The shiny black bits you can see in this piece of rock are Anthracite, which is a high quality coal. It's formed by fossilized plant material that would have washed down into the lagre delta area, that covered this place over 300 million years ago, and settled in the mud beds. While it is high quality we only find tiny seams like this locally.
County Clare

You can see more of her in action in "Aillte"
Episodes 1 and 2 of documentary now available for streaming on TG4.

https://www.tg4.ie/en/player/categories/top-documentaries/?series=Aillte&genre=Faisneis