What is this? Jewelry, button...?

[austinkirsh]

I was out metal detecting in my yard today and came across this. It's brass or copper and it has some type of stone or glass in it. The stone has a slight bevel on the edge. I just can't figure out what it might be. Any ideas?

 

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[Lafitte Deux]

It looks like machine part to me, maybe an indicator. Does the "stone" appear to be glass?
And is the metal tube in the back hollow? Also, diameter and thickness would help.

 

[austinkirsh]

I added a dime for size reference. The pin on the back is not hollow, and if you look closely at the back there are a few specs of a gold color. I'm not sure how I would tell the difference between glass and stone, but to me it looks like a stone. There are some tiny cracks around the outside of it, and there are a couple spots of yellow you can see mixed in with the red.