I somehow have the half Kreuzer coin in silver in mind, google it
Sondelreise 21.9.2024
The one from 1858
SondelSuechtig 21.9.2024
I recognize a crown. There is probably a monogram underneath. It is not 4 or 6 pfennigs. The diameter does not fit. Maybe 1/12 or 1/24 thaler. My gut feeling is that I would look in the direction of Hanover or Braunschweig. You could possibly get more out of it by dry cleaning it.