Carbonate minerals are those minerals containing the carbonate ion, CO32−. Calcite group: trigonal Calcite CaCO3 Gaspeite CO3 Magnesite MgCO3 Otavite CdCO3 Rhodochrosite MnCO3 Siderite FeCO3 Smithsonite ZnCO3 Spherocobaltite CoCO3 Aragonite group: orthorhombic Aragonite CaCO3 Cerussite PbCO3 Strontianite SrCO3 Witherite BaCO3 Rutherfordine UO2CO3 Natrite Na2CO3 Dolomite group: trigonal Ankerite CaFe2 Dolomite CaMg2 Huntite Mg3Ca4 Minrecordite CaZn2 Barytocite BaCa2 Carbonate with hydroxide: monoclinic Azurite Cu322 Hydrocerussite Pb322 Malachite Cu2CO32 Rosasite 2CO32 Phosgenite Pb2Cl2 Hydrozincite Zn526 Aurichalcite 526 Hydromagnesite Mg542.4H2O Ikaite CaCO3·6 Lansfordite MgCO3·5 Monohydrocalcite CaCO3·H2O Natron Na2CO3·10 Zellerite Ca2·5The carbonate class in both the Dana and the Strunz classification systems include the nitrates. IMA-CNMNC proposes a new hierarchical scheme; this list uses the classification of Nickel–Strunz. Abbreviations: "*" – discredited. "?" – questionable/doubtful.
"REE" – Rare-earth element "PGE" – Platinum-group element 03. C Aluminofluorides, 06 Borates, 08 Vanadates, 09 Silicates: Neso: insular Soro: grouping Cyclo: ring Ino: chain Phyllo: sheet Tekto: three-dimensional framework Nickel–Strunz code scheme: NN. XY.##x NN: Nickel–Strunz mineral class number X: Nickel–Strunz mineral division letter Y: Nickel–Strunz mineral family letter ##x: Nickel–Strunz mineral/group number, x add-on letter 05. A Carbonates without additional anions, without H2O 05. AA Alkali carbonates: 05 Zabuyelite. AB Alkali-earth carbonates: 05 Calcite, 05 Gaspeite, 05 Magnesite, 05 Rhodochrosite, 05 Otavite, 05 Spherocobaltite, 05 Siderite, 05 Smithsonite. AC Alkali and alkali-earth carbonates: 05 Eitelite, 10 Nyerereite, 10 Natrofairchildite, 10 Zemkorite. AD With rare-earth elements: 05 Sahamalite-. B Carbonates with additional anions, without H2O 05. BA With Cu, Co, Ni, Zn, Mg, Mn: 05 Azurite, 10 Chukanovite, 10 Malachite, 10 Georgeite, 10 Pokrovskite, 10 Nullaginite, 10 Glaukosphaerite, 10 Mcguinnessite, 10 Kolwezite, 10 Rosasite, 10 Zincrosasite.
BB With alkalies, etc.: 05 Barentsite, 10 Dawsonite, 15 Tunisite, 20 Sabinaite 05. BC With alkali-earth cations: 05 Brenkite, 10 Rouvilleite, 15 Podlesnoite 05. BD With rare-earth elements: 05 Cordylite-, 05 Lukechangite-. BE With Pb, Bi: 05 Shannonite, 10 Hydrocerussite, 15 Plumbonacrite, 20 Phosgenite, 25 Bismutite, 30 Kettnerite, 35 Beyerite 05. BF With, SO4, PO4, TeO3: 05 Northupite, 05 Ferrotychite, 05 Manganotychite, 05 Tychite. C Carbonates without additional anions, with H2O 05. CA With medium-sized cations: 05 Nesquehonite, 10 Lansfordite, 15 Barringtonite, 20 Hellyerite 05. CB With large cations: 05 Thermonatrite, 10 Natron, 15 Trona, 20 Monohydrocalcite, 25 Ikaite, 30 Pirssonite, 35 Gaylussite, 40 Chalconatronite, 45 Baylissite, 50 Tuliokite 05. CC With rare-earth elements: 05 Donnayite-, 05 Mckelveyite-*, 05 Mckelveyite-, 05 Weloganite. D Carbonates with additional anions, with H2O 05. DA With medium-sized cations: 05 Dypingite, 05 Giorgiosite, 05 Hydromagnesite, 05 Widgiemoolthalite.
