what are slate and shale?
(This contrasts dramatically with GRANIREX, which is 93% natural Quartz). 4) Slate is metamorphic rock, like the marble. However, instead of forming from a pre-existing limestone (like marble), slate is formed from the low-grade metamorphism of the sedimentary rock shale. Slate, like shale (mudstone), is a very fined-grained rock of mostly microscopic clay minerals with some microscopic quartz and calcite.