Jet is a Fossilised Coal
Jet is a fossilised coal, from the ancient family of coniferous trees (Araucariaceae, commonly referred to as araucarians) and has no cleat and can be found on the sea shore near Whitby. It is particularly hard but can be fashioned into ornaments or jewellery.
Over the millions of years the movements of the earth, the enormous pressures, the sliding of the platelets etc, the strata, including the coal seams were uplifted on numerous occasions creating the Pennines and faulting, steep dips etc formed and distortion and erosion of the strata leading to the ‘coal measures’ being exposed at the surface in Derbyshire. Similarly at the edge of Charnwood Forest in the Leicestershire Coalfield ancient
Carboniferous rocks are exposed at the surface and the coal seams eroded by the uplift of the Ashby anticline. The Thrislington fault in the East cuts off the measures and some seams incrop.
It will be seen that many have been eroded away as in Derbyshire. Much of the area is overlain by new Red sandstone measures and in the South Derbyshire parts of the field beyond the Ashby anticline and the main Boothorpe fault and two other lesser known faults again the seams incrop below the overlying Red sandstone.
Some coal seams are thick, and obviously the conditions would have been just right, with continuous jungle type conditions, whilst other seams are thin, denoting leaner times. Sometimes the neighbouring seams combine to form a thicker or more workable seam. Some lie at a great depth and others at a shallow depth. Some coal seams are very gassy, whilst others are not. Seams have varying amounts of sulphur and chlorine and the ones with low proportions of each are more favoured. The deeper seams tend to have higher chlorine content. Some have dirt bands within the seam and others are clean. Certain coal seams are excellent for household use whilst others are only useful when blended with a better quality seam. Several coal seams have good coking properties but Cannel coal is no use for coking and needs to be sorted out at the surface. Some seams have several useful properties, e.g. Top Hard of which some bands in the seam are good for steam, other parts for household use, industrial use, gas and for coking. The Silkstone seam or Blackshale is generally a good coking coal and was much sought after for the iron and steel making industry.
Some of the seams are overlain with mudstone (bind or relative soft smooth shale), or siltstone (a coarser rock) or sandstone (a very coarse rock) and the relative ease of working of the roadways to the coalface depends upon the type. Some seams are more easily worked than others. Sometimes a band of coal has to be left to form a good roof as trying to extract all of the coal seam sometimes creates poor and dangerous conditions, generally with the strata above the seam continually falling down. Many seams have not even been attempted to be worked, being far too thin or poor quality. Some seams are very dusty when worked and some have a soft seat-earth floor or clunch whilst others have a bell metal or hard floor. Rarely coal had to be left in the floor to give a good working surface. At some pits fireclay and bind were worked in conjunction with the coal in order to manufacture bricks and pottery etc and sanitary ware, whilst at a few pits, ganister was worked with the coal.
The one thing that they all have in common is that the line of cleavage for the Coalfields lies in the same direction, approximately ESE / WNW. Could this be due to some kind of force like magnetism or such at the time the Earth was changing? Cleavage or cleat is the main fracture line in the coal seam where the coal breaks naturally or more easily. Sometimes in these breaks a very thin skim of calcite can be found. A minor cleat at right angles to the main cleat allowed large lumps to be mined. Sometimes calcite is also found in the hade of faults. The cleat was very important in the mining of the coal with hand got methods and the earlier cutting machines in particular and generally determined the layout or infrastructure of the pit.
The higher the hardness in coal and the vitreous black lustre generally points to the coal having a high rank, 69 – 86 lighter whereas the lower rank coals are typically softer and friable, with a higher moisture content and a duller appearance, and a lower carbon content, obviously not having such a high level of energy less than 69 (an immature coal). Within certain areas the conditions must have been absolutely right with further extreme pressures etc that caused the coals to become fully mature, to metamorphose into anthracite, the hardest of coals known, sometimes called stone coal and is in the top rank of coal, with high carbon, low moisture and having very high energy content. Maybe the term ‘black diamond’ for the coal, came from the fact that diamonds are a form of carbon that has been pressurised beyond anything known.......... However diamonds won’t burn, but coal will!
