Welsh Slate
Once shipped all over the world, Welsh Slate is a fine-grained, homogeneous, metamorphic rock which was derived from an original sedimentary rock composed of clay or volcanic ash through low grade regional metamorphism. The result is a foliated rock in which the foliation may not correspond to the original sedimentary layering.

Slate is mainly composed of quartz and muscovite or illite, often along with biotite, chlorite, hematite, and pyrite along with, less frequently, apatite, graphite, kaolin, magnetite, tourmaline, or zircon.

Slate can be made into roofing slates because it has two lines of breakability: cleavage and grain. This makes it possible to split slate into thin sheets. Fine slate can also be used as a whetstone to hone knives. In 18th and 19th century schools slate was extensively used for blackboards and individual writing slates.

Those quarries still producing slate today use techniques and machinery very different from those of yesteryear. Modern quarrying is a brutal process using large machines and large amounts of explosives.  Such techniques are necessary to ensure the industry's survival in a worldwide market place.  Alfred MacAlpine Slate are now the dominant force in the industry operating at Penrhyn, Oakeley, Cwt y Bugail and Penyrorsedd Quarries.
 

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