Quartz and halite have different crystal shapes primarily because of their different atomic arrangements and properties. The arrangement of atoms or ions inside the unit cell of a crystal determines its shape. Quartz is formed by silicon and oxygen atoms which arrange themselves in a three-dimensional lattice structure, resulting in a variety of crystal habits such as prismatic habits. On the other hand, halite is formed by sodium and chlorine ions, which arrange themselves in a cubic lattice structure, giving halite crystals a cubic habit.