There are many different shapes and kinds of crystals. For starters there are the shapes. There are about 22 crystal shapes. Some of them are cubes, hexagonal and prisms. All crystals are not the same shapes.
All perfect crystals have flat surfaces.
There are also the kinds. For example, there is basalt, salt, sand, quartz, granite, obsidian, shale, marble, slate, petrified wood, diamonds, snowflakes, rhyolite and felsite, they are all crystals. Basalt has crystals inside them. Quartz is the most common mineral, and is also distributed all over the world. Rock quartz can only be melted at a very high temperature.