HOW MINERALS FORM
Many of Earth's minerals form from Magma. Magma is melted rock that is underground. As the magma moves closer to the Earth's crust it begins to cool. As it cools the atoms inside the magma condense, moving closer together until it solidifies and forms crystals.
A crystal is a regular geometric solid with smooth surfaces. There are many different crystal shapes, and the exact shape of a minerals crystal is determined by the internal arrangement of atoms.
The size of a crystal is determined by the amount of time it takes the magma to cool. If the magma cools quickly, the crystals have less time to grow so they are smaller. Conversely, if the magma cools slowly the crystal has lots of time to grow, so they are much larger.
Fast Cooling = Small Crystals
Slow Cooling = Large Crystals
EVAPORATION OF WATER
Some minerals form when water containing dissolved substances evaporates. When the water evaporates it leaves behind the substances that were disolved inside it. For example, salt water contains Na and Cl. When salt water evaporates it leaves behind the Na and Cl atoms, which then combine to form the mineral Halite (which we know as salt).