Upload
others
View
0
Download
0
Embed Size (px)
Citation preview
Identifying the “blue substance” at the Roman site of
Vindolanda, Northumberland
Taylor, G1*, Hefford, RJW2, Birley, A3, Huntley JP4
1. School of Science, Engineering and Design, Teesside University, Middlesbrough, TS1 3BA.2. c/o School of Science, Engineering and Design, Teesside University, Middlesbrough, TS1 3BA.
3. Vindolanda, Bardon Mill, Hexham, Northumberland NE47 7JN.4. Department of Archaeology, Durham University, Durham DH1 3LE
*corresponding author, [email protected]
Keywords: Vindolanda, Vivianite, Preservation, Anaerobic, Iron
Abstract: Archaeological landscapes and environments are extremely complex and
diverse systems. Vindolanda, situated in Northumberland, UK, is part of the Frontiers
of the Roman Empire World Heritage site and has remarkable preservation of
artefacts of international significance including leather, writing tablets and bones.
Vindolanda is a waterlogged site and contains anoxic layers which, it is postulated,
aids in the preservation of these important artefacts. The anoxic layers contain many
chemical and microbiological properties which vary from context to context,
depending on what remains in the soil and what is introduced into the archaeological
environment through continued post-depositional processes. During excavations at
Vindolanda, as at other sites the presence of a ‘blue substance’ has been noted by
researchers for many years. This ‘blue substance’ has been generally described in
the literature as Vivianite (hydrated iron (II) phosphate), and has speculatively been
used as a signature of good organic preservation in archaeological contexts. In this
paper, a range of analytical instrumentation SEM-EDX and XRD has been used to
characterise the blue substance, taken from one well defined context to confirm as
Vivianite (Fe3(PO4)2.8H2O).
1. Introduction
The archaeological site of Vindolanda, situated in Northumberland is part of the
Frontiers of the Roman Empire World Heritage Site. The anoxic layers have
produced some of the most remarkable artefacts from the Roman world, such as the
Vindolanda ink on wood writing tablets, thousands of leather boots and shoes and
Page 1 of 17
even the preservation of fine textiles and other organic remains which seldom
survive in the archaeological record (Birley 2009). A common visual observation of
this exemplary preservation at Vindolanda has been the near constant presence of a
distinctive ‘blue substance’ which has been postulated as Vivianite. Although,
Vivianite has been recognised at archaeological sites its chemical and/or
microbiological formation has not been investigated in exhaustive detail within an
archaeological context (McGowan and Prangnell 2006). Thus, several questions
arise including under what conditions is Vivianite formed? What particular chemical
properties of soil are required? What microbiological processes are important
considerations? Furthermore, and most importantly what do the chemical and
biological properties tell us about the wider archaeological environment and post-
depositional processes in order to aid in the preservation and management of
important archaeological sites?
It is believed that understanding the complex chemical and microbiological
processes that impact upon the formation of Vivianite is essential to gain a more
nuanced appreciation of preservation mechanisms that take place on waterlogged
archaeological sites. Further understanding of preservation processes for artefacts
and the future care and management of precious, irreplaceable archaeological
resources and environments is crucial at Vindolanda and other World Heritage Sites.
Furthermore, it is hoped that a more comprehensive knowledge of preservation
processes will aid the understanding of effects due to land use and climate change
over time. After an explanation of the site formation processes the paper will explore
the most fundamental objective – characterising the “blue substance” that is often
observed within the deeper layers of archaeological deposition at Vindolanda.
1.1 Vindolanda
Vindolanda is a Roman archaeological site located on the Stanegate road from
Corbridge to Carlisle just south of Hadrian’s Wall in Northumberland, UK, see Figure
1.0.
Page 2 of 17
Figure 1.0:- Geographical location of the Roman Archaeological Site of Vindolanda,
Northumberland, United Kingdom. (Reprinted with permission of The Vindolanda
Trust).
