Valentia Slate


Chimney at quarry site

Year designation



A penetratively cleaved, well compacted, fine grained siltstone, composed of quartz, muscovite and chlorite with minor opaques


Slate with a very consistent purple colour that is highly susceptible to a honed polish and which develops an excellent patina in areas of heavy use

Geological settings

Middle Devonian – Givetian – Iveragh Group – Valentia Slate Formation; Alluvial floodplain deposit


Dohilla, Valentia Island, Co. Kerry, southwest Ireland

Chimney at quarry site

A versatile paving and roofing slate

Valentia Slate was first extracted in large volume from 1816 from a quarry at Dohilla on Valentia Island, southwest Ireland, that was operated by the landlord Maurice Fitzgerald, the Knight of Kerry. From 1840 stone was extracted along strike from two underground chambers: the deepest is the ‘Grotto Chamber’, that penetrates 150 m into the hillside and is 20 m high. Stone was squared on site and then transported to a slate yard at Knightstown on the island for further splitting into slabs, approximately 2 m long by 25 mm thick, prior to their export by sea. At the height of production these operations employed over 200 men. Between 1911 and 1998 the quarries were idle, but since then extraction is ongoing. Valentia Slate is a very workable and durable stone, which has been put to many uses. Its strength and capability of being raised as slabs led to its application beyond simply that of roofing. It has been utilised on a global scale for paving, roof slates, monuments and in domestic and industrial applications. Throughout the nineteenth century the premier market for Valentia slabs was in the United Kingdom where the stone was adopted in particular to floor and roof industrial units, bonded warehouses, schools and prisons. It was also fabricated into cisterns for holding water or spirits, and skilfully carved as garden furniture and billiard tables. The stone was ideal for the latter on account of it being able to provide a very flat playing surface; some of these tables were decoratively enamelled in a process patented by George Magus, a one-time lessee of the quarry.

Slate workers cottages at Knightstown

Valentia Slate Quarry viewed from the southeast.

Patrick Wyse Jackson and Louise Caulfield.

Prof. Patrick Wyse Jackson, Department of Geology, Trinity College, Dublin 2, Ireland