another application I could envision would be amateur prospecting. But smartphones know your location, so same problem.
So? The smart phone will report it's location at the time that you analyse your specimen. Which will probably be in the hotel/ motel that you go to when you get back to something resembling civilisation.
You think that you'll have a mobile phone signal out in the field at your prospect? Damned all chance of that, because mobile phone companies don't put transmission towers where they don't have customers, and if there are any significant numbers of people in an area then it has probably been gone over already by mineral prospectors.
I'm an amateur mountaineer and professional geologist. I don't normally have signal on my mobile when I'm out on the hill. Likewise when I do onshore jobs in the deserts of Arabia or the tundra of Russia. And when I'm 100km out at sea, again, no signal.
Look at this map ; get out into unpopulated areas and you've got little chance of getting a signal. If you're in a populated area, then it's almost certainly already been prospected.