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The crust of the Earth is made up of rocks, and rocks are made up of minerals.

Top: Diamond crystal, octahedron shape. Bottom: Cube shaped halite crystals (salt).

Minerals are naturally occurring substances which are stable at room temperature and possess a certain chemical composition. Minerals are identified by their characteristics: they have color, mass, and density, and may have taste or odor.

They also have particular shapes. A crystal is a mineral that has an ordered pattern based on its molecular structure. Diamond crystals have a different shape than salt crystals or quartz crystals. Salt crystals form cubical shapes. Quartz crystals have six sides ending in pyramids on the ends of the crystals. These different shapes help us tell one mineral from another. Crystals are formed when a substance in liquid form cools and solidifies. Crystals also form during the evaporation process, like when sugar crystals are left in the bottom of a cup after all the liquid evaporates.

In the image, you can see a diamond that has been extracted from the ground and crystalline salt. The top image of the diamond is rough and uncut, showing the shape of the octahedron crystal—eight planes with triangular faces—that naturally occurring diamonds possess. The bottom image shows halite crystals. Halite is a salt, so you can see the cube-like shape of the crystals.

Question

What is the difference between a quartz crystal and a salt crystal?

A salt crystal is a cube-like shape and a quartz crystal has six sides.