Duh

If you are walking along the beach looking for pretty rocks and you see one that is interesting and you pick it up and look at it and say "Hmmm. This rock seems to have some sort of skin condition, eww! it has rock fungus on it. Ick" and then you throw it away. Rocks don't get "skin conditions". There is a name for that "condition", its called an AGATE! rocks don't grow "rock fungi", some rocks are agates.

I was walking along the beach and looking for rocks and a lady along the beach saw me and asked if I was looking for agates and I said "I don't know what an agate looks like" and she dug through her bucket and picked one out and I said "Oh, yeah, I found a couple of those but I thought they had a fungus on them. I threw them back". That made her sad. People collect agates, the sell agates, they collect agates to sell - they don't throw them away because they have skin conditions. I know that now.