According to Pliny, the emperor Domitian was so paranoid about his personal safety that he had the walls of his portico lined with phengite, so he could see who was walking behind him.
9.
Nero's Golden House was lined with plates made from a type of mica called phengite that, Seneca wrote, " gave off such a dazzling glow that they overpowered the natural light of day ."
10.
"' Phengite "'is a series name for dioctahedral micas of composition K ( AlMg ) 2 ( OH ) 2 ( SiAl ) 4 O 10, similar to muscovite but with addition of magnesium.