I am an amateur geologist. I don't have much time for it these days, but it still interests me a little. As I travel around or watch TV etc. I tend to notice the geology around me as part of the scenery and interest of an area.
I created an animation about geology back on 2007- do take a look:
Birth of an Island
I realise now it is quite crude, but its still a reasonable summary of its subject. Maybe it there was interest I might make the second part.
I have a fairly substantial collection or minerals, rocks and fossils- largely from the British Cretaceous, but with other specimens from around the world
To respond to the question about opals- I think the most important thing about investing in stones is to ensure that they are genuine. If you have no way of verifiying them, then only buy from reputable sources.
Opals have a certain inherant value in that they are difficult to simulate effectively, but as a relatively obscure stone, the price may be at risk of falling if a single major new source opens up. They are a relatively soft gemstone and are usually sold as a doublet or triplet- if you don't know what that is, you are not ready to invest in them.
I make quizzes. If someone shows major effort and interest in this subject, I might make an animated quiz about geology one time, but I will need to see support on this as I have a lot of calls on my time.
Geology is an important and under-rated subject that should be a bigger part of school curiculum.
Come on, make this club happen!