river rock as decorative border in bathroom shower

I am in the process of choosing materials for remodel.
I found some river rock I would love to use. My question is two part.
1) recommended? Since I am concern overtime mildew, soap, or even green moss? Might grow on them?

If yes, any good sealant that would prevent the above from happening?

2) Are all procelin tiles the same? I saw some tiles that is made in italy and I want to know about materialwise is it same as other procelins?

Thanks,
Monkey

Riverrocks of the tile venue type come two ways. One is a natural round-top look and the other is a flat-top look. The flat stones are in my opinion the only way to go. The round tops tho they appear more natural are hard to grout, hard to keep clean, and hard on bare feet. They also allow water puddles to remain on the shower floor and don't provide for sufficient drainage.