Burgos, Spain, 1 real, Ferdinand-Isabel (pre-1497 type), rare, with unidentified (unique) countermark X-dot-dot-dot on obverse. CT-283. 2.76 grams. Host coin XF with full (Gothic) legends and inner details (rare early type struck prior to the Pragmatica of 1497, with arms of Castile and Leon on obverse and arms of Aragon and Naples/Sicily on reverse), bold countermark of X in one box and three dots in another to left of crowned shield on reverse, very similar to markings we see on gold ingots (on which this would represent 10-3/4 karats) but with nothing like it on any other coins known to us.
Estimate: $500-1000