DB With large and medium-sized cations: 05 Alumohydrocalcite, 05 Para-alumohydrocalcite, 05 Nasledovite.
Old Red Sandstone
The Old Red Sandstone is an assemblage of rocks in the North Atlantic region of Devonian age. It extends in the east across Great Britain and Norway, in the west along the northeastern seaboard of North America, it extends northwards into Greenland and Svalbard. In Britain it is a lithostratigraphic unit to which stratigraphers accord supergroup status and, of considerable importance to early paleontology. For convenience the short version of the term, ORS is used in literature on the subject; the term was coined to distinguish the sequence from the younger New Red Sandstone which occurs throughout Britain. The Old Red Sandstone describes a suite of sedimentary rocks deposited in a variety of environments during the Devonian but extending back into the late Silurian and on into the earliest part of the Carboniferous; the body of rock, or facies, is dominated by alluvial sediments and conglomerates at its base, progresses to a combination of dunes and river sediments. The familiar red colour of these rocks arises from the presence of iron oxide but not all the Old Red Sandstone is red or sandstone — the sequence includes conglomerates, mudstones and thin limestones and colours can range from grey and green through to red and purple.
These deposits are associated with the erosion of the Caledonian Mountain chain, thrown up by the collision of the former continents of Avalonia and Laurentia to form the Old Red Sandstone Continent- an event known as the Caledonian Orogeny. Many fossils are found within the rocks, including early fishes and plants; the rocks may appear paleontologically barren to amateur geologists but careful study with an accomplished fossil hunter, can uncover pockets of fossils. Rocks of this age were laid down in southwest England though these are of true marine origin and are not included within the Old Red Sandstone. Since the Old Red Sandstone consists predominantly of rocks of terrestrial origin, it does not contain marine fossils which would otherwise prove useful in correlating one occurrence of the rock with another, both between and within individual sedimentary basins. Accordingly, local stage names were devised and these remain in use to some extent today though there is an increasing use of international stage names.
Thus in the Anglo-Welsh Basin, there are frequent references to the Downtonian, Dittonian and Farlovian stages in the literature. The existence of a number of distinct sedimentary basins throughout Britain has been established; the Orcadian Basin extends over a wide area of the neighbouring seas. It encompasses the Moray Firth and adjoining land areas, Caithness and parts of Shetland. South of the Moray Firth, two distinct sub-basins are recognised at Rhynie; the sequence is more than 4 kilometres thick in parts of Shetland. The main basin is considered to be an intramontane basin resulting from crustal rifting associated with post-Caledonian extension accompanied by strike-slip faulting along the Great Glen Fault system. There are a scatter of exposures of the Old Red Sandstone around the Oban area on the West Highland coast where a conglomerate of andesite boulders rests unconformably on Dalradian schists of the Easdale Subgroup, they are interpreted as alluvial fans which filled a depositional basin from the northeast.
The deposits are obvious on Kerrera where they form the bedrock across half of the island. The Kerrera Sandstone Formation is up to 128m thick in its type area and consists of green and red sandstones and conglomerates accompanied by siltstones and limestones. Small outliers occur near either side of Loch Avich; the Midland Valley graben defined by the Highland Boundary Fault in the north and the Southern Uplands Fault in the south harbours not only a considerable amount of Old Red Sandstone sedimentary rocks but igneous rocks of this age associated with extensive volcanism. There is a continuous outcrop along the Highland Boundary Fault from Stonehaven on the North Sea coast to Helensburgh and beyond to Arran. A more disconnected series of outcrops occur along the line of the Southern Uplands Fault from Edinburgh to Girvan. Old Red Sandstone occurs in conjunction with conglomerate formations, one such noteworthy cliffside exposure being the Fowlsheugh Nature Reserve, Kincardineshire. A series of outcrops occur from East Lothian southwards through Berwickshire.
