Final answer:
The angles between adjacent crystal faces of a mineral are always the same because they are defined by the mineral's specific atomic arrangement and crystal structure.
Step-by-step explanation:
The angles between adjacent crystal faces of the same type of mineral are always the same. This is a fundamental property of crystalline materials and stems from the highly ordered arrangement of atoms within a crystal lattice. Each of the seven crystal systems has characteristic angles and edge lengths. Independent of the size of the crystal or the conditions under which the crystal was formed, these angles remain constant for a given mineral. This consistency in angles is due to the specific arrangement of atoms and the repeating geometric pattern that defines each mineral species. Therefore, the correct answer to the question is 'a. are always the same.'