Victor Cardenes has been working on a poster summarizing the main roofing slate outcrops in the World.
It compiles the location of the outcrops together with a new classification of roofing slates taking into account the color and the petrology.

For example, the lithotype B1 corresponds to the black-grey metamorphic slates, the most common type, while R1 would correspond to also metamorphic slates but with purple-red colors.
Source : Victor Cardenes - roofingslate.wordpress.com - November 2015
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