How to tarnish marcasite

Mind you, I am superb as a medical transcriber, but as a housewife, that is a completely different story. I was using a commercial silver cleaner to clean my husbands expensive sterling jewelry. I, being not as bright as the sterling, was wearing marcasite at the time and forgot to take it off. My marcasite is now as shiny as the sterling and it looks really ugly. How can I turn marcasite back to beautiful blackish finish it had originally? Please save me from the laughter of my teenage children and help me get the smug smile off of my husbands face by showing him I did not permanently ruin the beautiful marcasite gifts he has given me over the past 25 years. Thank you, Freya

The polish removed the oxidation film from the surface of the mineral (caused by a reaction with the sulfur ⇦ on eBay or Amazon [affil link] present).

Nothing you can do to safely return the original finish (possibility of damaging the mineral). It will regain it's color over time due to natural oxidation processes.