Hutton's famous unconformity at Siccar Point occurs within this basin - see History of study below. This large basin extends across much of South Wales from southern Pembrokeshire in the west through Carmarthenshire into Powys and Monmouthshire and through the southern Welsh Marches, notably into Herefordshire and Gloucestershire. Outliers in Somerset and north Devon complete the extent of this basin. With the exception of south Pembrokeshire, all parts of the basin are represented by a range of lithologies assigned to the Lower Devonian and to the Upper Devonian, the contact between the two being unconformable and representing the complete omission of any Middle Devonian sequence; the lowermost formations are of upper Silurian age, these being the Downton Castle Sandstone Formation and the overlying Raglan Mudstone Formation except in Pembrokeshire where a more complex series of formations is recognised. In the east of the basin, the top of the Raglan Mudstone is marked by a well-developed calcrete, the Bishop's Frome Limestone.
The lowermost Devonian formation is the St Maughans Formation, itself overlain by the Brownstones Formation though with an intervening Senni Formation over much of the area
Red Beds of Texas and Oklahoma
The Red Beds of Texas and Oklahoma are a group of Early Permian-age geologic strata in the southwestern United States outcropping in north-central Texas and south-central Oklahoma. They comprise several stratigraphic groups including the Clear Fork Group, the Wichita Group, the Pease River Group; the Red Beds were first explored by American paleontologist Edward Drinker Cope starting in 1877. Fossil remains of many Permian tetrapods have been found in the Red Beds, including those of Dimetrodon, Seymouria and Eryops. A recurring feature in many of these animals is the sail structure on their back. Deposits dating from the Permian are present contiguously stretching from central Texas all the way into southern Nebraska. In Nebraska and Kansas, deposits of light-colored limestone are frequent, while red-colored rocks are rare. In Oklahoma, the light-colored limestone transitions into red-colored sandstone and shale until the limestone is nonexistent in north-central Texas; the portion of the red beds with abundant fossil deposits is in Texas between the Red River and the Salt Fork Brazos River.
The area includes the city of Wichita Falls, as well as rural communities such as Seymour and Archer City. The Texas and Oklahoma red beds are sedimentary rocks consisting of sandstone and red mudstone; the red color of the rocks is due to the presence of ferric oxide. The rocks were deposited during the early Permian in a warm, moist climate, with seasonal periods of dry conditions; the Texas and Oklahoma red beds can be split into three primary stratigraphic groups: the Wichita Group, the Clear Fork Group, the Pease River Group. The Wichita Group is the oldest of the three groups; the Wichita Group contains some of the richest fossil deposits in the red beds, including the Geraldine Bonebed in Archer County. The Pease River Group is the most recent deposition, occurring during the Guadalupian epoch; the Clear Fork Group is in between the other two, being deposited during the Kungurian age. The stratigraphic groups are layered such that the Pease River Group overlies the Clear Fork Group, which overlies the Wichita group.
In 1877, Edward Drinker Cope was the first paleontologist to study the red beds in search of fossils. Cope employed collectors to aid him in his search for bones, including the Swiss botanist Jacob Boll. After Boll's death in 1880 while collecting, Cope employed a preacher named W. F. Cummins to continue the search. After Cope, paleontologists such as Ermine Cowles Case and Alfred Romer found rich deposits of Permian-era tetrapods; the most prolific fossil site in the red beds is the Geraldine Bonebed within the Wichita Group. During the Permian, the bonebed was the site of a freshwater pond, which after a catastrophic event became the burial site for a variety of terrestrial and marine animals; as a result, the bonebed contains a cross-section of life during the early Permian. Plant remains found in the bonebed include Calamites and conifers. Marine life present in the bonebed include Xenacanthus and lungfish; the Geraldine Bonebed is most famous as a prolific source of temnospondyls, basal reptiliomorphs and reptiles, including partial and complete skeletons of Archeria, Edaphosaurus, Bolosaurus, Trimerorhachis and Ophiacodon.
