Thin sheet of Muscovite Mica. (IMAGE) Shibaura Institute of Technology Caption Muscovite mica (MuM) is a layered mineral commonly used as an insulator. In a new study, researchers observed that, when thinned down to a few molecule layers, MuM acts more like a semiconductor with a thickness-dependent conductivity. Credit James St. John Usage Restrictions Credit must be given to the creator. License CC BY Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.