Chemical Formula: KAl3Si3O10(OH)2
Color: Usually beige or brown
Importance: In the past, muscovite was used as windows due to its transparency. Today, it is used as an insulator due to its poor heat conduction and is also used in many cosmetics.
Other Interesting Information: Muscovite forms in thin sheets that layer on top of themselves to form the mineral specimens. This means that you can actually peel away layers of the mineral.
My Take: Although muscovite is one of the most common minerals, I still love it. Not only can you peel it away whenever you want, but you can even write things on it because it is so soft, which is very unique.
For More Information: http://www.minerals.net/mineral/muscovite.aspx