Which is not an essential characteristic of any mineral? a. crystal structure b. solid c. formed by inorganic processes d. naturally occurring

Crystal structure is not an essential characteristic of any mineral.

Explanation:

The substance which have some distinct characters like they are naturally occuring,inorganic compound,which is solid in structure and have difinite chemical composition and ordered internal structure.

Naturally occuring because mineral is found naturally.

They are inorganic because the substance is made by any living organism  and are found in solid but not found in gas or liquid form

Different minerals have different chemical composition with a specific orderly arranged internal structure.

Example-Rock salt ( halite)

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.