www.925-1000.com

This necklace is so amazing, it has to be by somebody interesting. Marked twice. Thanks for your input! http://members.cox.net/flowbluebowl/feb3/mm01.jpg" onclick="window.open(this.href);return false;
http://members.cox.net/flowbluebowl/feb3/mm02.jpg" onclick="window.open(this.href);return false;
http://members.cox.net/flowbluebowl/feb3/mm03.jpg" onclick="window.open(this.href);return false;
http://members.cox.net/flowbluebowl/feb3/mm04.jpg" onclick="window.open(this.href);return false;

Can't see the mark very well. Best I can do is offer a possible lead for you to research.
There was a jewelry manufacturer who used a J in a triangle mark. Not sure if that's what you have there. R.M. Jordan & Company, Providence, Rhode Island. Started producing high quality jewelry about 1942. Not in business very long, at least through the 1940's. Highly sought after pieces.

Regards,
Pat.