OR/13/006 Mineralogy - Revision history

Ajhil: /* Silica cementing and silcrete */

2021-08-16T12:03:36Z

Silica cementing and silcrete

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	\| Herts.		\| Herts.

	\| Whitaker, 1899<ref name="Whitaker 1899">WHITAKER, W. 1899. The geology and other work in Hertfordshire. ''Transactions of the Hertfordshire Natural History Society and Field Club'', '''10''', 105–118.</ref>		\| Whitaker, 1899<ref name="Whitaker 1899">WHITAKER, W. 1899. The geology and other work in Hertfordshire. ''Transactions of the Hertfordshire Natural History Society and Field Club'', '''10''', 105–118. </ref>
	\| Conglomerate ''In situ''		\| Conglomerate ''In situ''
	\|- style="vertical-align:top;"		\|- style="vertical-align:top;"

Ajhil: /* Silica cementing and silcrete */

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Silica cementing and silcrete

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	\| High Wycombe, Bucks		\| High Wycombe, Bucks

	\| Sherlock ''et al''. 1922<ref name="Sherlock 1922">SHERLOCK, R L. 1922. The geology of the country around ~~Aylesbury and Hemel Hempstead~~. ''Memoir of the British Geological Survey (England and Wales)'', sheet ~~238,~~ British Geological Survey, Keyworth, Nottingham, UK. </ref>		\| Sherlock ''et al''. 1922<ref name="Sherlock 1922">SHERLOCK, R L, NOBLE, A H, and PRINGLE, A H. 1922. The geology of the country around Beaconsfield. ''Memoir of the British Geological Survey (England and Wales)'', sheet 255. British Geological Survey, Keyworth, Nottingham, UK.</ref>
	\|		\|

Ajhil: /* London Basin */

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London Basin

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	The Shotley Borehole (Figure 3.10) contains about 3.3 m of Upnor Formation and the five analyses is dominated by smectite with minor illite and kaolin, which is not present in the lower part of the formation. Smectite content peaks near the top of the Upnor Formation where is comprises nearly all the clay minerals. The Reading Formation is 11.7 m thick and the 26 analyses show that illite is the major clay minerals with minor smectite and lesser quantities of kaolin.		The Shotley Borehole (Figure 3.10) contains about 3.3 m of Upnor Formation and the five analyses is dominated by smectite with minor illite and kaolin, which is not present in the lower part of the formation. Smectite content peaks near the top of the Upnor Formation where is comprises nearly all the clay minerals. The Reading Formation is 11.7 m thick and the 26 analyses show that illite is the major clay minerals with minor smectite and lesser quantities of kaolin.

	<u>'''Bradwell Borehole BH202, Bradwell, Essex (BGS borehole TM00NW/27'''</u>, [TM 0053 0851]) (Bloodworth ''et al''., 1987<ref name="Bloodworth 1987">		<u>'''Bradwell Borehole BH202, Bradwell, Essex (BGS borehole TM00NW/27'''</u>, [TM 0053 0851]) (Bloodworth ''et al''., 1987<ref name="Bloodworth 1987">BLOODWORTH, A J, KEMP, S J, INGLETHORPE, S D J, and MORGAN, D J. 1987. Mineralogical and lithochemistry of strata beneath proposed low-level radioactive waste site at Bradwell, Essex; report to Sir William Halcrow and Partners, site investigation consultants. ''British Geological Survey Technical Report'', WG/87/13C.</ref>).

	BLOODWORTH, A J, KEMP, S J, INGLETHORPE, S D J, and MORGAN, D J. 1987. Mineralogical and lithochemistry of strata beneath proposed low-level radioactive waste site at Bradwell, Essex; report to Sir William Halcrow and Partners, site investigation consultants. ''British Geological Survey Technical Report'', WG/87/13C.</ref>).

	The Bradwell Borehole BH202 (Figure 3.10) records about 2.8 m of Upnor Formation comprising a lower 0.7 m of sand and 2.1 m of clay, and 3.2 m of clay from the Upper Mottled Clay (Knox, personal communication, 1997). The lowest part (Upnor Formation) is glauconitic and the clay mineralogy is dominated by smectite with a little illite. Smectite is also the major clay mineral in the lower part of the overlying Reading Formation but illite becomes a more important constituent and kaolinite occurs as a trace clay mineral. In the upper part of the succession, smectite content reduces and illite is the dominant clay mineral with minor quantities of smectite and kaolinite.		The Bradwell Borehole BH202 (Figure 3.10) records about 2.8 m of Upnor Formation comprising a lower 0.7 m of sand and 2.1 m of clay, and 3.2 m of clay from the Upper Mottled Clay (Knox, personal communication, 1997). The lowest part (Upnor Formation) is glauconitic and the clay mineralogy is dominated by smectite with a little illite. Smectite is also the major clay mineral in the lower part of the overlying Reading Formation but illite becomes a more important constituent and kaolinite occurs as a trace clay mineral. In the upper part of the succession, smectite content reduces and illite is the dominant clay mineral with minor quantities of smectite and kaolinite.