The first Roman construction at Vindolanda predates Hadrian’s Wall and comprised
Roman auxiliary forts with associated extramural settlements, occupied from c
AD80-85 until the end of the Roman occupation and beyond (perhaps upto the end
of the 8th century) (Birley 2009). During its long history structures at Vindolanda were
repeatedly, demolished and reconstructed in a wide variety of different forms as the
garrisons and their requirements changed with time. Initially the forts were built in
timber (at least 6 wooden forts) but latterly in stone (at least 3 stone forts). As a
result of the rebuilding process, earliest occupational layers at Vindolanda are often
several metres deep with the last upper periods of use of the site, from the 3 rd
century onwards, generally exposed to a very different chemical and microbiological
environment as well as (until the 1930’s) damage such as ploughing and stone
robbing (Birley 2009).
The site is bordered by streams in small valleys to the north, east and south with
ground water coming down the hill mainly from the west appearing as springs. At a
number of points and in times of reasonable rainfall springs appear from the slope
and exhibit a red brown colouration with an associated “oily” sheen. A relatively
small plateau, located on the east side of the site, is bordered to the immediate west
by a depression in the ground. This depression was “in filled” regularly during the
occupation period. Most of the larger forts were built across this depression and
onwards up a gentle slope which moves upwards to the west. The remains of the
last stone fort can be seen today on the plateau and represent a small fort however,
Page 3 of 17
size, precise location and design of the stone forts varied with time over the lengthy
occupation of the site.
Figure 2.0: Aerial photograph of the Roman Site of Vindolanda (Reprinted with
permission of The Vindolanda Trust).
Due to the often-inclement weather of Northumberland, underlying geology and
geographical position Vindolanda can be very wet (Birley 2009). As a result,
occupants generally raised foundations of buildings when each new fort was
constructed. This repeated process coupled with a combination of Roman building
techniques, especially demolition followed by covering the site with clay and then turf
prior to rebuilding, resulted in Vindolanda becoming a layered cake of occupation.
Thus, occupational layers are often separated by largely impervious layers of
boulder clay. Importantly the clay layers are extremely effective at sealing out
oxygen (and probably oxygenated water) resulting in exceptional preservation of
organic and metallic artefacts (Birley 2009). In the deeper and usually anoxic layers
at Vindolanda it is very noticeable that a scattered blue colouration starts to appear
within a few hours of opening up an area and this can form on metallic and organic
as well as inorganic objects. It has long been assumed that the blue colouration was
due to Vivianite (Birley., per comms).
Page 4 of 17
1.2 Vivianite
Vivianite is unusual being a striking blue colouration (Read 1970) and thus distinctive
in an excavation environment. For the purposes of this short note paper Vivianite
(which is white in its anoxic form) is hydrated iron (II) phosphate (Fe3(PO4)2.8H2O)
which undergoes surface oxidation in the presence of light to create a mixed iron
(II)/iron (III) material. Once excavated and upon continued exposure the blue
colouration will progressively darken and may end up as amorphous iron (III)
phosphate, which is white/yellow in appearance. The nomenclature of the various
iron phosphates ranging from pure iron (II) progressively through to pure iron (III) is
somewhat confusing and the subject of some debate (Rodgers 1986). The terms
Vivianite, Metavivianite and Kerchenite are used loosely and it is not always clear
exactly what chemical composition is under discussion. This confusion is
compounded by the substitution of other elements (e.g. Manganese, Calcium and
Magnesium) into the material when formed in natural environments (Kloprogge et al.,
2003). The chemistry of iron in its two common oxidation states is extremely complex
and outside the scope of this short note paper however, it should be noted that many
other iron compounds can be formed, especially during the preservation of
archaeological artefacts (Wang 2007). For example, within the soil and in the
presence of excess oxygen and water, metallic iron will oxidise to the iron (III) form
and creates the familiar ‘rust’ orange/red colouration (Read 1970). Iron redox
processes under anoxic and reducing conditions are complex, involving abiotic
chemical reactions and/or microbiologically mediated processes (Melton et al.,
2014).
1.3 Vivianite and preservation
Iron artefacts from Hungate, York, UK showed a surprising lack of corrosive effects
despite being in waterlogged and anoxic conditions (Farrer et al., 1953). The lack of
corrosion was attributed to the inhibition of the activity of sulphate reducing
bacterium (Desulfovibrio desulfuricans) caused by the high concentration of tannates
in the soil (Farrer et al., 1953). Thus, the production of hydrogen sulphide, one of the
main causative compounds responsible for corrosion and deterioration of artefacts,
was not formed (Farrer et al., 1953). Furthermore, within the soil the presence of a
blue substance resembling Vivianite was noted (Farrer et al., 1953). Laboratory
Page 5 of 17
experiments using apparently corrosive soil further explored the role of Vivianite in
preservation (Booth et al., 1962). Booth (1962) demonstrated that nails coated with
Vivianite were less susceptible to corrosion, by restricting movement of ions in
solution (Booth et al., 1962). Although, the exact mechanisms of the role of Vivianite
in preservation of archaeological artefacts is still poorly understood, it is clear that
strict chemical and microbiological conditions must be present for Vivianite formation
(Rothe et al., 2016 Nanzyo et al., 2010).
