Here is a list of collectibles (spoiler...don't look if you don't want to know them)

The Jet black crystal can be found on earth, I've dug one up many times in the course of normal excavating. If you want plants, especially early on in a sims life check out the garden at the Von Haunt Estate in Get Together. There are 16 different plants there with no waiting. Just get gardening skill to level 1 and be there at 5:30am.