Dee's scrying stone

[Coma of Loss]

In the foreword of the Skinner edition of TFR he suggests that Dee mentions (doesn't give a source though) the scrying stone being "a natural diaphanite" which I found very strange since "diaphanite" as a word describing a mineral didn't exist until the 1800's. At least the only reference I could find was the first suggested name for alexandrite.

http://www.alexandrite.net/chapters/chapter2/index.html

Maybe diaphanite was in Dee's time used to refer to color-changing stones in general?

diaphanite - from the Greek "di" - two and "aphanes", - unseen or "phan", to appear, or show