Here is a great reference article: http://www.williamhenry.net/2017/04/there-is-a-light-being-within/

As usual, I should have these stones available for sale when you visit me in Virginia.

Next Wednesday I will be presenting at the above University Museum at 7PM. It is located at 518 West Main Street, just a few minutes walk from here, in Waynesboro! Check out their web-site at http://www.philosophy.org for a true treasure-trove.