"Acid" and "Felsic" are basically the same thing. Rocks with a large amount of silica. I believe the term "acid" comes from the old belief that silicic acid was involved with granites and ryholites. It's a bad term and often confusing. But it really has nothing to do with acid.

You may also see mafic rocks described as "basic".

I'd be really surprised to see felsic rocks on Mars, it'd take some explaining. For felsic rocks to form, you need some sort of plate-tectonics going on.

If you want to know more, look into the various theories on how the earth's felsic crust formed during the Archean and the origins of granites in general. If I see a good site, I'll pass it on.

jms