Slate industry
In the remainder of Continental Europe and the Americas, Portugal, Italy, Germany, Brazil, the east coast of Newfoundland, the Slate Valley of Vermont, New York, Pennsylvania, and Virginia are important producing regions.
In Galicia, the larger slate production companies are concentrated in Valdeorras in Ourense, with other important sites being situated in Quiroga, Ortigueira and Mondoñedo.
The slate deposits in this region of northern Spain are over 500 million years old, having formed during the Palaeozoic period.
The region has been subjected to periods of volcanism and magmatic activity, leading to a unique geological development.
It is particularly suitable for this purpose as it has a low water absorption index of less than 0.4%, making it very resistant to frost damage and breakage due to freezing.
Hook fixing is especially prevalent in areas subject to severe climatic conditions, since there is a greater resistance to wind uplift as the lower edge of the slate is secured.
Welsh output was far ahead of other areas and by 1882, 92% of Britain's production was from Wales (451,000 t): the quarries at Penrhyn and Dinorwic produced half of this between them.
Half the partners worked the quarry face and the others were in the dressing sheds producing the finished slates.
In some mines, where slate was worked away below the main haulage floor, the route was maintained through the construction of a wooden bridge across the chamber, often supported from chains attached to the roof above.
These all worked a pair of slate veins that ran across the Cambrian mountain range from Tywyn in the west through Corris and Aberllefenni in the Dulas Valley to the mines around Dinas Mawddwy in the east.
Many of the mines are now in a state of considerable decay and those that are accessible should not be entered as they are on private property and contain many hidden dangers.
During the last 500 years, much slate extraction has taken place in the Lake District at both surface quarries and underground mines.
The Pennsylvania Historical and Museum Commission states that in the Slateford Water Gap area the first verified quarry started some time around 1808 .
The industry in this region of Pennsylvania spread across the northern edges of both Lehigh and Northampton counties which contain between them the remains of approximately 400 individual quarries.
The origins of quarrying in the Lehigh Valley are obscured by conflicting evidence, although it is safest to say that it started near the town of Slateford in the early Nineteenth Century and moved toward Bangor over a fifty-year period.
The slate of the region comes in a variety of colors, notably green, gray, black and red.
Their trademark Buckingham Slate has been continually quarried since the 18th century and has a distinct, unfading blue/black color and Mica sheen.
[11] The independent Fundación Centro Tecnológico de la Pizarra’s report into the ’Technical properties of Bambui Slate from the State of Minas Gerais (Brazil) to ascertain its compliance with the Standard EN12326’ describes how certain products originating from Brazil on sale in the UK, are not entitled to bear the CE mark.
Because such Brazilian products display higher water absorption indexes than those from other areas such as Galicia, this makes them less suitable for use as roofing tiles since the study showed a significant loss of strength when subject to thawing and freezing.