This paper is the first stage of a wider and more comprehensive study into the
chemical and microbiological preservation processes at the Roman Site of
Vindolanda, Northumberland UK. Thus, understanding and unravelling the complex
chemical and microbiological processes that impact on the formation of Vivianite is
essential to gain a more nuanced appreciation of preservation mechanisms that take
place on archaeological sites. Preservation and not least the future care and
management of precious archaeological resources and environments are essential.
Furthermore, comprehensive knowledge of preservation processes will aid the
understanding of effects due to climate change and land use over time.
2. Method
2.1 Sample origin
During the excavation season (April to September 2016) at Vindolanda,
Northumberland, UK a range of samples were collected – the criterion for collection
was visual identification of a blue substance on the exterior of the artefact and/or
material. One sample was selected for analysis, as determined by the appearance of
a blue substance on a section of a rampart (see Figure 3.0) and collected for further
analysis. This rampart formed part of the internal packing against the southern wall
of stone fort 2 above the demolished wall of stone fort 1. The rampart was
constructed using turfs with these subsequently decaying to leave behind the mineral
components. The rampart contained (in parts) a blue substance which upon visual
inspection, comprised both individual conglomerates (of up to 1 or 2 mm in diameter)
and longer inclusions (a few cm in length and a few mm in width and depth). The
blue substance was physically extracted using a pair of tweezers.
Page 6 of 17
Figure 3.0 The rampart sample containing an approximately 1-2mm thick layer of
blue substance.
2.2 Scanning electron microscopy (SEM) and energy dispersive X-ray analysis
(EDX)
Sampling was undertaken along the long blue inclusion shown in Figure 3, and
analysed for morphology and chemical composition using a Hitachi VP S-3400N
SEM coupled with an Oxford Instruments EDX. The system was controlled by
OMNIC 7.3 software. Analysis was carried out in variable pressure mode, eliminating
the need of any coating contamination.
2.3 X-Ray Diffraction
X-ray diffraction measurements were undertaken by Dr Chris Pask in the School of
Chemistry, University of Leeds using a Bruker D2 Phaser Diffractometer with Cu
radiation (1.54060 Å) between 5 and 50° 2θ. XRD traces were analysed by Ms
Lesley Neve in the School of Earth and Environmental Sciences at the University of
Page 7 of 17
Leeds using the ICDD database and standard data from card number PDF 30-662
for Vivianite.
3. Results
The rampart sample was used to conduct the analyses of the ‘blue substance’ in this
study. As stated above the blue encrustations formed individual conglomerates (of
up to 1 or 2 mm in diameter) and longer inclusions (a few cm in length and a few mm
in width and depth). Image shown in Figure 3.0.
3.1 Microscopic analysis
The determination of the ‘blue substance’ was initially screened using low and high
power microscope analysis. The size and shape of the inclusions were not uniform
but rather a set of closely packed blue and off-white crystals. The results were
consistent with other previous published studies and geological literature for Vivianite
morphology (Read 1970). Scanning electron microscopy (SEM) analysis showed the
‘blue encrustations’ were distinct flat, monoclinic and oblong crystals of varying
sizes, the size of a typical large crystal was approximately 160 x 75 microns (Figure
4.0), the above morphology was consistent with published literature for Vivianite
(Read 1970)
3.2 SEM-EDX
SEM-EDX analysis of the blue encrustation from the rampart sample was performed.
The observed structural morphology was described above, see Figure 4.0, a (Egger
et al., 2015; O’Connell et al., 2015). A summary of the EDX results is shown in Table
1.0. and spectra provided in Figure 4.0, b. Iron and phosphorus were abundant in all
the samples. Silica, aluminium and manganese were present at much lower
concentrations. Aluminium and silica are present but thought to be due to impurities
from the soil. The morphology and elemental composition of the blue encrustation is
consistent with the published literature to confirm the presence of the blue
encrustations is Vivianite (Rothe et al., 2014; Rothe et al., 2016).
