Slate is a rock that forms from the low-grade metamorphism of the sedimentary rock shale. The alteration of shale by heat and pressure produces the pronounced partings that give slate its layered characteristics. The wild range in colors found in some slates, are the results of the stone being exposed to the different atmospheric elements allowing them to oxidize or rust.
Gauged/Calibrated: Refers to the square and uniform thickness of the tile. Although a gauged slate product will never be as completely uniform as a tile product, it will limit the variation thickness found within the series.
Ungauged/Uncalibrated: Products of this type do not have the consistent characteristics of gauged or calibrated. This does not mean there are no tolerances. Usually the tolerance is no more than ½”. This simply provides a natural look.