From Jeff Daly    https://drive.google.com/?usp=chrome_app#folders/0B3335E19EZzTSG9TT0Jpdllycms

http://glassian.org/Prism/index.html
http://glassian.org/Prism/Vault/index.html

http://cyclotram.blogspot.com/2006/11/like-amethysts-beneath-my-feet.html

Cities 101: What are the Little Glass Circles in the Sidewalks of Soho?
http://untappedcities.com/2014/04/29/cities-101-what-are-the-little-glass-circles-in-the-sidewalks-of-soho/