Abstract Arising mainly from its exceptionally varied suites of igneous and sedimentary rocks, Cornwall has a rich variety of building and decorative stones that were extensively exploited, both for local use and for export, before concrete and brick came to dominate construction in the twentieth century. Many of the types of building stone, such as elvan and sandrock, do not occur outside Cornwall, so local stone provides much character to the local built environment. Granites were extensively worked in the eastern part of the Carnmenellis Granite (mainly in Mabe parish), in the St Austell Granite (Luxulyan, Carn Grey and the china stone areas) and on Bodmin Moor (De Lank, Hantergantick, Cheesewring, etc.), as well as in the Kit Hill, Tregonning and Land's End granite masses. The predominant type used was the ‘coarse grained megacrystic biotite granite – smaller megacryst variant’ of Hawkes & Dangerfield. A significant trade in granite developed in the nineteenth and early twentieth centuries, employing large numbers of skilled quarrymen. Finished granite was exported all over the world; many iconic buildings in London and other major cities use Cornish granite. A tourmalinized granite, luxullianite, was an important decorative stone, and was used for the Duke of Wellington's sarcophagus in St Paul's Cathedral. Schorl rock is often found in older buildings in the granite areas. Most pre-nineteenth century granite building did not use quarried stone but used ‘moorstone’ obtained from boulders lying on the surface of the granite uplands. Large quantities of ‘minestone’ have been used in vernacular buildings, past and present, and in some medieval churches, sourced from the waste tips of metalliferous (both alluvial and vein operations) and china clay workings. Allied to the granites are the fine-grained elvans of granitic composition, usually intruded in the form of dykes. Greisening often improves the durability of elvans, which have been extensively used in some of the finest stone buildings in Cornwall, such as St Austell church tower, Antony House (NT), Trelowarren, Place (Fowey) and the Georgian buildings of Lemon Street, Truro. The best-known elvan quarries were at Pentewan, which yielded a freestone capable of fine carving. However, not all buildings described by architectural historians as being of Pentewan Stone came from Pentewan. Another important elvan was Newham Stone, widely used in the older buildings in Truro. Tremore elvan was used, together with luxullianite, mainly as a polished decorative stone to line Porphyry Hall at Place in Fowey and in other high-status buildings. Basic igneous rocks include an Upper Devonian metadolerite at Cataclews Point, west of Padstow, which provided the extremely durable Cataclews Stone, used from medieval times onwards for fonts and church carvings in the area around the Camel estuary. A more unusual stone, produced by carbonatization of an ultrabasic intrusion, is Polyphant Stone, mainly used for interior use and by sculptors, composed of a mixture of talc, chlorite, and various calcium and magnesium carbonates. The Polyphant Quarry was recently reopened to supply stone for the rebuilding of Newquay parish church and to supply stone for sculpting. Allied to Polyphant Stone is Duporth Stone, obtained from the cliffs of Duporth Bay, south of St Austell, which was used in the pillars of Truro Cathedral. Basic hyaloclastite was the main stone used in the great Norman Church of St German's in SE Cornwall. The Lizard ophiolite complex provided a source of serpentine for building and for the manufacture of polished slabs; ornaments made from serpentine are still produced. Slaty mudstones and sandstones of Devonian and Carboniferous age have been extensively used for traditional buildings throughout Cornwall, nowadays much slaty mudstone is still used for building and for Cornish hedge building. The Upper Devonian Delabole Slate Quarry has yielded high-quality roofing slate from Tudor times onwards but there are many other large active and disused roofing slate quarries in the Tintagel area and elsewhere in Cornwall, such as the underground slate workings at Carnglaze, now a tourist attraction and concert venue. Devonian sandstones, usually of turbiditic origin, are widely used for vernacular building in south Cornwall, and Upper Carboniferous turbidite sandstones are used in north Cornwall. The geologically youngest building stone, seen in the Newquay and Padstow areas, is a cemented bioclastic Quaternary beach sand, laid down at a time of high sea level during an interglacial as a raised beach. It is known locally as ‘sandrock’ but is a relatively weak building stone. St Carantoc's Church at Crantock and St Piran's Church on Perran sands were largely built of it. Supplementary material: A more detailed review of the various granite and elvan quarries that have been worked in Cornwall is available at http://www.geolsoc.org.uk/SUP18675 .

Abstract The Variscan granite batholith of Devon and Cornwall is host to extensive deposits of primary kaolin, known in Britain as china clay, which support an industry supplying over 3 million t.p.a. of product. This is the principal source of kaolin for W. European paper and ceramic markets. The genesis of these deposits took place in six stages. The initial stage was the intrusion of the main batholith at 290 Ma, a S-type biotite granite rich in heat producing radioelements; followed by limited Sn/W mineralisation (Stage 2). Stage 3a was the intrusion of an evolved Li-B-F rich magma at 270 Ma., low in colouring elements (Fe, Ti), which only reached the upper surface of the batholith in a significant way in the western part of the St. Austell granite intrusion, but probably underlies the batholith throughout most of its length. This was accompanied by the mainstage hydrothermal Sn/Cu mineralisation and associated greisenisation and tourmalinisation (Stage 3b). Intrusions of felsitic dykes (elvans) brought this episode to a close (Stage 3c). The ensuing Stage 4 cross-course mineralisation involved saline, lower temperature fluids without boron, and radiogenically driven convective circulation became the dominant hydrothermal mechanism. Argillation followed permeable zones established by tectonism and earlier hydrothermal activity. Because of the saline nature of the fluids, the clay mineral assemblage was dominated by smectite and illite, with only limited amounts of kaolinite. Flushing of the system by meteoric water, following the transition to a wetter climate in the Mesozoic allowed pervasive circulation of warm fresh water, which converted the clay minerals and feldspars to the kaolinite dominated assemblage we see today (Stage 5). Continuous solution and recrystallisation of the kaolinite led to leaching of colouring oxides and a steady increase in lattice order. Large authigenic curled stacks of kaolinite also formed in the matrix. Stage 5 merged into Stage 6, which is the deep weathering in Mesozoic and early Tertiary times which affected much of Europe. There is evidence that convective circulation and kaolinisation are still proceeding slowly today. Fortunately erosion has not stripped too much of the soft kaolinised granite away and the deposits, as seen today take the form of funnels or tabular (on edge) bodies with depths exceeding 200m in places. Most of the worthwhile china clay deposits are in or close to the intrusions of the Stage 3 lithium mica granite, notably in the western part of the St. Austell granite and the south-western edge of the Dartmoor granite.