That piece of stone could be anything including just being a piece of stone never seen before by anyone other than the self serving archeologist that is holding it.
Humanly-worked quartzite flake
There are unmistakable signs on a piece of quartz or flint when it has been worked.
Leaving a digital trail on the internet, was BEYOND stupid! That tells me they were planning on having no witnesses, and you know what that means for the home owner.
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My crescent wrench could have been a hunk of iron ore that fell into a volcano, melted, mixed with carbon, was erupted out and flowed into an obscure, wrench like depression in the ground, and became a weird, natural, wrench shaped rock. Works pretty good though.