1. Naturally Occurring: Minerals must be formed by natural processes, not man-made.

2. Inorganic: Minerals are not derived from living organisms. They are composed of elements and compounds found in the Earth's crust.

3. Solid: Minerals are solid, with a definite volume and shape.

4. Crystalline Structure: Minerals have a specific, repeating arrangement of atoms, giving them a characteristic crystal shape (though not always visible to the naked eye).

Let me know if you'd like more information about these criteria or want to explore specific examples!