If it's the size of a last-generation sixpence (from the 1800s or 1900s), then it's not going to be a sixpence. Inflation caused all the silver coins to shrink over the past several hundred years. This coin is a rose-and-thistle "rosa sine spina" small crown halfgroat (twopence) of James I, I believe, like Sear #2660. In better condition, it looks like
this.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis