Dr. John Dee’s obsidian Scrying Stone, through which he and Edward Kelly communicated with angels. These communications were the foundation for Dee’s system of Enochian magic. I saw this in the Yale Center for British Art, as part of an exhibit of Horace Walpole’s collection at Strawberry Hill, which was Walpole’s home and the first construction of the gothic revival. (Walpole also wrote the first gothic novel, The Castle of Otranto, published in 1764.) Seeing this legendary mirror gave me shivers of joy and wonder.
“The mirror, made of highly-polished obsidian (volcanic glass), was one of many Mexica cult objects and treasures brought to Europe after the conquest of Mexico by Cortés between 1527 and 1530. Mirrors were associated with Tezcatlipoca, the Mexica god of rulers, warriors and sorcerers, whose name can be translated as ‘Smoking Mirror’. Mexica priests used mirrrors for divination and conjuring up visions.”
http://www.britishmuseum.org/explore/highlights/highlight_objects/pe_mla/d/dr_dees_mirror.aspx