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A mineral is a naturally occurring substance that is solid and stable at room temperature, representable by a chemical formula, usually abiogenic, and has an ordered atomic structure. It is different from a rock, which can be an aggregate of minerals or non-minerals, and does not have a specific chemical composition. The exact definition of a mineral is under debate, especially with respect to the requirement a valid species be abiogenic, and to a lesser extent with regards to it having an ordered atomic structure. The study of minerals is called mineralogy.

There are over 4,900 known mineral species; over 4,660 of these have been approved by the International Mineralogical Association (IMA). The silicate minerals compose over 90% of the Earth's crust. The diversity and abundance of mineral species is controlled by the Earth's chemistry. Silicon and oxygen constitute approximately 75% of the Earth's crust, which translates directly into the predominance of silicate minerals. Minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish various species, and these properties in turn are influenced by the mineral's geological environment of formation. Changes in the temperature, pressure, and bulk composition of a rock mass cause changes in its mineralogy; however, a rock can maintain its bulk composition, but as long as temperature and pressure change, its mineralogy can change as well.

Minerals can be described by variable physical properties which relate to its chemical structure and composition. Common distinguishing characteristics include crystal structure and habit, hardness, lustre, diaphaneity, colour, streak, tenacity, cleavage, fracture, parting, and specific gravity. More specific tests for minerals include reaction to acid, magnetism, taste or smell, and radioactivity.

Minerals are classified by key chemical constituents; the two dominant systems are the Dana classification and the Strunz classification. The silicate class of minerals is subdivided into six subclasses by the degree of polymerization in the chemical structure. All silicate minerals have a base unit of a [SiO4]4- silica tetrahedra—that is, a silicon cation coordinated by four oxygen anions, which gives the shape of a tetrahedron. These tetrahedra can be polymerized to give the subclasses: orthosilicates (no polymerization, thus single tetrahedra), disilicates (two tetrahedra bonded together), cyclosilicates (rings of tetrahedra), inosilicates (chains of tetrahedra), phyllosilicates (sheets of tetrahedra), and tectosilicates (three-dimensional network of tetrahedra). Other important mineral groups include the native elements, sulfides, oxides, halides, carbonates, sulfates, and phosphates.Exmoor is loosely defined as an area of hilly open moorland in west Somerset and north Devon in South West England, named after the River Exe the source of which is situated in the centre of the area, 2 miles NW of Simonsbath. Exmoor is more precisely defined as the area of the former synonymous ancient royal hunting forest, officially surveyed 1815–1818 as 18,810 acres in extent.[1] Even more precisely Exmoor is defined as the remnant of the royal forest of 18,810 acres allotted to the king in 1815, equating to 12/22nds of the total, in acres 10,262 1/4, which was sold to John Knight (1765–1850) in 1818, which comprises the present Exmoor Parish, whose parish church is situated in Simonsbath.[2] The moor has given its name to a National Park, which includes the Brendon Hills, the East Lyn Valley, the Vale of Porlock and 55 kilometres (34 mi) of the Bristol Channel coast. The total area of the Exmoor National Park is 692.8 square kilometres (267.5 sq mi), of which 71% is in Somerset and 29% in Devon.[3]

Contents [hide]

1 Exmoor National Park

2 Geology

2.1 Coastline

2.2 Rivers

3 Climate

4 History

4.1 Establishment of royal forest

4.2 Wardens

5 Wool trade

6 Ecology

6.1 Flora

6.2 Fauna

6.3 Beast

7 Government and politics

8 Sport and recreation

9 Places of interest

10 See also

11 References

12 Further reading

13 External links

[edit]Exmoor National Park

Exmoor was designated a National Park in 1954, under the 1949 National Parks and Access to the Countryside Act.[4] The Exmoor National Park is primarily an upland area with a dispersed population living mainly in small villages and hamlets. The largest settlements are Porlock, Dulverton, Lynton, and Lynmouth, which together contain almost 40% of the park's population. Lynton and Lynmouth are combined into one parish and are connected by the Lynton and Lynmouth Cliff Railway. Exmoor was once a Royal forest and hunting ground, which was sold off in 1818. Several areas within the Exmoor National Park have been declared Sites of Special Scientific Interest due to their flora and fauna. This title earns the site some legal protection from development, damage and neglect. In 1993 an Environmentally Sensitive Area was established within Exmoor.

Exmoor is an upland of sedimentary rocks classified as gritstones, sandstones, slate, shale and limestone, siltstones, and mudstones depending on the particle size. They are largely from the Devonian and early Carboniferous periods (the name Devonian comes from Devon, as rocks of that age were first studied and described here). As this area of Britain was not subject to glaciation, the plateau remains as a remarkably old landform.[5][6] Quartz and iron mineralisation can be detected in outcrops and subsoil.[7] The Glenthorne area demonstrates the Trentishoe Formation of the Hangman Sandstone Group. The Hangman Sandstone represents the Middle Devonian sequence of North Devon and Somerset.[8] These unusual freshwater deposits in the Hangman Grits, were mainly formed in desert conditions.[9] The underlying rocks are covered by moors and supported by wet, acid soil.[10] The highest point on Exmoor is Dunkery Beacon; at 519 metres (1,703 ft) it is also the highest point in Somerset.[11]