I like rocks, in general, maybe because they're old and they just sit there, being all rock-ish and stony. In particular though, I think that all igneous and metamorphic rocks are cool, and that all sedimentary rocks are so-so at best. In order to be cool, sedimentary rocks have to be formed into something by erosion, like a limestone cave or the grand canyon or those big pillars in monument valley. Igneous and metamorphic rocks, on the other hand, do a fine job of standing on their own without having to be part of a landmark. Someday, I hope I can own some obelisks, and when I do, they will all be igneous or metamorphic.