Here's a seemingly simple question that I've wondered about even since I
saw it done in a geology class over 20 years ago. Why is it that when you
wet a rock, it becomes darker and more reflective?
I'm thinking it has to do with both reflection and refraction.
The water makes the rock reflect like a mirror as water is somewhat
reflective itself. And the water-rock interface has a smaller refractive
index difference (compared to air-rock) and is absorbed more (reflected
less) by the rock. I'm not exactly sure.