I know purchasing artifacts isn't purpose of what you mean by educational, but if you want to buy slate artifacts, buy a grouping like that first and study, study, study them under magnification. There is a PhD authentic in slate right there.
There is so much to learn from handling broken examples like those, not limited to:
The details of workmanship
The drilling
The polish
The edge grinding
How holes are drilled from both sides on one type of gorget are drilled from one side on another style
Little areas of hafting polish on one side of the hole on some types of gorgets.
The type of drilling on broken butterfly banners
The cross section on different types of gorgets (some are flatter than others, some are domed, some have a trapezoid shape, etc.)
Different kinds of patina on different types of slate & shale.