Greensand
Encyclopedia
Sand
Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...
or sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
, which has a greenish color. This term is specifically applied to shallow marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
, that contains noticeable quantities of rounded greenish grains. These grains are called glauconies and consist of a mixture of mixed-layer clay minerals,such as smectite and glauconite
Glauconite
Glauconite is an iron potassium phyllosilicate mineral of characteristic green color with very low weathering resistance and very friable.It crystallizes with a monoclinic geometry...
mica. Greensand is also loosely applied to any glauconitic sediment.
Formation
GreensandGreensand
Greensand or Green sand is either a sand or sandstone, which has a greenish color. This term is specifically applied to shallow marine sediment, that contains noticeable quantities of rounded greenish grains. These grains are called glauconies and consist of a mixture of mixed-layer clay...
forms in anoxic
Anoxic sea water
Anoxic waters are areas of sea water or fresh water that are depleted of dissolved oxygen. This condition is generally found in areas that have restricted water exchange....
marine
Marine
Marine may refer to:* Marine , a member of the military in an infantry or amphibious force under the authority of a navy, or in several cases, of an independent amphibious force...
environments that are rich in organic
Organic
Organic may refer to:* Of or relating to an organism, a living entity* Of or relating to an organ- Chemistry :* Organic matter, matter that has come from a once-living organism, is capable of decay or the product of decay, or is composed of organic compound* Organic chemistry, chemistry involving...
detritus and low in sedimentary input. Having accumulated in marine environments, greensands can be fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
-rich, such as in the late-Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
deposits of New Jersey, USA.
Occurrence
Important exposures are known from both northern and western EuropeEurope
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, and north Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
. Well known and important greensands are the Upper and Lower Greensands of England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
and occur within Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
and Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
sedimentary strata underlying the coastal plains of New Jersey
New Jersey
New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...
and Delaware
Delaware
Delaware is a U.S. state located on the Atlantic Coast in the Mid-Atlantic region of the United States. It is bordered to the south and west by Maryland, and to the north by Pennsylvania...
. Although greensand has been found throughout Phanerozoic
Phanerozoic
The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years and goes back to the time when diverse hard-shelled animals first appeared...
and Late Precambrian
Precambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
sedimentary deposits, it appears to to be most common in Eocene, Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
, and Cretaceous sedimentary deposits for unknown reasons.
Great Britain
In Great BritainGreat Britain
Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...
, greensand usually refers to specific rock strata of Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
age. A distinction is made between the Upper Greensand and Lower Greensand; the term greensand was originally applied by William Smith
William Smith (geologist)
William 'Strata' Smith was an English geologist, credited with creating the first nationwide geological map. He is known as the "Father of English Geology" for collating the geological history of England and Wales into a single record, although recognition was very slow in coming...
to glauconitic sandstones in the west of England and subsequently used for the similar deposits of the Weald
Weald
The Weald is the name given to an area in South East England situated between the parallel chalk escarpments of the North and the South Downs. It should be regarded as three separate parts: the sandstone "High Weald" in the centre; the clay "Low Weald" periphery; and the Greensand Ridge which...
, before it was appreciated that the latter are actually two distinct formations separated by the Gault Clay
Gault Clay
Gault is a clay formation of stiff blue clay deposited in a calm, fairly deep water marine environment during the Lower Cretaceous Period...
.
Both Upper and Lower Greensand outcrops appear in the scarp slopes surrounding the London Basin
London Basin
The London Basin is an elongated, roughly triangular sedimentary basin approximately long which underlies London and a large area of south east England, south eastern East Anglia and the adjacent North Sea...
and the Weald.
Prominent seams are to be found in the Vale of White Horse
Vale of White Horse
The Vale of White Horse is a local government district of Oxfordshire in England. The main town is Abingdon, other places include Faringdon and Wantage. There are 68 parishes within the district...
, in Bedfordshire
Bedfordshire
Bedfordshire is a ceremonial county of historic origin in England that forms part of the East of England region.It borders Cambridgeshire to the north-east, Northamptonshire to the north, Buckinghamshire to the west and Hertfordshire to the south-east....
, in Kent
Kent
Kent is a county in southeast England, and is one of the home counties. It borders East Sussex, Surrey and Greater London and has a defined boundary with Essex in the middle of the Thames Estuary. The ceremonial county boundaries of Kent include the shire county of Kent and the unitary borough of...
, Surrey
Surrey
Surrey is a county in the South East of England and is one of the Home Counties. The county borders Greater London, Kent, East Sussex, West Sussex, Hampshire and Berkshire. The historic county town is Guildford. Surrey County Council sits at Kingston upon Thames, although this has been part of...
, the South Downs National Park
South Downs National Park
The South Downs National Park is England's newest National Park, having become fully operational on 1 April 2011. The park, covering an area of in southern England, stretches for from Winchester in the west to Eastbourne in the east through the counties of Hampshire, West Sussex and East Sussex...
and Hampshire
Hampshire
Hampshire is a county on the southern coast of England in the United Kingdom. The county town of Hampshire is Winchester, a historic cathedral city that was once the capital of England. Hampshire is notable for housing the original birthplaces of the Royal Navy, British Army, and Royal Air Force...
and the Jurassic Coast
Jurassic Coast
The Jurassic Coast is a World Heritage Site on the English Channel coast of southern England. The site stretches from Orcombe Point near Exmouth in East Devon to Old Harry Rocks near Swanage in East Dorset, a distance of ....
in Dorset
Dorset
Dorset , is a county in South West England on the English Channel coast. The county town is Dorchester which is situated in the south. The Hampshire towns of Bournemouth and Christchurch joined the county with the reorganisation of local government in 1974...
.
