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Downrow Quarry, Bishop's Tawton, North Devon, Devon, England, UKi
Regional Level Types
Downrow QuarryQuarry
Bishop's Tawton- not defined -
North Devon- not defined -
DevonCounty
EnglandConstituent Country
UKCountry

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Collecting phosphate minerals at Downrow Quarry

Downrow Quarry, Bishop's Tawton, North Devon, Devon, England, UK
Cacoxenite etc. plate as removed from the quarry wall.

Downrow Quarry, Bishop's Tawton, North Devon, Devon, England, UK
Latitude & Longitude (WGS84): 51° 2' 47'' North , 4° 1' 23'' West
Latitude & Longitude (decimal): 51.04663,-4.02311
GeoHash:G#: gcj4kky2n
Locality type:Quarry
Köppen climate type:Cfb : Temperate oceanic climate
Nearest Settlements:
PlacePopulationDistance
Swimbridge669 (2018)3.7km
Barnstaple31,616 (2018)4.5km
Goodleigh450 (2018)5.0km
Chittlehampton239 (2018)6.6km
Fremington4,310 (2018)8.3km


This small, private quarry, occasionally worked for aggregates lies in the uppermost unit of the Codden Hill Cherts. The rock here varies between friable and moderately competent, and is intensely fractured.

The largely carbonate depleted mud and siltstones contain occasional fossils and frequent, lenticular phosphatic nodules (presumably coprolites comprising mainly fish bones and chitin) many of which have undergone variable dissolution.

The rock is variously stained with red, yellow and brown iron oxides/hydroxides; dendritic manganese minerals are frequent. In parts, the quarry exhibits very local and intense phosphate mineralisation.

The quarry is occasionally worked for aggregate. The farmer who owns the quarry lives nearby and he will ask anyone who has not asked permission to leave.

Regions containing this locality

Eurasian PlateTectonic Plate
EuropeContinent
British IslesGroup of Islands
Devon and Cornwall metalliferous mining district, England, UKMining District

Select Mineral List Type

Standard Detailed Strunz Dana Chemical Elements

Mineral List


8 valid minerals.

Rock Types Recorded

Note: this is a very new system on mindat.org and data is currently VERY limited. Please bear with us while we work towards adding this information!

Select Rock List Type

Alphabetical List Tree Diagram

Detailed Mineral List:

Cacoxenite
Formula: Fe3+24AlO6(PO4)17(OH)12 · 75H2O
Habit: massive, botryoidal, encrusting
Colour: yellow
Description: Cacoxenite is found as a bright yellow encrustation in fractures in the rock of the quarry, often in association with porous quartz veins. Where it is found, it is locally abundant but is absent through most of the quarry. Larger plates showing the phosphatic mineralisation vary across the suface between clove-brown and bright yellow, occasionally to orange and red. The cacoxenite is generally between a deep yellow-brown and bright yellow.
Reference: Alysson Rowan Collection
Eleonorite ?
Formula: Fe3+6(PO4)4O(OH)4 · 6H2O
Habit: Massive, bladed masses.
Colour: reddish-brown to clove brown
Description: Some reddish-brown areas of a small number of specimens show the bladed forms resembling those of eleonorite. Further work is required for confirmation.
Reference: Alysson Rowan Collection
'Manganese Oxides'
Reference: Alysson Rowan Collection
'Manganese Oxides var: Manganese Dendrites'
Habit: Dendritic - coarsely crystalline to lacy dendritic encrustations.
Colour: Black
Description: The development of manganese dendrites is particularly varied in this quarry - ranging from coarse, tangible crystals infilling fracture voids down to delicate, mossy developments across the siltstone surfaces. In places, these developments do present a particular aesthetic appeal.
Reference: Alysson Rowan Collection
Metavivianite ?
Formula: Fe2+Fe3+2(PO4)2(OH)2 · 6H2O
Habit: blased masses
Colour: dark green
Description: A few areas of phosphatic encrustation show the colour and approximate form of metavivianite. Further work is required.
Reference: Alysson Rowan Collection
Opal
Formula: SiO2 · nH2O
Reference: Alysson Rowan Collection
Opal var: Common Opal
Formula: SiO2 · nH2O
Habit: none: massive
Colour: white to off-white
Fluorescence: none
Description: Redeposited silica tubes formed in cracks in the Codden Hill Cherts which host a number of phosphate species. These thin-walled tubes appear to have formed in much the same way as speleothem 'straws', and various walls and ramifications appear across the rock surfaces. These same cracks also play host to the various phosphate minerals found at this location.
Reference: Alysson Rowan Collection
Rockbridgeite ?
Formula: Fe2+Fe3+4(PO4)3(OH)5
Reference: Alysson Rowan Collection
Strengite ?
Formula: FePO4 · 2H2O
Habit: botryoidal, encrusting; massive
Colour: pale purple
Description: Areas of purple phosphatic encrustations strongly resemble strengite.
Reference: Alysson Rowan Collection
Variscite ?
Formula: AlPO4 · 2H2O
Habit: botryoidal; encrusting
Colour: white
Description: Tiny, pale hemispheres and white encrustations have been tentatively placed as variscite. Variscite has been previously reported (unconfirmed) from this location.
Reference: Alysson Rowan Collection
Wavellite
Formula: Al3(PO4)2(OH,F)3 · 5H2O
Habit: Radial hemispheres, botryoidal
Colour: bottle green to black
Description: Small clusters of generally dark hemispheres lining a cavity formerly filled with phosphatic clay. Other minerals peresent in this specimen are manganese oxides, cacoxenite and other unidentified (phosphate) minerals. The specimen was removed in the process of extracting cacoxenite plates from the quarry wall.
Reference: Alysson Rowan Collection

