What's my pool surface made of?

I've lived in my current house for three years and have an in ground pool. But I've never tried to figure out what the surface is (vinyl,fiberglass,concrete).

I'll be moving to a new place in a couple weeks with an in ground pool and I'd like to figure out what that surface is made of too.

Both pools are filled, is there a test or can it be determined by visual inspection and touch?

Thanks!
 

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