Gemstone found in slate, would like identification of it

[SuperCid]

Need to get help to identify this stone!!!
I was examining some slate my father sent me and found this gemstone embedded in one of the pieces. However I cannot for the life of me figure out what this stone is. Please help identify it so I will know what I've got.

 

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[Eu_citzen]

Probably Pyrite, not a gemstone, though.

 

[loco oro]

Definitely pyrite, Pennsylvania blue slate from south east pa has pyrite inbeded throughout

 

[stdenis_jd]

Definitely pyrite, Pennsylvania blue slate from south east pa has pyrite inbeded throughout

2nd this^^

just to confirm, do a streak test. Should be gray/black. If it's anything other than that, let us know.