List of minerals arranged by Strunz 10th Edition classification

Group 4 - Oxides and Hydroxides
Opal4.DA.10SiO2 · nH2O
var: Common Opal4.DA.10SiO2 · nH2O
Group 8 - Phosphates, Arsenates and Vanadates
Cacoxenite8.DC.40Fe3+24AlO6(PO4)17(OH)12 · 75H2O
Metavivianite ?8.DC.25Fe2+Fe3+2(PO4)2(OH)2 · 6H2O
Rockbridgeite ?8.BC.10Fe2+Fe3+4(PO4)3(OH)5
Strengite ?8.CD.10FePO4 · 2H2O
Variscite ?8.CD.10AlPO4 · 2H2O
Wavellite8.DC.50Al3(PO4)2(OH,F)3 · 5H2O
Unclassified Minerals, Rocks, etc.
Eleonorite ?-Fe3+6(PO4)4O(OH)4 · 6H2O
'Manganese Oxides'-
'var: Manganese Dendrites'-

List of minerals arranged by Dana 8th Edition classification

Group 40 - HYDRATED NORMAL PHOSPHATES,ARSENATES AND VANADATES
(AB)5(XO4)2·xH2O
Strengite ?40.4.1.2FePO4 · 2H2O
Variscite ?40.4.1.1AlPO4 · 2H2O
Metavivianite ?40.11.9.4Fe2+Fe3+2(PO4)2(OH)2 · 6H2O
Group 41 - ANHYDROUS PHOSPHATES, ETC.CONTAINING HYDROXYL OR HALOGEN
(AB)5(XO4)3Zq
Rockbridgeite ?41.9.2.1Fe2+Fe3+4(PO4)3(OH)5
Group 42 - HYDRATED PHOSPHATES, ETC.CONTAINING HYDROXYL OR HALOGEN
A3(XO4)2Zq·xH2O
Wavellite42.10.2.1Al3(PO4)2(OH,F)3 · 5H2O
Miscellaneous
Cacoxenite42.13.5.1Fe3+24AlO6(PO4)17(OH)12 · 75H2O
Group 75 - TECTOSILICATES Si Tetrahedral Frameworks
Si Tetrahedral Frameworks - SiO2 with H2O and organics
Opal75.2.1.1SiO2 · nH2O
Unclassified Minerals, Mixtures, etc.
Eleonorite ?-Fe3+6(PO4)4O(OH)4 · 6H2O
'Manganese Oxides'-
'var: Manganese Dendrites'-
Opal
var: Common Opal
-SiO2 · nH2O

