Here's a breakdown of the key characteristics:
* Slate: Fine-grained, with a dull, smooth surface, and splits easily along flat planes.
* Phyllite: Has a slightly coarser grain size than slate, with a silky or sheen-like luster due to the presence of fine mica flakes. It still splits along planes but is less easily broken than slate.
* Schist: Has a distinctly coarser grain size than phyllite, with visible mica flakes and other minerals that create a more pronounced foliation.
Therefore, phyllite acts as a transition between the fine-grained, smooth slate and the coarser, more visibly foliated schist.
