Mica is a silicate mineral that can be found in nature as metamorphic or igneous rocks. Mica can also be found in sedimentary rocks depending on the types of minerals left behind by water and what minerals are in the area.
When mica is classified, it is considered to have an almost perfect cleavage when it breaks. This can also be called a slaty cleavage, but either term basically means that the rock splits at parallel or planar surfaces and the minerals are so small that they cannot be seen by the naked eye. This gives them a smoother look when they break and makes it seem more like they have been cut.