Thanks in advance for sharing your expertise!
I believe that’s a Mexican “eagle” mark (1948-1980). You might be able to google “JC (or JL?) Mexico eagle 157” and see what you can find, but there are thousands of Mexican silversmiths, and I’ve not always had luck in identifiying makers. JC is probably their initials, and 157 i believe is their hallmark registration number.
I’ll let others weigh in on the stone. Nice old piece!
Thanks for the info and speedy reply!