Page 8 of 17
Figure 4.0:- Physical and chemical properties of vivianite taken from the rampart
sample
a) Morphology
b) Elemental composition
Page 9 of 17
Table 1:- EDX results obtained from six blue encrustations samples from the rampart
sample. (data given as weight %).
Element O Fe P Mn Si AlVivianite 32.74 49.10 18.12 - - -Vivianite Rothe et al., 2014
- 43.0 23.50 3.3 - 3.4
Soil vivianiteKloprogge et al., 2003
- 51.33 41.25 2.61
Sample 1 45.34 41.44 8.31 0.36 3.01 1.27Sample 2 45.01 40.06 8.29 - 3.02 1.42Sample 3 47.56 39.58 11.36 - 0.74 0.38Sample 4 31.00 51.07 1.28 - 5.53 2.94Sample 5 23.36 33.95 0.13 0.19 3.70 1.65
Sample average (n=5) 38.45 41.22 5.87 0.28 3.20 1.53
Sample standard deviation (n=5) 10.69 6.20 4.90 0.12 1.72 0.92
3.3 XRD
The XRD trace was performed on a small sample obtained from the rampart sample.
The XRD trace showed approximately fifteen peaks which correlated with published
XRD data for Vivianite (Sameshima et al., 1985 ; ICCD card number PDF 30-0662).
Additional peaks could be seen and two of these correlated with published data for
quartz with one peak remaining unidentified. It is not surprising to find quartz
present as rounded granules containing silicon and oxygen are also observed by
SEM-EDX (Rothe et al., 2016).
Page 10 of 17
Vivanite Sample
Quartz standard
Literature standard
Figure 5.0 XRD trace from the rampart sample a) Black line - blue encrustation from rampart samples simulated pattern b) Blue line - literature standard single vivianite crystal (Ref ICSD 423390).
This combination of low powdered microscopy, elemental analysis by FTIR-ATR,
SEM-EDX and XRD can confirm that the blue encrustations separated from a
rampart sample is an iron (II) phosphate known as Vivianite.
4. Discussion
This study is the first of a series of ongoing investigations to articulate the biological
and chemical environment at Vindolanda in order to aid our understanding of
preservation processes for valuable artefacts. A combination of analytical techniques
including SEM-EDX and XRD have been used to study the compositional and
microscopic structure of a ‘blue substance’ from a rampart sample. The observations
and results confirm that the ‘blue encrustations’ located in the rampart sample can
be identified as Vivianite. Although, the rampart sample appeared to contain the
“purest” sample of the Vivianite it also contained quartz and other soil contaminants.
Page 11 of 17
The atomic percentages as determined by SEM-EDX indicated that the flat, oblong
crystal samples contained the elements and percentage composition of iron,
phosphorus and oxygen to be indicative of Vivianite. The size and morphology of the
crystals by both optical microscopy and SEM were comparable and matched to that
found in the published literature (Read 1970: Rothe et al., 2016). Many other
elements were also determined in small concentrations including silicon, calcium,
cobalt, manganese and aluminium. It was not surprising to find a small concentration
of manganese present as manganese can substitute for iron within the Vivianite
structure (Kloprogge et al., 2003). However, the small concentrations of calcium,
aluminium and silicon probably originate from the post-depositional environment. It
must be stated that a higher level of oxygen than expected from Vivianite alone and
a high level of carbon were also determined although, due to the nature of the EDX
technique the level of carbon (and oxygen) is likely to be over-estimated. At its
simplest the carbon and oxygen could be accounted for by the presence of
carbonate, acetate or related species. Alternatively, it is possible that polyphenols
(tannins) are also present at low concentration in the rampart sample (Farrer et al.,
1953).