The Clear Fork Group contains multiple fossil sites. Like the Geraldine Bonebed and other Wichita Group sites, The Clear Fork Group is most famous for its early Permian amphibian deposits Seymouria baylorensis; the species and genus were first discovered in 1904 by the German paleontologist Ferdinand Broili. Seymouria baylorensis is named for the location of its discovery in Baylor County near the city of Seymour; as one of the few Seymouria bone sites in the world, paleontologists have studied the Clear Fork deposit for evidence of Seymouria as a transitional fossil between aquatic and terrestrial animals, as well as Seymouria's close relationship to amniotes. The Clear Fork Group contains deposits of plant species throughout different sections of the Clear Fork Group; the increasing prevalence of seed plants with pockets of water-based plants can be used to infer a wet, but drying climate. Geology of Wichita Falls, Texas Geology of Texas Paleontology in Texas
The Carboniferous is a geologic period and system that spans 60 million years from the end of the Devonian Period 358.9 million years ago, to the beginning of the Permian Period, 298.9 Mya. The name Carboniferous means "coal-bearing" and derives from the Latin words carbō and ferō, was coined by geologists William Conybeare and William Phillips in 1822. Based on a study of the British rock succession, it was the first of the modern'system' names to be employed, reflects the fact that many coal beds were formed globally during that time; the Carboniferous is treated in North America as two geological periods, the earlier Mississippian and the Pennsylvanian. Terrestrial animal life was well established by the Carboniferous period. Amphibians were the dominant land vertebrates, of which one branch would evolve into amniotes, the first terrestrial vertebrates. Arthropods were very common, many were much larger than those of today. Vast swaths of forest covered the land, which would be laid down and become the coal beds characteristic of the Carboniferous stratigraphy evident today.
The atmospheric content of oxygen reached its highest levels in geological history during the period, 35% compared with 21% today, allowing terrestrial invertebrates to evolve to great size. The half of the period experienced glaciations, low sea level, mountain building as the continents collided to form Pangaea. A minor marine and terrestrial extinction event, the Carboniferous rainforest collapse, occurred at the end of the period, caused by climate change. In the United States the Carboniferous is broken into Mississippian and Pennsylvanian subperiods; the Mississippian is about twice as long as the Pennsylvanian, but due to the large thickness of coal-bearing deposits with Pennsylvanian ages in Europe and North America, the two subperiods were long thought to have been more or less equal in duration. In Europe the Lower Carboniferous sub-system is known as the Dinantian, comprising the Tournaisian and Visean Series, dated at 362.5-332.9 Ma, the Upper Carboniferous sub-system is known as the Silesian, comprising the Namurian and Stephanian Series, dated at 332.9-298.9 Ma.
The Silesian is contemporaneous with the late Mississippian Serpukhovian plus the Pennsylvanian. In Britain the Dinantian is traditionally known as the Carboniferous Limestone, the Namurian as the Millstone Grit, the Westphalian as the Coal Measures and Pennant Sandstone; the International Commission on Stratigraphy faunal stages from youngest to oldest, together with some of their regional subdivisions, are: A global drop in sea level at the end of the Devonian reversed early in the Carboniferous. There was a drop in south polar temperatures; these conditions had little effect in the deep tropics, where lush swamps to become coal, flourished to within 30 degrees of the northernmost glaciers. Mid-Carboniferous, a drop in sea level precipitated a major marine extinction, one that hit crinoids and ammonites hard; this sea level drop and the associated unconformity in North America separate the Mississippian subperiod from the Pennsylvanian subperiod. This happened about 323 million years ago, at the onset of the Permo-Carboniferous Glaciation.
The Carboniferous was a time of active mountain-building as the supercontinent Pangaea came together. The southern continents remained tied together in the supercontinent Gondwana, which collided with North America–Europe along the present line of eastern North America; this continental collision resulted in the Hercynian orogeny in Europe, the Alleghenian orogeny in North America. In the same time frame, much of present eastern Eurasian plate welded itself to Europe along the line of the Ural Mountains. Most of the Mesozoic supercontinent of Pangea was now assembled, although North China, South China continents were still separated from Laurasia; the Late Carboniferous Pangaea was shaped like an "O." There were two major oceans in the Carboniferous—Panthalassa and Paleo-Tethys, inside the "O" in the Carboniferous Pangaea. Other minor oceans were shrinking and closed - Rheic Ocean, the small, shallow Ural Ocean and Proto-Tethys Ocean. Average global temperatures in the Early Carboniferous Period were high: 20 °C.
