Slate rock or slate stone originates from thin silt stratification, has a relatively light weight and is mainly composed of slabs, which offer large smooth surfaces (very useful for laying eggs of some species) and has a very elegant and useful shape.
The color is very dark, usually black or dark green, with some white veins. Slate has the characteristic of not releasing carbonates and therefore will not alter the water values, so it can be used in large quantity in the composition of the layout.