What kind of Sapphire Crystal is used in watches

It does not really matter, since both natural and synthetic sapphire crystals are chemically and physically the same material -  it's pure aluminium oxide that has gone through a process of crystallization. The synthetic sapphire is as hard as the natural one. The watch industry uses almost exclusively industrially grown sapphire crystals, though, so I guess it is the same case at Garmin.

Yea, I guess, but I was curious what it is in this case. 

I'd tell that there is 99.999% probability of using the industrial sapphire crystal, just like at any other manufacturer producing watches in bigger series