Minerals have an internal, crystalline structure. Molecules that make up the mineral are arranged in a set pattern. This crystalline structure is sometimes reflected as a crystal, if the mineral is given room to grow. However, even organic substances can grow crystals. For example, sugar which is organic, can make sugar crystals commonly called "rock candy." So not all crystals are minerals.

Minerals have a definite chemical composition. Minerals are always composed of the same elements. Minerals are rarely composed of one element. These native minerals, include gold, silver, copper, and sulfur. However, most minerals are made of compounds (combinations of two or more different elements). For example, halite (NaCl) or table salt, is always composed of only two elements, sodium (Na), and chlorine (Cl). Geologists classify minerals into chemical families based on their compositions. 

The crystal structure of halite. 
Red=Na, yellow=Cl