Which only leads to the question how did someone know this was a completely new mineral and name the mineral hiddenite?
It was the same guy that invented unobtainium.
Hiddenite was named after the geologist William Earl Hidden, and the North Carolina town was eventually renamed with the mineral’s name. There are a variety of criteria used to describe minerals, and when differences from currently-known minerals are observed, they say they’ve found a new mineral. X-ray crystallography is very useful, although they didn’t have that at the time hiddenite was identified!
I took a class from a geologist who had found a new mineral in Antarctica, which was the only place that particular compound was found in nature in a solid state.