DORSET BUILDING STONE
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Chert  (Lead Author: WGT)

 Chert is a dense, very hard, siliceous rock which occurs in the Upper Jurassic Portland Stone Formation, the Lower Cretaceous Lulworth Formation and the Mid-Cretaceous Upper Greensand Formation.  Flint (qv) is a similar Upper Cretaceous siliceous rock but is covered separately in this website.  In all cases the silica is biogenic, sourced by sponges and micro-organisms with a silica skeleton and, in most cases, the silica has replaced a host limestone. (see also Portland Stone section under Jurassic. Click HERE to go to the Jurassic main page)
Portland Stone Formation: This comprises the Portland Chert Member overlain by the Portland Freestone Member.  The former consists of grey shelly lime mudstones rich in calcite casts of marine sponge spicules (Rhaxella).  Grey chert occurs throughout in discontinuous patches and layers.  Chert also occurs in the Freestone Member as thin layers picking out cross-bedded ooid dunes and as patches in the highest levels. 
Picture
Chert preserving shells in the Portland Roach. Photo:WGT
Lulworth Formation:  The topmost level of the Worbarrow Tout Member is the “Cherty Freshwater Beds”, lacustrine bioclastic pelletal lime mudstones, with patches of chert.  In the Isle of Purbeck, vertebrate  bones and footprints are known from these beds.   This chert is not known to have been used as a building material. 
Picture
Forde Abbey. The monks’ dormitory is faced with chert from quarries within Thorncombe parish. Photo: WGT.
Picture
The ruined chapel at Stanton St. Gabriel was built with chert from Hardown Hill. Photo: JT.
Chert was quarried from all the hills around the Marshwood Vale, in particular from Hardown Hill, Morecombelake, where several open quarries were cut into the side of the hill and mines driven in from the upper level.  
Picture
Photo: WGT
Silicification took place during early burial and has preserved the shell structure of bivalves and gastropods which are usually seen as moulds (Portland screws).  Chert is also present  in the mainland outcrops from Durlston to Portesham.   It was never suitable as a building stone but is quarried and crushed on Portland for aggregate.  The chert was widely distributed in Mesolithic times for tool manufacture.
Picture
Chert from Hardown Hill. Photo: JT
Picture
South wall of Catherston Leweston Church Closely fitted knapped chert. Photo: JT.
Upper Greensand (qv):  Chert is common in certain members of the UGS and used widely as a building material, especially in West Dorset and SE Devon.  The UGS sediment ranges between marine calcareous sandstone and quartzose bioclastic limestone, usually fine to medium sand grade.  Biogenic silica has replaced the calcium carbonate and filled the pore space between sand grains, resulting in zero-porosity chert nodules.  These distinctive orange cherts have been used for walling as undressed rubble or knapped to form very durable close-fitted external surfaces.  UGS chert was used for tool-making throughout the Palaeolithic to Neolithic periods.
Picture
Charmouth Church with knapped rubble chert (R). Photo: WGT
WGT/JT Feb 2017
Picture

© DORSET BUILDING STONE
and contributors
  • Home
    • About Us
    • Glossary
    • References and Sources
    • Work in Progress
  • Building stones
    • How we study building stones
    • Palaeogene >
      • Heathstone
      • Sarsens
    • Cretaceous >
      • Chalk
      • Flint
      • Upper Greensand
      • Chert
      • Wealden
      • Purbeck >
        • Upper Purbeck (Purbeck Marble)
        • Upper Purbeck (Broken Shell Lst. aka Burr)
        • Middle Purbeck (Upper Building Stones)
        • Lower Purbeck (Cypris Freestones)
    • Jurassic >
      • Lower Purbeck >
        • Cypris Freestones
      • Portland Stone - Dorset
      • Chert
      • Kimmeridge Bay Dolomitic Limestone
      • Corallian
      • Cornbrash
      • Forest Marble
      • Fuller's Earth Rock
      • Inferior Oolite
      • Bridport Sands
      • Junction Bed
      • Blue Lias
    • Dorset Bricks
    • Non-Dorset Stone >
      • Tertiary >
        • Bembridge Limestones - Isle Of Wight
      • Cretaceous >
        • Beer Stone - SE Devon
      • Jurassic >
        • Bath Stone - Somerset & Wilts
        • Blue Lias of Somerset
        • Doulting Stone - Somerset
        • Ham Hill Stone - Somerset
        • Portland Limestone – Wilts (Chilmark)
        • Normandy >
          • Pierre de Caen (Caen Stone)
        • Pas de Calais
      • Triassic: White Lias of SE Devon
      • Carboniferous >
        • Carboniferous Limestones: Polished Black
      • Devonian
    • Building Stone Trails >
      • Devon Trails
      • Somerset Trails
    • Stone Index >
      • Stone Index A-B >
        • Abbotsbury Ironstone
        • Bath Stone
        • Beer Stone
        • Bembridge Stone
        • Binstead Stone
        • Blue Lias Stone
        • Bridport Sandstone
        • Broken Shell Limestone
