Thank you for your information Clovis, prompted me to look a bit closer. The developed and undeveloped film base looks nearly black. When I sand the back some white dust comes off but the base remains black in both the developed and undeveloped film. The emulsion looks a bit more tan than gray. A bit of undeveloped film put in fix slowly lightens a little and becomes slightly translucent but only to very bright light, nothing like BW film that goes clear.
So, likely some kind of color film? Transparency or negative?