why do crystals made from different chemicals have different shapes?

Question

-------->what is a crystal?

Answer 1

http://en.wikipedia.org/wiki/Crystal_structure

it is because of the crystal structure

Answer 2

Sort of a tough question to answer online, but think of it this way.. crystals reflect the compounds in which they are made of, because the compounds fit togather in only a limited number of ways.
It's like if you took a bunch of leggo blocks...lets say you had 10 totally different shaped leggos... and the leggos would represent the molecules that you will combine to make a crystal.. well the overall shape of the final crystal would depend on the specific types of leggo's you used. Just like the shape of the crystal is influenced by the compounds that it is composed of.
Obviously it is more complicated than that... but that describes most of the variation