        • Burr
        • Burton Limestone
      • Stone Index C-E >
        • Caen Stone
        • Carstone
        • Chert
        • Chilmark Lower Building Stone
        • Chilmark Main Building Stone
        • Chilmark Stone
        • Chilmark Upper Buiding Stone
        • Clavellata Beds
        • Cliff Stone
        • Clunch
        • Corallian
        • Cornbrash
        • Cypris Freestone
      • Stone Index F-O >
        • Featherbed Limestone
        • Featherstone
        • Forest Marble
        • Flint
        • Fuller's Earth Rock
        • Grey Chalk
        • Ham Hill Stone
        • Heathstone
        • Inferior Oolite
        • Ironstone
        • Lower Chalk
        • Lower Lias
        • Melbury Sandstone
        • Middle Chalk
        • Middle Lias
        • New Vein
        • Osmington Oolite
      • Stone Index P-T >
        • Portland Cherty Beds
        • Portland Cherty Series
        • Portland Stone
        • Purbeck Marble
        • Purbeck Stone
        • Quarr Stone
        • Rag
        • Sarsen Stone
        • Shaftesbury Sandstone
        • Sherborne Stone
        • Tisbury Stone
        • Todber Freestone
        • Trigonia Beds
      • Stone Index U-Z >
        • Upper Chalk
        • Wardour Lower Building Stone
        • Wardour Main Building Stone
        • Weald Clay
        • White Chalk
        • White Lias
        • Yeovil Stone
  • Churches
    • A-Z of Churches
    • East Dorset >
      • Almer
      • Bournemouth >
        • Talbot Village
      • Canford Magna Chapel
      • Corfe Mullen
      • Christchurch Priory
      • Cranborne
      • Edmondsham
      • Gussage All Saints
      • Gussage St. Andrew
      • Hampreston
      • Kinson
      • Knowlton
      • Morden
      • Pamphill
      • Poole St.James
      • Poole, the Spire Church
      • Shapwick
      • Sturminster Marshall
      • Tarrant Crawford
      • Tarrant Keyneston
      • West Parley
      • Wimborne St.Giles
      • Wimborne Minster Exterior Tour
      • Wimborne Minster Interior
      • Wimborne Minster: Purbeck Marble and Decorative Stone
    • Central Dorset >
      • Bloxworth
      • Bradford Peverell
      • Cerne Abbas
      • Hilton
      • Lytchett Matravers
      • Stratton
      • The Piddle Valley >
        • Affpuddle
        • Alton Pancras
        • Bere Regis
        • Piddlehinton
        • Piddletrenthide
        • Puddletown
        • Tolpuddle
      • Winterborne Tomson
    • North Dorset >
      • Batcombe
      • Belchalwell
      • Blandford Parish Church
      • Blandford St. Leonard's Chapel
      • Blandford St. Mary
      • Blandford Cemetery Chapels
      • Bradford Abbas
      • Chetnole
      • Child Okeford
      • Compton Abbas
      • Farnham
      • Folke
      • Gillingham
      • Hammoon
      • Hazelbury Bryan
      • Holnest
      • Ibberton
      • Iwerne Minster
      • Langton Long
      • Leigh
      • Mappowder
      • Margaret Marsh
      • Marnhull
      • Melbury Abbas
      • Melbury Bubb
      • Pimperne
      • Okeford Fitzpaine
      • Purse Caundle
      • Ryme Intrinseca
      • Shillingstone
      • Sixpenny Handley
      • Stockwood
      • Stourpaine
      • Tarrant Gunville
      • Tarrant Hinton
      • Tarrant Monkton
      • Tarrant Rushton
      • Todber
      • Winterborne Stickland
      • Winterborne Zelston
      • Woolland
      • Yetminster
    • South Dorset >
      • Abbotsbury
      • Bindon Abbey
      • Church Knowle
      • Coombe Keynes
      • East Holme
      • Kingston
      • Martinstown
      • Moreton
      • Portesham
      • Portland: Reforne
      • Steeple
      • Stinsford
      • Studland
      • Swanage
      • Upwey
      • Wareham St. Martin-on-the Walls
      • Wareham St.Mary >
        • St. Martin's-on-the-walls
      • Winterborne Came
      • Winterborne Steepleton
      • Wool
      • Worth Matravers
    • West Dorset >
      • Beaminster
      • Bothenhampton
      • Bradpole
      • Bridport
      • Broadwindsor
      • Burton Bradstock
      • Burstock
      • Catherston Leweston
      • Chelborough
      • Evershot
      • Eype
      • Loders
      • Monkton Wyld
      • Netherbury
      • North Poorton
      • Powerstock
      • St. Gabriel’s
      • Shipton Gorge
      • Lulworth Castle
      • Stoke Abbott
      • Symondsbury
      • Wootton Fitzpaine
      • Whitchurch Canonicorum
  • Quarries , Pits and Limekilns
    • Active Quarries
    • Abbotsbury area
    • Beacon Limestone Quarries
    • Inferior Oolite
    • North Dorset Corallian
    • Kimmeridge Bay
    • Portesham
    • Portland near Swanage
    • Purbeck near Swanage
    • Shaftesbury Sandstone
    • Uplyme Quarries
    • Upwey
    • Whiteway Hill Quarry
    • Winspit Quarry
    • Non-Dorset Quarries and Pits
  • Secular buildings
    • Athelhampton House
    • Blandford Town Hall
    • Cerne Abbas (village and Abbey)
    • Durweston Bridge
    • Ibberton Village
    • Kimmeridge Bay
    • Moignes Court
    • Non-Dorset Buildings
  • Search
  • Contact Us