Slate is a low-grade pelitic metamorphic rock. It is distinguished from higher grade grade phyllite by having a lower proportion of newly crystallised minerals, and accordingly, a lower sheen on the cleavage surface. Conversely, slate also contains a high proportion of the original sedimentary components such as silt and clay. Unlike shale, the layering present here is not sedimentary in origin, but tectonic. Growth of new phyllosilicates such as muscovite and chlorite creating a planar structure in the rock. Note that these metamorphic minerals are still too small to be seen with the naked eye.