I like writing and I like science. While it can be a lot of fun to have fantasy worlds where the laws of physics are on vacation: Mars is actually a giant ruby! I also like to know more sound physics and chemistry answers: Mars isn't a giant ruby, it's covered in iron oxide. Please keep in mind that I'm new here and I haven't had time to look up all the answers to the questions below. If someone else has already asked them, please let me know and link me to that answer.
Mars is red because of the iron oxide. Presumably if it had copper oxide instead it might look green. What other chemicals could yield other colors such as purple or yellow or anything else on a solid surface. I know water can make blue and sulfur can make yellow, but I'm looking for something 'dry' for blue and I'm less sure about a planet with an entire surface made of sulfur.
In similar vein, I know methane causes the blues of Uranus and Neptune and sulfur causes yellows, but I again am not sure what other chemicals could be present in a gas giant/ice giant to produce red or purple or similar.
Thanks in advance anyone that answers!
*I have edited out my other questions and started posting them as separate threads, as was suggested by a couple people. I'm sorry for the confusion. Thanks to everyone that has answered so far!
Separate from the chemicals:
How might a "super-earth" have looked in the place of Venus or Mars?
If we had a hot Jupiter or hot Neptune, what might it have looked like?
If Venus had a moon relatively the same size as ours, when would it have been visible?
If a Mars-sized world circled another, larger, world in the orbit of Mars, would both have been visible for ancient people? What about Venus?
How long could two similarly sized planets rotate around a common barycenter?
If Earth had a second moon, how far out would it have to be to be stable over a relatively long time (say around 8 billion years or so)?
Would it have been possible for there to be three habitable Earth-sized worlds in our solar system, and if so where would they have to be placed?
Is it possible to have an Earth-like world circle a gas giant? If so, at what distance from the main planet? What might fellow orbiters look like? Could it have it's own moon?