Anthracite is not found in the East Midlands. It has the highest coal rank 86 – 98 (rank 800, defined in the UK as more than 9% volatile content) and results from significant heating or pressure during burial. It is a metamorphic rock with more carbon than bituminous coal. Many UK anthracites are bright, very brittle, having very many cleat fractures, but at times difficult to mine. It breaks with conchoidal fractures but does not break easily, nor is it dusty and is clean to the touch and does not soil the fingers. Anthracites are found mainly in South Wales and in parts of Central Scotland. However it is found in other parts of the World. Apart from electricity generation (e.g. South Wales) it is used as a smokeless fuel, or in specialist carbon filter products.
Brown Coal or Lignite is an immature coal, a stage on from peat, and found in Ireland and Germany.
Iron Pyrites - The brasses or lumps of iron pyrites found in some seams were mined and sold to the makers of copperas, green vitriol or sulphate of iron.
These brasses (brass knockers) or iron pyrites (fool's gold) either in nodules or lenses as shown, would later in the 20th Century have to be sorted from the coal and discarded, particularly for power station use, where damage to the rollers that crush the coal can occur.
High chlorine content in the coal (when mixed with water creates hydrochloric acid) can cause damage to the power station grates and high sulphur content fills the air with pollution which when mixed with the atmosphere (sulphuric acid) can cause acid rain which can destroy plant and tree life.
Areas where brasses were noted are mainly: Alton; Ashover; Barlow; Staveley; Belper; Thatch-marsh; Buxton; Dore; Dronfield; Heanor; Shipley; Heanor; Swanwick; Alfreton etc.
Particularly in Derbyshire some bands or balls (nodules) of ironstone overlie the coal seams and were worked in conjunction with one another in the late 1700s and onwards. John Farey in the early 1800s lists the areas where ironstone was worked:-
Alfreton; Ashby Wolds; Ashgate in Chesterfield; Bagthorpe, Nottinghamshire; Berley Moor, Eckington; Birchett, Dronfield; Bramley, Eckington; Brampton, Chesterfield; Brimington, Chesterfield; Butterley, Pentrich; Calow, Chesterfield; Clay Cross, North Winfield (Wingfield); Codnor Park, Heanor; Cole Aston, Dronfield; Dale Abbey; Eckington area; Grass-moor, Chesterfield; Green-hill Lane, Alfreton; Hady, Chesterfield; Hasland, Chesterfield; Heage, Duffield; Henmore, North Wingfield; Higham, Shirland; High-lane, Eckington; Hill-top, Dronfield; Hollingwood-common, Staveley; Holmsfield, Dronfield; Ilkeston area; Inkersall, Staveley; Killamarsh, Eckington; Long-Duckmanton; Masborough; Morley-Park, Duffield; Mossborough, Eckington; Nether Birchwood, Alfreton; Newmarket, North Wingfield; Oneston, Dronfield; Over Birchwood, Alfreton; Pentrich; Pinxton; Pye Bridge, Alfreton; Renishaw, Eckington; Riddings, Alfreton; Ripley, Pentrich; Shipley, Heanor; Shirland; Somercotes, Alfreton; South Normanton; Spinkhill, Eckington; Stanfrey, Bolsover; Stanton-by-Dale; Staveley; Sutton, Scarsdale; Swanwick, Alfreton; Tapton, Chesterfield; Troway, Eckington; Tupton, North Wingfield; Wales (Yorkshire); Walton, Chesterfield; West-Hallam; Whittington; Wingerworth, Chesterfield and Woodthorp(e) North Wingfield.
As well as ironstone and the above, other minerals were sometimes worked along with the coal, such as sandstone, various binds, brick clay, cank stone, clunch, fireclay, ganister or crow stone, clay, marl, potters’ clay, paving stones, peacock coal, grindstones and shale to name a few.