What is your OC's name/gem?: Tanzanite
What is/would be their favorite candy?: They really don't eat, so hard to say. X3
What do they think about trees?: Tanzanite is amazed, wonderstruck even and often finds them best place for meditation.
Have they ever been part of a gem war?: Tanzanite's are not built for fighting, they are messengers and diplomats. So while Tanzanite was there for the war, they technically where not a part of it.
What animal would they shapeshift to when in danger?: Egret, more then likely. Any sort of bird, though something a little more long legged or large wings.
My other OC gems are not as thought out, so I won't be including them. Though I have a Quartz, Tourmaline, and Moss Agate to name the one's I can think of off the top of my head.
And Little Dipper, here is some interesting tutorials for any help on making a Gemsona or Gem OC:
http://thecreatorofworlds.tumblr.com/post/112455115726/designing-a-gemsonahttp://thecreatorofworlds.tumblr.com/post/123999148566/gemsona-process-the-making-of-star-sunstone