Slate and water are the iconic exports of North Wales, reflecting the basic human need for shelter and sustenance. Roman sites prove that they used slate roofing on their local forts and villas as an alternative to fired, clay-based tiles.
Slate is known to have been used from the Dark Ages for local needs, but transporting a heavy commodity prevented its wider use and trade.
From the 13th century the use of slate expanded with the use of local material in high-status buildings and the major fortification projects of King Edward I, and sea-borne transport became established.
Slate Cottage, Pen-y-Groes, North Wales
The Industrial Revolution made transport and export of slates possible and production boomed.
In the late Victorian era exports reached 54,000 tons per annum, but there was competition from France and Spain, even within the UK. At this peak around 500,000 tons of finished slate was produced per annum, but decline continued almost continuously thereafter until it reached 22,000 tons in 1970.
Production for roofing is even smaller today, but architectural demand and the use of crushed slate for landscaping and granular fill makes total production almost 1M tons, much of which is from historic wastes.
Studying very fine-grained material such as mudstone or slate is difficult by conventional petrography.
No such problem attends the use of X-ray diffraction which relies upon fine powders for success.
Simple preparation enables rapid results, and the application of software methods of analysis (e.g. Rietveld), gives robust quantification.
Differences in mineral components highlight variation between Cambrian and Ordovician slates.
Analysis of many samples from various quarries shows systematic trends, but we have not yet included Silurian (or Devonian) examples in our work.
Further, details of the chemistry of component minerals (e.g. chlorite and mica) can be elucidated by examining the multiple peaks of their diffraction patterns.
X-ray fluorescence gives rapid and accurate chemical analysis, for spotting diagenetic changes in the bulk of the rock.
Data quality is regularly checked by participation in inter-laboratory proficiency tests and competitions. Click for more details.