Here is a nice Pyrite - Trilobite plate  Ordovician of England with a positive and two smaler negatives as well.  The fossils are lightly preserved in pyrite that provides this trilobite its glossy golden metal look.
When these fossils are been found the pyrite is not shiny like nearly all Pyrite - Fossils. 
So also this trilobite got carefully a light polish to expose the golden pyrite when it got prepared.

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