Tresayes Quarry is a nature reserve near

Roche F. Hoffmann-La Roche AG, commonly known as Roche (), is a Switzerland, Swiss multinational corporation, multinational holding healthcare company that operates worldwide under two divisions: Pharmaceuticals and Diagnostics. Its holding company, ...

Cornwall Cornwall (; or ) is a Ceremonial counties of England, ceremonial county in South West England. It is also one of the Celtic nations and the homeland of the Cornish people. The county is bordered by the Atlantic Ocean to the north and west, ...

. It is also a geological nature reserve of

Cornwall Wildlife Trust The Cornwall Wildlife Trust (founded as the Cornwall Naturalists' Club) is a charitable organisation founded in 1962 that is concerned solely with Cornwall, England, United Kingdom. It deals with the conservation and preservation of Cornwall's w ...

and is designated as a (non-statutory) County Geology Site. The entrance to the reserve has a small car park with a gate a
///graver.brimmed.caveman
There is a geology trail linking Roche Rock to Tresayes Quarry.

Geology

The quarry is notable for a granitic

pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic c ...

intruding

hornfels Hornfels is the group name for a set of Metamorphism#Contact .28thermal.29, contact metamorphic rocks that have been baked and hardened by the heat of Intrusive rock, intrusive igneous masses and have been rendered massive, hard, splintery, and in ...

, originally a sedimentary rock thermally metamorphosed by the St Austell

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

intrusion. The pegmatite is composed of

orthoclase Orthoclase, or orthoclase feldspar ( endmember formula K Al Si3 O8), is an important tectosilicate mineral which forms igneous rock. The name is from the Ancient Greek for "straight fracture", because its two cleavage planes are at right angles ...

feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

mica Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into fragile elastic plates. This characteristic is described as ''perfect basal cleavage''. Mica is co ...

, and minor

tourmaline Tourmaline ( ) is a crystalline silicate mineral, silicate mineral group in which boron is chemical compound, compounded with chemical element, elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone comes in a ...

and

cordierite Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present, and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: to . A high-tempera ...

. Associated with the pegmatites, rare elements, such as

niobium Niobium is a chemical element; it has chemical symbol, symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and Ductility, ductile transition metal. Pure niobium has a Mohs scale of mineral hardness, Mohs h ...

cerium Cerium is a chemical element; it has Chemical symbol, symbol Ce and atomic number 58. It is a hardness, soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it ...

and

beryllium Beryllium is a chemical element; it has Symbol (chemistry), symbol Be and atomic number 4. It is a steel-gray, hard, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with ...

also occur.

History

When the quarry was first opened in the late 19th century, it was a source of pure

, which was used in the

glass making Glass production involves two main methods – the float glass process that produces sheet glass, and glassblowing that produces bottles and other containers. It has been done in a variety of ways during the history of glass. Glass container pr ...

industry. The site was known locally as the Glass Mine or Polpuff. It closed for several years but reopened in 1917, during the

First World War World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...

, to provide feldspar for electrical

porcelain Porcelain (), also called china, is a ceramic material made by heating Industrial mineral, raw materials, generally including kaolinite, in a kiln to temperatures between . The greater strength and translucence of porcelain, relative to oth ...

with at least 50

bal maiden A bal maiden, from the Cornish language , a mine, and the English "maiden", a young or unmarried woman, was a female manual work, manual labourer working in the Mining in Cornwall and Devon, mining industries of Cornwall and western Devon, at t ...

s separating the feldspar. The bal maidens were laid off in 1921 but some of the survivors were interviewed in 1980 by John Tonkin, who lived in Roche. Since 2011 the quarry has been an EarthCache, visited by the geocaching community.

References

Nature reserves of the Cornwall Wildlife Trust Quarries in Cornwall {{Cornwall-geo-stub