Ajhil: /* Detailed clay mineralogy */

2021-08-16T11:59:46Z

Detailed clay mineralogy

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	The Bradwell Borehole BH202 (Figure 3.10) records about 2.8 m of Upnor Formation comprising a lower 0.7 m of sand and 2.1 m of clay, and 3.2 m of clay from the Upper Mottled Clay (Knox, personal communication, 1997). The lowest part (Upnor Formation) is glauconitic and the clay mineralogy is dominated by smectite with a little illite. Smectite is also the major clay mineral in the lower part of the overlying Reading Formation but illite becomes a more important constituent and kaolinite occurs as a trace clay mineral. In the upper part of the succession, smectite content reduces and illite is the dominant clay mineral with minor quantities of smectite and kaolinite.		The Bradwell Borehole BH202 (Figure 3.10) records about 2.8 m of Upnor Formation comprising a lower 0.7 m of sand and 2.1 m of clay, and 3.2 m of clay from the Upper Mottled Clay (Knox, personal communication, 1997). The lowest part (Upnor Formation) is glauconitic and the clay mineralogy is dominated by smectite with a little illite. Smectite is also the major clay mineral in the lower part of the overlying Reading Formation but illite becomes a more important constituent and kaolinite occurs as a trace clay mineral. In the upper part of the succession, smectite content reduces and illite is the dominant clay mineral with minor quantities of smectite and kaolinite.

	<u>'''Wormingford Mere Borehole, BGS Borehole TL93SW/1'''</u> [TL 9267 3262] and Bures Borehole, BGS borehole TQ05SE/2 [TL 9120 3399] (Ellison ''et al''., 1986<ref name="Ellison 1986">ELLISON, R A, and LAKE R D. 1986. Geology of the country around Braintree. ''Memoir of the British Geological Survey, (England and Wales)'', Sheet 223. British Geological Survey, Keyworth, Nottingham, UK.</ref>).		<u>'''Wormingford Mere Borehole, BGS Borehole TL93SW/1'''</u> [TL 9267 3262] and Bures Borehole, BGS borehole TQ05SE/2 [TL 9120 3399] (Ellison ''et al''., 1986<ref name="Ellison 1986">ELLISON, R A, and LAKE R D. 1986. Geology of the country around Braintree. ''Memoir of the British Geological Survey, (England and Wales)'', Sheet 223. British Geological Survey, Keyworth, Nottingham, UK. </ref>).

	The Wormingford Borehole and Bures Borehole (Figure 3.10) record a lower bed (4.4 and 4.5 m thick respectively) comprising green and red mottled glauconitic clayey fine to medium sand of the Upnor Formation. Above is about 5 m predominantly of stiff to very stiff, red to purple, with vertical veining and mottles of orange and pale greyish blue clay with silt beds and sandy silt beds of the Reading Formation. The clay assemblage of the Upnor Formation is dominated by smectite, which becomes significantly less abundant in the overlying Reading Formation where illite is the dominant clay mineral. Kaolinite, rarely present in the Upnor Formation, becomes more common further up the Reading Formation succession, in conjunction with decreasing smectite.		The Wormingford Borehole and Bures Borehole (Figure 3.10) record a lower bed (4.4 and 4.5 m thick respectively) comprising green and red mottled glauconitic clayey fine to medium sand of the Upnor Formation. Above is about 5 m predominantly of stiff to very stiff, red to purple, with vertical veining and mottles of orange and pale greyish blue clay with silt beds and sandy silt beds of the Reading Formation. The clay assemblage of the Upnor Formation is dominated by smectite, which becomes significantly less abundant in the overlying Reading Formation where illite is the dominant clay mineral. Kaolinite, rarely present in the Upnor Formation, becomes more common further up the Reading Formation succession, in conjunction with decreasing smectite.

