Crystal is well this is a big question not much is known about crystal, The first thing in the anime there is only one person who can use it which Guren. But even then we don't know much about her, what clan she is from, or what elements she uses to make it.
So what we can gather about crystal is that it is made from earth as both Kakashi and Kiba managed to use a lighting technique to destroy it, so earth is a element used but the other or others are unknown. Crystal strengths are: Strong against wood, water, earth, but crystal is weak against sound and lighting.
I would compare crystal to wood as it basically can do similar things it can: using your own body make solid structures out of them quickly like spikes etc. you a use both to help you manipulate the environment better to your advantage as the opponent may not have access to either of them.
yes I understand the template you may move on if you wish ^^