Is this normal or does it denote anything negative?
Water leaking
Horse PI$$ Ammonia storage of some chemicals will also do it.
Could there have been a cat litter box and lots of cats.
Chinese Dry wall
http://www.nachi.org/forum/f22/black-copper-cold-water-lines-2837/
Appears that maybe the sink wasn’t used often and maybe the interior seals dried a bit and then when you use the faucet they seep just a hair and this happens over a long period of time, this is what you get. Just look like a small amount of seepage over a long period of time.
Still a leak . I like short and sweet . I queses thats why i put up with Sean lolol
Your’e Gay…
Touch the crust and tell us what happens. 
Deposits are signs of leaks . Small but a leak just like on galvanized pipe.
I am assuming you meant on the Pipe LOL
BTW i was going to see if you wanted to meet for breakfast dippy
It is normal, it denotes leaking/Corrosion.
Need to be replaced
LOL and you call him gay.:mrgreen:
Two different metals. Electrolysis. Thats what it looks like. The fittings bought at same supplier.
Just a shot.