How well does a granite headstone tombstone hold up over time?

I prefer a good granite over marble. Marble collects algae and if someone isn't around to clean it up every now and then it gets to looking terrible. Have you seen the old marble military markers? If there isn't an organization around to keep them clean, you can hardly read the names. They can be cleaned with a mixture of clorox and water and look new again but relatives who remember them die off and they get neglected.