Ajhil: /* Calcium carbonate and calcrete */

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Calcium carbonate and calcrete

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	====Calcium carbonate and calcrete====		====Calcium carbonate and calcrete====
	Calcium carbonate nodules are present in parts of the Upnor and Reading formations. They coalesce into more coherent cemented beds (calcrete) up to 1.6 m thick in the Upnor Formation, where the overlying Lower Mottled Clay is thin, and in the Lower Mottled Clay in central and east London. Calcareous nodules are also seen near Arundel in the Hampshire Basin. In east London calcite veins are present in the clays of the Lower Mottled Clay and described in ground investigation reports as very weak to weak mottled green-grey, purple grey and brown mudstone. The calcretes and calcareous nodules vary between very weak to moderately strong, brown, light grey brown, bluish-grey, grey or white, sometimes crystalline limestone. Calcretes may have been more widespread and a possible precursor to silcretes such as the Hertfordshire puddingstones, which were then altered to silcretes as conditions changed (Skipper, 1999<ref name="Skipper 1999">SKIPPER, J. 1999. The stratigraphy of the Lambeth Group (Palaeocene) of South East England. PhD. Thesis. Imperial College, London, and Natural History Museum. </ref>).		Calcium carbonate nodules are present in parts of the Upnor and Reading formations. They coalesce into more coherent cemented beds (calcrete) up to 1.6 m thick in the Upnor Formation, where the overlying Lower Mottled Clay is thin, and in the Lower Mottled Clay in central and east London. Calcareous nodules are also seen near Arundel in the Hampshire Basin. In east London calcite veins are present in the clays of the Lower Mottled Clay and described in ground investigation reports as very weak to weak mottled green-grey, purple grey and brown mudstone. The calcretes and calcareous nodules vary between very weak to moderately strong, brown, light grey brown, bluish-grey, grey or white, sometimes crystalline limestone. Calcretes may have been more widespread and a possible precursor to silcretes such as the Hertfordshire puddingstones, which were then altered to silcretes as conditions changed (Skipper, 1999<ref name="Skipper 1999">SKIPPER, J. 1999. The stratigraphy of the Lambeth Group (Palaeocene) of South East England. PhD. Thesis. Imperial College, London, and Natural History Museum.</ref>).

	Core from the Jubilee Line Extension (BH JLE 404T) contained two zones of calcrete, one near the top of the Upnor Formation and the other in the Lower Mottled Clay, which is about 1.30 m thick. The calcrete in the Upnor Formation is about 0.30 m thick as shown in Figure 3.17.		Core from the Jubilee Line Extension (BH JLE 404T) contained two zones of calcrete, one near the top of the Upnor Formation and the other in the Lower Mottled Clay, which is about 1.30 m thick. The calcrete in the Upnor Formation is about 0.30 m thick as shown in Figure 3.17.

Ajhil: /* Pedogenic alteration */

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Pedogenic alteration

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	[[Image:OR13006fig3.15.jpg\|thumb\|center\|500px\| '''Figure 3.15'''    Root channel infilled with sand with clay particles oriented around channel wall. Upnor Formation, Newbury Bypass, 1.5 m above Chalk. (BGS photomicrograph No. E431S1/04). ]]		[[Image:OR13006fig3.15.jpg\|thumb\|center\|500px\| '''Figure 3.15'''    Root channel infilled with sand with clay particles oriented around channel wall. Upnor Formation, Newbury Bypass, 1.5 m above Chalk. (BGS photomicrograph No. E431S1/04). ]]

	This sequence is repeated many times. The oxidation of pyrite may occur during any subsequent phase of emergence. Different minerals are produced by different rates of oxidation. Hydroxides are produced by slow oxidation and jarosite during rapid oxidation. The dominance of pseudogley features indicates terrestrial conditions. This sequence probably originated in an environment of intermittent sedimentation and soil formation. Most of the beds of the Reading Formation at Alum Bay show alteration due to pedogenesis, indicating that for most of the time the soil formation kept pace with sedimentation and that sedimentation was slow. The soils also show a pattern of increasing degrees of soil development that occurred during periods of falling base level/water table. These soils were probably deposited as overbank fines in a floodplain environment. They were seasonally waterlogged but as the water table or base level fell, leading to increasing emergence, a degree of soil development occurred (Skipper, 1999<ref name="Skipper 1999"></ref>).		This sequence is repeated many times. The oxidation of pyrite may occur during any subsequent phase of emergence. Different minerals are produced by different rates of oxidation. Hydroxides are produced by slow oxidation and jarosite during rapid oxidation. The dominance of pseudogley features indicates terrestrial conditions. This sequence probably originated in an environment of intermittent sedimentation and soil formation. Most of the beds of the Reading Formation at Alum Bay show alteration due to pedogenesis, indicating that for most of the time the soil formation kept pace with sedimentation and that sedimentation was slow. The soils also show a pattern of increasing degrees of soil development that occurred during periods of falling base level/water table. These soils were probably deposited as overbank fines in a floodplain environment. They were seasonally waterlogged but as the water table or base level fell, leading to increasing emergence, a degree of soil development occurred (Skipper, 1999<ref name="Skipper 1999">SKIPPER, J. 1999. The stratigraphy of the Lambeth Group (Palaeocene) of South East England. PhD. Thesis. Imperial College, London, and Natural History Museum.</ref>).