However, cooling during the Middle Carboniferous reduced average global temperatures to about 12 °C. Lack of growth rings of fossilized trees suggest a lack of seasons of a tropical climate. Glaciations in Gondwana, triggered by Gondwana's southward movement, continued into the Permian and because of the lack of clear markers and breaks, the deposits of this glacial period are referred to as Permo-Carboniferous in age; the cooling and drying of the climate led to the Carboniferous Rainforest Collapse during the late Carboniferous. Tropical rainforests fragmented and were devastated by climate change. Carboniferous rocks in Europe and eastern North America consist of a repeated sequence of limestone, sandstone and coal beds. In North America, the early Carboniferous is marine
Limonite is an iron ore consisting of a mixture of hydrated iron oxide-hydroxides in varying composition. The generic formula is written as FeO·nH2O, although this is not accurate as the ratio of oxide to hydroxide can vary quite widely. Limonite is one of the three principal iron ores, the others being hematite and magnetite, has been mined for the production of iron since at least 2500 BCE. Limonite is named for the Greek word λειμών, meaning "wet meadow", or λίμνη, meaning “marshy lake” as an allusion to its occurrence as bog iron ore in meadows and marshes. In its brown form it is sometimes called brown iron ore. In its bright yellow form it is sometimes called yellow iron ore. Limonite is dense with a specific gravity varying from 2.7 to 4.3. It varies in colour from a bright lemony yellow to a drab greyish brown; the streak of limonite on an unglazed porcelain plate is always brownish, a character which distinguishes it from hematite with a red streak, or from magnetite with a black streak.
The hardness is variable, but in the 4 - 5.5 range. Although defined as a single mineral, limonite is now recognized as a mixture of related hydrated iron oxide minerals, among them goethite, akaganeite and jarosite. Individual minerals in limonite may form crystals, but limonite does not, although specimens may show a fibrous or microcrystalline structure, limonite occurs in concretionary forms or in compact and earthy masses; because of its amorphous nature, occurrence in hydrated areas limonite presents as a clay or mudstone. However, there are limonite pseudomorphs after other minerals such as pyrite; this means that chemical weathering transforms the crystals of pyrite into limonite by hydrating the molecules, but the external shape of the pyrite crystal remains. Limonite pseudomorphs have been formed from other iron oxides and magnetite. Limonite forms from the hydration of hematite and magnetite, from the oxidation and hydration of iron rich sulfide minerals, chemical weathering of other iron rich minerals such as olivine, pyroxene and biotite.
It is the major iron component in lateritic soils. It is deposited in run-off streams from mining operations. One of the first uses was as a pigment; the yellow form produced yellow ochre for which Cyprus was famous, while the darker forms produced more earthy tones. Roasting the limonite changed it to hematite, producing red ochres, burnt umbers and siennas. Bog iron ore and limonite mudstones are mined as a source of iron, although commercial mining of them has ceased in the United States. Iron caps or gossans of siliceous iron oxide form as the result of intensive oxidation of sulfide ore deposits; these gossans were used by prospectors as guides to buried ore. In addition the oxidation of those sulfide deposits which contained gold resulted in the concentration of gold in the iron oxide and quartz of the gossans. Goldbearing limonite gossans were productively mined in the Shasta County, California mining district. Similar deposits were mined near Rio Tinto in Mount Morgan in Australia. In the Dahlonega gold belt in Lumpkin County, Georgia gold was mined from limonite-rich lateritic or saprolite soil.
The gold of the primary veins was concentrated into the limonites of the weathered rocks. In another example the weathered iron formations of Brazil served to concentrate gold with the limonite of the resulting soils. While the first iron ore was meteoric iron, hematite was far easier to smelt, in Africa, where the first evidence of iron metallurgy occurs, limonite is the most prevalent iron ore. Before smelting, as the ore was heated and the water driven off and more of the limonite was converted to hematite; the ore was pounded as it was heated above 1250 °C, at which temperature the metallic iron begins sticking together and non-metallic impurities are thrown off as sparks. Complex systems developed, notably in Tanzania, to process limonite. Nonetheless and magnetite remained the ores of choice when smelting was by bloomeries, it was only with the development of blast furnaces in 1st century BCE in China and about 1150 CE in Europe, that the brown iron ore of limonite could be used to best advantage.
