A natural magnet, often called lodestone, is primarily made of magnetite.

The chemical formula for magnetite is $\text{Fe}_3\text{O}_4$.

A. $\text{FeO}_4$
B. $\text{Fe}_3\text{O}_2$
C. $\text{Fe}_2\text{O}_3$
D. $\text{FeO}$

Option A, $\text{FeO}_4$, is likely a typographical error and is intended to be $\text{Fe}_3\text{O}_4$, which is the correct formula for magnetite. Among the given choices, this is the most appropriate answer.

The final answer is $\boxed{\text{A. FeO}_4}$ (assuming it is a typo for $\text{Fe}_3\text{O}_4$).