	===Hard bands===		===Hard bands===

Ajhil: /* Hampshire Basin */

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Hampshire Basin

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	''Coastal sites''<br><u>'''Studland Bay, Dorset'''</u> [SZ 044 824] (Gilkes, 1966<ref name="Gilkes 1966"></ref>, 1968<ref name="Gilkes 1968"></ref>)		''Coastal sites''<br><u>'''Studland Bay, Dorset'''</u> [SZ 044 824] (Gilkes, 1966<ref name="Gilkes 1966"></ref>, 1968<ref name="Gilkes 1968"></ref>)
	The lower part of the Lambeth Group at Studland Bay was studied by (Gilkes, 1966<ref name="Gilkes 1966"></ref>, 1968<ref name="Gilkes 1968"></ref>). This part of the sequence equates to the basal fluvial glauconitic sands (possibly reworked Upnor Formation) and iron cemented sands, pedogenically altered sands and silts and fluvial channel sands, Lower Mottled Clay (Skipper, 1999<ref name="Skipper 1999"></ref>). The lower fluvial sands contain approximately equal quantities of smectite, illite and kaolinite. Smectite is the main clay mineral at the base of the pedogenically altered sands and silts with minor illite and kaolinite. However, in the upper part of these silts the clay mineralogy is similar to the basal beds. In the lower part of the fluvial channel sands the only reported clay mineral is mixed layer illite-smectite. The rest of these sands comprise illite and kaolinite with trace or no detectable smectite.		The lower part of the Lambeth Group at Studland Bay was studied by (Gilkes, 1966<ref name="Gilkes 1966"></ref>, 1968<ref name="Gilkes 1968"></ref>). This part of the sequence equates to the basal fluvial glauconitic sands (possibly reworked Upnor Formation) and iron cemented sands, pedogenically altered sands and silts and fluvial channel sands, Lower Mottled Clay (Skipper, 1999<ref name="Skipper 1999">SKIPPER, J. 1999. The stratigraphy of the Lambeth Group (Palaeocene) of South East England. PhD. Thesis. Imperial College, London, and Natural History Museum.</ref>). The lower fluvial sands contain approximately equal quantities of smectite, illite and kaolinite. Smectite is the main clay mineral at the base of the pedogenically altered sands and silts with minor illite and kaolinite. However, in the upper part of these silts the clay mineralogy is similar to the basal beds. In the lower part of the fluvial channel sands the only reported clay mineral is mixed layer illite-smectite. The rest of these sands comprise illite and kaolinite with trace or no detectable smectite.

	'''<u>Whitecliff Bay, Isle of Wight</u>''' [SZ 4639 8580 to 4639 8585] (Gilkes, 1966<ref name="Gilkes 1966"></ref>, 1968<ref name="Gilkes 1968"></ref>; Huggett and Knox, 2006<ref name="Huggett 2006"></ref>).		'''<u>Whitecliff Bay, Isle of Wight</u>''' [SZ 4639 8580 to 4639 8585] (Gilkes, 1966<ref name="Gilkes 1966"></ref>, 1968<ref name="Gilkes 1968"></ref>; Huggett and Knox, 2006<ref name="Huggett 2006"></ref>).