The soil of the greensand is quite varied, ranging from fertile to fairly sterile. On the fertile soils chestnut
Chestnut
Chestnut , some species called chinkapin or chinquapin, is a genus of eight or nine species of deciduous trees and shrubs in the beech family Fagaceae, native to temperate regions of the Northern Hemisphere. The name also refers to the edible nuts they produce.-Species:The chestnut belongs to the...
and stands of hazel
Hazel
The hazels are a genus of deciduous trees and large shrubs native to the temperate northern hemisphere. The genus is usually placed in the birch family Betulaceae, though some botanists split the hazels into a separate family Corylaceae.They have simple, rounded leaves with double-serrate margins...
and oak
Oak
An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...
are common, while Scots Pine
Scots Pine
Pinus sylvestris, commonly known as the Scots Pine, is a species of pine native to Europe and Asia, ranging from Scotland, Ireland and Portugal in the west, east to eastern Siberia, south to the Caucasus Mountains, and as far north as well inside the Arctic Circle in Scandinavia...
and Birch
Birch
Birch is a tree or shrub of the genus Betula , in the family Betulaceae, closely related to the beech/oak family, Fagaceae. The Betula genus contains 30–60 known taxa...
colonise the poorer soils. These Greensand Ridge
Greensand Ridge
The Greensand Ridge is an extensive, prominent, often heavily wooded, sandstone escarpment and range of hills in south-east England. It runs in a horseshoe shape around the Weald of Surrey, Sussex and Kent. It reaches its highest elevation, , at Leith Hill in Surrey—the second highest point...
s are popular long distance walking routes, for instance the Greensand Way
Greensand Way
The Greensand Way is long distance walk of in southeast England, from Haslemere in Surrey to Hamstreet in Kent. It follows the Greensand Ridge along the Surrey Hills and Chart Hills. The route is mostly rural, passing through woods, and alongside fruit orchards and hop farms in Kent and links...
in Kent.
Lower Greensand
The Lower Greensand (known as the Woburn Sand north of the London Basin
London Basin
The London Basin is an elongated, roughly triangular sedimentary basin approximately long which underlies London and a large area of south east England, south eastern East Anglia and the adjacent North Sea...
) is of Aptian
Aptian
The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous epoch or series and encompasses the time from 125.0 ± 1.0 Ma to 112.0 ± 1.0 Ma , approximately...
age. In the Weald the Lower Greensand consists of four deposits which are partly diachronous
Diachronous
A diachronous deposit in Geology is a sedimentary rock formation in which apparently similar material varies in age from place to place....
: the Atherfield Clay 15 – thick, the Folkestone Beds 60 – thick; the Hythe beds 60 – thick and the Sandgate Beds 5 – thick. Although it appears both north and south of the London Basin it is not present everywhere beneath the Chalk which underlies the basin; the Gault lies directly on eroded Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
or Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
rocks under much of the area.
Upper Greensand
The Upper Greensand is of Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...
age. It represents a sandy lithofacies deposited in areas of stronger currents than the Gault Clay
Gault Clay
Gault is a clay formation of stiff blue clay deposited in a calm, fairly deep water marine environment during the Lower Cretaceous Period...
. Like the Lower Greensand it is not present beneath the whole of the London Basin, apparently passing laterally into Gault clay east of a line between Dunstable
Dunstable
Dunstable is a market town and civil parish located in Bedfordshire, England. It lies on the eastward tail spurs of the Chiltern Hills, 30 miles north of London. These geographical features form several steep chalk escarpments most noticeable when approaching Dunstable from the north.-Etymology:In...
and Tatsfield
Tatsfield
Tatsfield is a village of some 1800 inhabitants located in the Tandridge district of Surrey, England, and 16 miles south south-east of Charing Cross in London...
and of uncertain extent to the east of London.
Outcrops of the Upper Greensand occur in the south-west of England including the Blackdown Hills
Blackdown Hills
The Blackdown Hills are a range of hills along the Somerset-Devon border in south-western England, which were designated an Area of Outstanding Natural Beauty in 1991....
and East Devon Plateau and the Haldon Hills
Haldon
The Haldon Hills, usually known simply as Haldon, is a ridge of high ground in Devon, England. It is situated between the River Exe and the River Teign and runs northwards from Teignmouth, on the coast, for about until it dwindles away north west of Exeter at the River Yeo, just south of Crediton...
, remnants of a once much wider extent.
in well-water treatment systems it removes dissolved (reduced) iron
Properties and uses
The green colour of greensand is due to variable amounts of the mineralMineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
glauconite
Glauconite
Glauconite is an iron potassium phyllosilicate mineral of characteristic green color with very low weathering resistance and very friable.It crystallizes with a monoclinic geometry...
, an iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
silicate
Silicate
A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...
with very low weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
resistance; as a result, greensand tends to be weak and friable. It is a common ingredient as a source of potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
in organic
Organic
Organic may refer to:* Of or relating to an organism, a living entity* Of or relating to an organ- Chemistry :* Organic matter, matter that has come from a once-living organism, is capable of decay or the product of decay, or is composed of organic compound* Organic chemistry, chemistry involving...
gardening and farming
Organic farming
Organic farming is the form of agriculture that relies on techniques such as crop rotation, green manure, compost and biological pest control to maintain soil productivity and control pests on a farm...
fertilisers. Greensand glauconite is used as a water softener for its chemical-exchange properties. Greensand coated with manganese oxide (called manganese greensand) is used in well water treatment systems to remove dissolved (reduced) iron and manganese with the addition of an oxidant, usually potassium permanganate, under controlled pH conditions. It is also used as a type of rock for stone walls in areas where greensand is common.
In Roman times coarse grits derived from the lower greensand were used to line the inner surface of mortaria (grinding bowls) produced in the Oxfordshire pottery kilns.