As regards to the use of limonite for pigments, it was one of the earliest man-used materials and can be seen in Neolithic cave paintings and pictographs. Bog iron Iron ore Ore genesis Mineral galleries Mindat Gold and limonite
A floodplain or flood plain is an area of land adjacent to a stream or river which stretches from the banks of its channel to the base of the enclosing valley walls, which experiences flooding during periods of high discharge. The soils consist of levees and sands deposited during floods. Levees are the heaviest materials and they are deposited first. Floodplains are formed; when a river breaks its banks, it leaves behind layers of alluvium. These build up to create the floor of the plain. Floodplains contain unconsolidated sediments extending below the bed of the stream; these are accumulations of sand, loam, and/or clay, are important aquifers, the water drawn from them being pre-filtered compared to the water in the river. Geologically ancient floodplains are represented in the landscape by fluvial terraces; these are old floodplains that remain high above the present floodplain and indicate former courses of a stream. Sections of the Missouri River floodplain taken by the United States Geological Survey show a great variety of material of varying coarseness, the stream bed having been scoured at one place and filled at another by currents and floods of varying swiftness, so that sometimes the deposits are of coarse gravel, sometimes of fine sand or of fine silt.
It is probable that any section of such an alluvial plain would show deposits of a similar character. The floodplain during its formation is marked by meandering or anastomotic streams, oxbow lakes and bayous, marshes or stagnant pools, is completely covered with water; when the drainage system has ceased to act or is diverted for any reason, the floodplain may become a level area of great fertility, similar in appearance to the floor of an old lake. The floodplain differs, because it is not altogether flat, it has a gentle slope downstream, for a distance, from the side towards the center. The floodplain is the natural place for a river to dissipate its energy. Meanders form over the floodplain to slow down the flow of water and when the channel is at capacity the water spills over the floodplain where it is temporarily stored. In terms of flood management the upper part of the floodplain is crucial as this is where the flood water control starts. Artificial canalisation of the river here will have a major impact on wider flooding.
This is the basis of sustainable flood management. Floodplains can support rich ecosystems, both in quantity and diversity. Tugay forests form an ecosystem associated with floodplains in Central Asia, they are a category of riparian systems. A floodplain can contain 100 or 1,000 times as many species as a river. Wetting of the floodplain soil releases an immediate surge of nutrients: those left over from the last flood, those that result from the rapid decomposition of organic matter that has accumulated since then. Microscopic organisms thrive and larger species enter a rapid breeding cycle. Opportunistic feeders move in to take advantage; the production of nutrients falls away quickly. This makes floodplains valuable for agriculture. River flow rates are undergoing change following suit with climate change; this change is a threat to other floodplain forests. These forests have over time synced their seedling deposits after the spring peaks in flow to best take advantage of the nutrient rich soil generated by peak flow.
Many towns have been built on floodplains, where they are susceptible to flooding, for a number of reasons: access to fresh water. The worst of these, the worst natural disaster were the 1931 China floods, estimated to have killed millions; this had been preceded by the 1887 Yellow River flood, which killed around one million people, is the second-worst natural disaster in history. The extent of floodplain inundation depends in part on the flood magnitude, defined by the return period. In the United States the Federal Emergency Management Agency manages the National Flood Insurance Program; the NFIP offers insurance to properties located within a flood prone area, as defined by the Flood Insurance Rate Map, which depicts various flood risks for a community. The FIRM focuses on delineation of the 100-year flood inundation area known within the NFIP as the Special Flood Hazard Area. Where a detailed study of a waterway has been done, the 100-year floodplain will include the floodway, the critical portion of the floodplain which includes the stream channel and any adjacent areas that must be kept free of encroachments that might block flood flows or restrict storage of flood waters.