Ajhil: /* London basin */

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London basin

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	The simple models of clay mineral distribution described above are general trends. Due to the complex nature of the deposition, pedogenic alteration and the tectonic and volcanic activity during the late Palaeocene detailed studies have shown rapid local and possible regional changes. A good example is Alum Bay, described by Gilkes (1966<ref name="Gilkes 1966"></ref>, 1968<ref name="Gilkes 1968"></ref>), Buurman (1980)<ref name="Buurman 1980"></ref> and Pearce (1998)<ref name="Pearce 1998"></ref>. Investigating the clay mineralogy of the early Tertiary of the Hampshire Basin, Gilkes (1966<ref name="Gilkes 1966"></ref>, 1968<ref name="Gilkes 1968"></ref>), and analysed nine samples from the cliff section and found them to contain mainly illite and kaolinite with minor or trace smectite. Buurman (1980)<ref name="Buurman 1980"></ref>, studying pedogenesis, analysed forty-five samples including at least one sample from each identifiable bed, apart from the basal unit which was obscured at the time. Most of the results showed a clay mineral assemblage of illite and kaolinite. However, a marked contrast in clay mineralogy occurs within a few metres of the top of the lower Reading Formation. Here, a two to three metre thick mottled clay bed contains increasing quantities of smectite that becomes the dominant clay mineral at the top of the bed. At the top of the Lower Mottled Clay kaolinite is the dominant clay mineral. More recent analysis of samples from this section for this project (Pearce ''et al''., 1998<ref name="Pearce 1998"></ref>) showed a similar smectite peak. A smectite peak also occurs near the top of the Lower Mottled Clay in Central London (Knox, personal communication, 1997).		The simple models of clay mineral distribution described above are general trends. Due to the complex nature of the deposition, pedogenic alteration and the tectonic and volcanic activity during the late Palaeocene detailed studies have shown rapid local and possible regional changes. A good example is Alum Bay, described by Gilkes (1966<ref name="Gilkes 1966"></ref>, 1968<ref name="Gilkes 1968"></ref>), Buurman (1980)<ref name="Buurman 1980"></ref> and Pearce (1998)<ref name="Pearce 1998"></ref>. Investigating the clay mineralogy of the early Tertiary of the Hampshire Basin, Gilkes (1966<ref name="Gilkes 1966"></ref>, 1968<ref name="Gilkes 1968"></ref>), and analysed nine samples from the cliff section and found them to contain mainly illite and kaolinite with minor or trace smectite. Buurman (1980)<ref name="Buurman 1980"></ref>, studying pedogenesis, analysed forty-five samples including at least one sample from each identifiable bed, apart from the basal unit which was obscured at the time. Most of the results showed a clay mineral assemblage of illite and kaolinite. However, a marked contrast in clay mineralogy occurs within a few metres of the top of the lower Reading Formation. Here, a two to three metre thick mottled clay bed contains increasing quantities of smectite that becomes the dominant clay mineral at the top of the bed. At the top of the Lower Mottled Clay kaolinite is the dominant clay mineral. More recent analysis of samples from this section for this project (Pearce ''et al''., 1998<ref name="Pearce 1998"></ref>) showed a similar smectite peak. A smectite peak also occurs near the top of the Lower Mottled Clay in Central London (Knox, personal communication, 1997).

	Rapid changes in the clay mineral assemblage occur elsewhere. At the Lower Upnor Quarry [TQ 757 712] and Orsett Pit [TQ 673 808] the typically smectite-rich Upnor Formation contains a kaolinite-rich zone associated with a palaeosol horizon. In the lower Reading Formation at the Newbury Bypass section the clay minerals change from smectite-rich to kaolinite-rich or illite-rich and smectite-poor within a few metres (Skipper, 1999<ref name="Skipper 1999"></ref>; Pearce ''et al''., 1998<ref name="Pearce 1998"></ref>).		Rapid changes in the clay mineral assemblage occur elsewhere. At the Lower Upnor Quarry [TQ 757 712] and Orsett Pit [TQ 673 808] the typically smectite-rich Upnor Formation contains a kaolinite-rich zone associated with a palaeosol horizon. In the lower Reading Formation at the Newbury Bypass section the clay minerals change from smectite-rich to kaolinite-rich or illite-rich and smectite-poor within a few metres (Skipper, 1999<ref name="Skipper 1999">SKIPPER, J. 1999. The stratigraphy of the Lambeth Group (Palaeocene) of South East England. PhD. Thesis. Imperial College, London, and Natural History Museum.</ref>; Pearce ''et al''., 1998<ref name="Pearce 1998"></ref>).

	In the Hampshire Basin, the Bunker’s Hill Borehole [SU 3038 1498] contained a very unusual clay mineral assemblage about 3 m above the Upnor Formation, consisting of halloysite with random mixed-layer chlorite-vermiculite and chlorite-smectite.		In the Hampshire Basin, the Bunker’s Hill Borehole [SU 3038 1498] contained a very unusual clay mineral assemblage about 3 m above the Upnor Formation, consisting of halloysite with random mixed-layer chlorite-vermiculite and chlorite-smectite.

