From the worksheet for insulators and conductors (http://www.allaboutcircuits.com/worksheets/candi.html):
"Q How much voltage can a 50 mm thick piece of mica withstand before breaking down?
A Approximately 1000 volts, or 1 kV. "
According to http://www.princeton.edu/~chaol/Rsch/Mica.html and http://www.sciencemadness.org/talk/files.php?pid=190313&aid=11801 the dielectric strength of Mica is much, much greater, around the order of 100kV per mm.
https://www.google.com/#
"Q How much voltage can a 50 mm thick piece of mica withstand before breaking down?
A Approximately 1000 volts, or 1 kV. "
According to http://www.princeton.edu/~chaol/Rsch/Mica.html and http://www.sciencemadness.org/talk/files.php?pid=190313&aid=11801 the dielectric strength of Mica is much, much greater, around the order of 100kV per mm.
https://www.google.com/#