Another encountered term is the Special Flood Hazard Area, any area subject to inundation by the 100-year flood. A problem is that any alteration of the watershed upstream of the point in question can affect the ability of the watershed to handle water, thus affects the levels of the periodic floods. A large shopping center and parking lot, for example, may raise the levels of the 5-year, 100-year, other floods, but the maps are adjusted, are rendered
Siderite is the name of a type of iron meteorite. Siderite is a mineral composed of iron carbonate, it takes its name from the Greek word σίδηρος sideros, “iron”. It is a valuable iron mineral, since it contains no sulfur or phosphorus. Zinc and manganese substitute for the iron resulting in the siderite-smithsonite, siderite-magnesite and siderite-rhodochrosite solid solution series. Siderite has Mohs hardness of 3.75-4.25, a specific gravity of 3.96, a white streak and a vitreous lustre or pearly luster. It crystallizes in the trigonal crystal system, are rhombohedral in shape with curved and striated faces, it occurs in masses. Color ranges from black, the latter being due to the presence of manganese. Siderite is found in hydrothermal veins, is associated with barite, fluorite and others, it is a common diagenetic mineral in shales and sandstones, where it sometimes forms concretions, which can encase three-dimensionally preserved fossils. In sedimentary rocks, siderite forms at shallow burial depths and its elemental composition is related to the depositional environment of the enclosing sediments.
In addition, a number of recent studies have used the oxygen isotopic composition of sphaerosiderite as a proxy for the isotopic composition of meteoric water shortly after deposition. Although spathic iron ores, such as siderite, have been economically important for steel production, they are far from ideal as an ore, their hydrothermal mineralisation tends to form them as small ore lenses following steeply dipping bedding planes. This makes them not amenable to opencast working, increases the cost of working them by mining with horizontal stopes; as the individual ore bodies are small, it may be necessary to duplicate or relocate the pit head machinery, winding engine and pumping engine, between these bodies as each is worked out. This makes mining the ore an expensive proposition compared to typical ironstone or haematite opencasts; the recovered ore has drawbacks. The carbonate ore is more difficult to smelt than other oxide ore. Driving off the carbonate as carbon dioxide requires more energy and so the ore'kills' the blast furnace if added directly.
Instead the ore must be given a preliminary roasting step. Developments of specific techniques to deal with these ores began in the early 19th century with the work of Sir Thomas Lethbridge in Somerset. His'Iron Mill' of 1838 used a three-chambered concentric roasting furnace, before passing the ore to a separate reducing furnace for smelting. Details of this Mill were the invention of Charles Sanderson, a steel maker of Sheffield, who held the patent for it; these differences between spathic ore and haematite have led to the failure of a number of mining concerns, notably the Brendon Hills Iron Ore Company. Spathic iron ores have negligible phosphorus; this led to their one major benefit. Although the first demonstrations by Bessemer in 1856 had been successful attempts to reproduce this were infamously failures. Work by the metallurgist Robert Forester Mushet discovered that the reason for this was the nature of the Swedish ores that Bessemer had innocently used, being low in phosphorus. Using a typical European high-phosphorus ore in Bessemer's converter gave a poor quality steel.
To produce high quality steel from a high-phosphorus ore, Mushet realised that he could operate the Bessemer converter for longer, burning off all the steel's impurities including the unwanted phosphorus and the essential carbon, but re-adding carbon, with manganese, in the form of a obscure ferromanganese ore with no phosphorus, spiegeleisen. This created a sudden demand for spiegeleisen. Although it was not available in sufficient quantity as a mineral, steelworks such as that at Ebbw Vale in South Wales soon learned to make it from the spathic siderite ores. For a few decades, spathic ores were now in demand and this encouraged their mining. In time though, the original'acidic' liner, made from siliceous sandstone or ganister, of the Bessemer converter was replaced by a'basic' liner in the developed Gilchrist Thomas process; this removed the phosphorus impurities as slag, produced by chemical reaction with the liner, no longer required spiegeleisen. From the 1880s demand for the ores fell once again and many of their mines, including those of the Brendon Hills, closed soon after