Question: Which is the most colorful rock that you have ever found? And where? Can you explain why it has those colors?

Colours in rocks are always related with the chemistry. Blueschists are blue because of the mineral glaucophane. Serpentinites are blue because of the serpentine. The most colourful rocks I have seen are skarn deposits, that happen in the contact of granites with limestones. Usually they produce a lot of different minerals, and in very small areas you can see deep blue, green, turquoise , red, orange, yellow, purple…