List of minerals for each chemical element

HHydrogen
H OpalSiO2 · nH2O
H CacoxeniteFe243+AlO6(PO4)17(OH)12 · 75H2O
H WavelliteAl3(PO4)2(OH,F)3 · 5H2O
H Opal (var: Common Opal)SiO2 · nH2O
H RockbridgeiteFe2+Fe43+(PO4)3(OH)5
H EleonoriteFe63+(PO4)4O(OH)4 · 6H2O
H StrengiteFePO4 · 2H2O
H MetavivianiteFe2+Fe23+(PO4)2(OH)2 · 6H2O
H VarisciteAlPO4 · 2H2O
OOxygen
O OpalSiO2 · nH2O
O CacoxeniteFe243+AlO6(PO4)17(OH)12 · 75H2O
O WavelliteAl3(PO4)2(OH,F)3 · 5H2O
O Opal (var: Common Opal)SiO2 · nH2O
O RockbridgeiteFe2+Fe43+(PO4)3(OH)5
O EleonoriteFe63+(PO4)4O(OH)4 · 6H2O
O StrengiteFePO4 · 2H2O
O MetavivianiteFe2+Fe23+(PO4)2(OH)2 · 6H2O
O VarisciteAlPO4 · 2H2O
FFluorine
F WavelliteAl3(PO4)2(OH,F)3 · 5H2O
AlAluminium
Al CacoxeniteFe243+AlO6(PO4)17(OH)12 · 75H2O
Al WavelliteAl3(PO4)2(OH,F)3 · 5H2O
Al VarisciteAlPO4 · 2H2O
SiSilicon
Si OpalSiO2 · nH2O
Si Opal (var: Common Opal)SiO2 · nH2O
PPhosphorus
P CacoxeniteFe243+AlO6(PO4)17(OH)12 · 75H2O
P WavelliteAl3(PO4)2(OH,F)3 · 5H2O
P RockbridgeiteFe2+Fe43+(PO4)3(OH)5
P EleonoriteFe63+(PO4)4O(OH)4 · 6H2O
P StrengiteFePO4 · 2H2O
P MetavivianiteFe2+Fe23+(PO4)2(OH)2 · 6H2O
P VarisciteAlPO4 · 2H2O
FeIron
Fe CacoxeniteFe243+AlO6(PO4)17(OH)12 · 75H2O
Fe RockbridgeiteFe2+Fe43+(PO4)3(OH)5
Fe EleonoriteFe63+(PO4)4O(OH)4 · 6H2O
Fe StrengiteFePO4 · 2H2O
Fe MetavivianiteFe2+Fe23+(PO4)2(OH)2 · 6H2O

Geochronology

Mineralization age: Mississippian : 341 Ma to 326.4 ± 1.6 Ma

Important note: This table is based only on rock and mineral ages recorded below and is not necessarily a complete representation of the geochronology, but does give an indication of possible mineralization events relevant to this locality. As more age information is added this table may expand in the future. A break in the table simply indicates a lack of data entered here, not necessarily a break in the geologic sequence. Grey background entries are from different, related, localities.

Geologic TimeRocks, Minerals and Events
Phanerozoic
 Paleozoic
  Carboniferous
   Mississippian
ⓘ Mudstone (youngest age)326.4 ± 1.6 Ma
ⓘ Siltstone (youngest age)326.4 ± 1.6 Ma
ⓘ Greywacke (youngest age)326.4 ± 1.6 Ma
ⓘ Mudstone (oldest age)341 Ma
ⓘ Siltstone (oldest age)341 Ma
ⓘ Greywacke (oldest age)341 Ma

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

Late Carboniferous
298.9 - 323.2 Ma



ID: 3157938
Clackmannan Group

Age: Pennsylvanian (298.9 - 323.2 Ma)

Stratigraphic Name: Clackmannan Group

Lithology: Major:{sandstone}, Minor{siltstone,mudstone}

Reference: Asch, K. The 1:5M International Geological Map of Europe and Adjacent Areas: Development and Implementation of a GIS-enabled Concept. Geologisches Jahrbuch, SA 3. [147]

Namurian - Famennian
315 - 372.2 Ma



ID: 2035892
Teign Valley Group

Age: Paleozoic (315 - 372.2 Ma)

Stratigraphic Name: Teign Valley Group

Lithology: Mudstone, siltstone and sandstone

Reference: British Geological Survey. DiGMapGB-625. British Geological Survey ©NERC. [23]

Early Carboniferous
323.2 - 358.9 Ma



ID: 3192903
Paleozoic sedimentary rocks

Age: Mississippian (323.2 - 358.9 Ma)

Lithology: Sedimentary rocks

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License


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