What does MCA stand for?

Mica

Mica is a mineral which is found in layered structure normally founds in granite and other rocks or in crystal. It is a good electrical insulator and used as a thermal insulator. A transparent, flaky mineral which splits into thin sheets and has excellent insulating and heat resisting properties, consisting of orthosilicates of aluminum or potassium; occurs naturally. Any of a group of mineral silicates crystallizing in monoclinic forms that readily separate into very thin leaves.