Slate is a homogenous rock, fine grained and is easy to separate into layers. These rocks were formed from sediment or clayey pre-existent stones and metamorphosed under great pressure.
Slate splits naturally on its grain of cleavage into what we know as slate. The surface texture of the slate is influenced by the way it splits, the grain is not always visible to the naked eye.
The sedimentary rock that forms Quarry slate are made up of many minerals such quartz, muscovite, dolomite feldspar, calcite, pyrite & other carbonaceous substances. these mineral inclusions can be visible on the surface of a slate but should not go completely through. inclusions of pyrite should be of a cyrstallised stable form.