Ajhil: /* Gypsum */

2021-08-16T11:55:52Z

Gypsum

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	[[Image:OR13006fig3.8.jpg\|thumb\|center\|400px\| '''Figure 3.8'''    Pseudomorphs after gypsum in the Lower Shelly Beds at Newhaven [TQ 7590 7110]. ]]		[[Image:OR13006fig3.8.jpg\|thumb\|center\|400px\| '''Figure 3.8'''    Pseudomorphs after gypsum in the Lower Shelly Beds at Newhaven [TQ 7590 7110]. ]]

	Although gypsum is most likely to form in parts of the Woolwich and Upnor formations it has been seen where reworked calcareous nodules mix with lignite, for instance at the mid-Lambeth Group Hiatus at Alum Bay (Skipper 1999<ref name="Skipper 1999"></ref>).		Although gypsum is most likely to form in parts of the Woolwich and Upnor formations it has been seen where reworked calcareous nodules mix with lignite, for instance at the mid-Lambeth Group Hiatus at Alum Bay (Skipper 1999<ref name="Skipper 1999">SKIPPER, J. 1999. The stratigraphy of the Lambeth Group (Palaeocene) of South East England. PhD. Thesis. Imperial College, London, and Natural History Museum.</ref>).

	==Clay mineralogy==		==Clay mineralogy==

Ajhil: /* Gypsum */

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Gypsum

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	Sulphuric acid + Calcium carbonate® Gypsum + water + carbon dioxide H<sub>2</sub>SO<sub>4</sub> + CaCO<sub>3</sub> + 2H<sub>2</sub>O ® CaSO<sub>4</sub>.2H<sub>2</sub>O + H<sub>2</sub>O + CO<sub>2</sub> (2)		Sulphuric acid + Calcium carbonate® Gypsum + water + carbon dioxide H<sub>2</sub>SO<sub>4</sub> + CaCO<sub>3</sub> + 2H<sub>2</sub>O ® CaSO<sub>4</sub>.2H<sub>2</sub>O + H<sub>2</sub>O + CO<sub>2</sub> (2)

	Gypsum may have formed as a part of the sub-tropical weathering process shortly after deposition but, because it is soluble, would have been removed from the near surface by water movement. It is rarely described in the Lambeth Group and there are only a few references to gypsum in the BGS National Geotechnical Properties Database, all associated with the Lower Shelly Clay. In cliffs at Newhaven, Skipper (1999)<ref name="Skipper 1999"></ref> describes gypsum in a thick lignitic clay bed about 0.80 m above yellow (jarositic) very sandy clay (Figure 3.8). In a section exposed in the Upnor Brick and Stone Quarry at Lower Upnor in Kent [TQ 7590 7110], a lignitic bed at the base of the Woolwich Formation Lower Shelly Clay contains occasional shell moulds and abundant gypsum as selenite crystals. It is likely that these parts of the bed were originally shelly and have now been replaced by the gypsum.		Gypsum may have formed as a part of the sub-tropical weathering process shortly after deposition but, because it is soluble, would have been removed from the near surface by water movement. It is rarely described in the Lambeth Group and there are only a few references to gypsum in the BGS National Geotechnical Properties Database, all associated with the Lower Shelly Clay. In cliffs at Newhaven, Skipper (1999)<ref name="Skipper 1999">SKIPPER, J. 1999. The stratigraphy of the Lambeth Group (Palaeocene) of South East England. PhD. Thesis. Imperial College, London, and Natural History Museum.</ref> describes gypsum in a thick lignitic clay bed about 0.80 m above yellow (jarositic) very sandy clay (Figure 3.8). In a section exposed in the Upnor Brick and Stone Quarry at Lower Upnor in Kent [TQ 7590 7110], a lignitic bed at the base of the Woolwich Formation Lower Shelly Clay contains occasional shell moulds and abundant gypsum as selenite crystals. It is likely that these parts of the bed were originally shelly and have now been replaced by the gypsum.

	[[Image:OR13006fig3.8.jpg\|thumb\|center\|400px\| '''Figure 3.8'''    Pseudomorphs after gypsum in the Lower Shelly Beds at Newhaven [TQ 7590 7110]. ]]		[[Image:OR13006fig3.8.jpg\|thumb\|center\|400px\| '''Figure 3.8'''    Pseudomorphs after gypsum in the Lower Shelly Beds at Newhaven [TQ 7590 7110]. ]]