I feel like the best explanation to cover all their questions at once would be to come up with some fake story about being an inventor or experimenter and that (s)he's about to get a big breakthrough if (s)he can just get enough Crystals for it. It could explain why he looks weak and thin (too much time indoors experimenting), what (s)he needs a lot of a typically-undesirable material, and might be able to explain why (s)he has a lot of gems and other stuff. lol