Emeralds and another gem, hiddenite, are found only in that area.    From Wordnik.com.  [CNN.com] Reference

Somebody got to my site searching for "is hiddenite mine a scam" - no, it's not, they are quite open about how they operate.    From Wordnik.com.  [Amanita.net] Reference

The accidental discovery some fifteen years ago of emerald and hiddenite in Alexander county, where gem mining on a considerable scale was conducted for several years, may be considered the beginning of this industry.    From Wordnik.com.  [North Carolina and its Resources.] Reference