There are several types of mica and mica products available to crafters. These are the basic types I found available online, and a way they can be used for crafting.

• Mica powder - comes in many colors, used as a pigment, adds sparkle. Mix with resin to color and add sparkle, sprinkle on glue like glitter, mix with acrylic paints and mediums, mix into soaps and candles - any time glitter would be used, pretty much. Also used in cosmetics such as eyeshadow to add shimmer.
• Mica flakes - from what I can tell, mostly used as fake snow, or as glitter when the desired effect is more rustic than fine glitter.
• Composite mica - lots of small pieces of mice bonded together, can be used in paper crafts to add sparkle by covering an image with a thin layer.
• Sheet mica (also called mica tiles) - thin layers of almost clear mica can be peeled off, used in a similar manner to plastic transparencies. Can be stamped on, painted, transfer images to it, etc.