The role and importance of Vivianite in these waterlogged environments should not
be underestimated. Firstly, the chemical characteristics of Vivianite means that it
acts as a buffer, maintaining steady-state conditions in anoxic sediments
(Walpersdorf et al., 2013) regulating and controlling phosphate concentration and
release within the environment and thus impacting on the preservation of artefacts
(Maritan and Mazzoli 2004). It has also been repeatedly reported that Vivianite is an
important sink for phosphate in coastal and lake sediments (Egger et al., 2015; Li et
al., 2012; O’Connell et al., 2015; Rothe et al., 2014, 2016). Subsequent
investigations will address the questions of why the chemical conditions at
Vindolanda (at least in some locations) appear to be favourable to the formation of
the Vivianite. Secondly, microbiological characterisation will seek to understand the
importance of sulphate reducing bacteria, Vivianite and preservation towards
artefacts (Farrer et al., 1953). Iron artefacts often corrode due to the metabolic action
of the bacteria producing hydrogen sulphide. However, under anoxic conditions
certain types of micro-organisms known as dissimilatory metal reducing bacteria
(DMRBs), can be active and these facultative micro-organisms use iron (III) as the
Page 12 of 17
terminal electron acceptor (when oxygen is in short supply) thus creating iron (II) (Li
et al., 2012). Thus, Vivianite is formed in anoxic layers due to the presence of iron
(III), phosphate and DMRB’s in the absence (or low levels) of oxygen (Miot et al.,
2009). Microorganisms are diverse and the role they play in Vivianite formation is
critical but there is still limited understanding of the important role they play in the
archaeological environment (Kip and Van Veen 2015). The microbial flora within with
archaeological deposits at Vindolanda will be extremely complex and will be the
subject of further investigation. It is most likely that there are metal reducing species
as well as iron oxidising species (Schädler 2009) as evidenced by the red brown
deposits appearing in the springs on the site. On bones it is assumed that Vivianite
formation is partly due to the proteins and amino acids acting as iron binding sites
(Johanson 1975). Therefore, mechanisms of formation extend beyond reactions with
hydroxyapatite but also include iron and phosphate (Mann., et al., 1998).
Furthermore, due to the fact that certain microbes can deposit a layer of protective
material on artefacts, these potentially have enormous biotechnological capabilities
(Kip and Van Veen 2015).
Vivianite is known to form in clay deposits and this is likely to be due at least in part
to the ability of clay minerals to bind both cations and anions. It has also been
suggested that clays may act as catalytic sites for the redox reactions of iron and
thus the formation of phosphate materials (Stuki 2011). The post depositional
environment itself should not be underestimated, the remarkable preservation at
Hungate was assumed in part due to the high concentration of tannates present in
the soil (Farrer., et al., 1953). Tannins and humic materials would be expected to be
found within occupation layers due to the great extent of leather working and also
due to the habit of using bracken as well as straw as a floor covering (Birley, 2009).
Tannates can inhibit the activity of bacteria, and includes tannic acid which is found
in oak bark, traditionally used as a mordant in the tannery process (Ford et al.,
2015 ). However, there have been suggestions that tannates may suppress some
bacterial types (sulphate reducing) whilst encouraging others (DMRBs) (Farrer et al.,
1953). There was an intensive culture of leather working at Vindolanda (Birley
2009), supported by the leather finds as well as written on two of the writing tablets
detailing the supply of goats and/or goats skins. Clearly, the Roman army required a
large quantity of leather goods, but many questions remain in respect to the kind of
Page 13 of 17
leather, number of hides, processing technology, species and extent of leather trade
across the Roman empire (Groenman-van Waateringe., 2009). Let alone whether
the leather used was produced at or very near to Vindolanda or simply brought in
from further afield.
Complex factors impact on the preservation of archaeological artefacts and these
are not fully understood in the waterlogged environment (Matthiesen et al., 2003;
McGowan and Prangnell 2006). It is clear that Vivianite formation can occur in a
shorter period of time (Cox and Bell., 1999). The preservation of artefacts such as
leather and iron in collections is of paramount importance, thus understanding the
preservation ability of Vivianite would greatly aid (Wang 2007; Zangarini et al., 2016).
Vivianite has been seen on a diverse range of archaeological artefacts and has now
been confirmed as the blue substance at Vindolanda. Further work is needed to
answer fundamental issues such as what are the balances of materials, chemicals
and biological agents in the soil surrounding the formation of Vivianite and how do
these help us understand the processes of archaeological preservation.
Conclusion
This is the first study that characterises Vivianite from a Roman site in the UK.
Extensive chemical consideration of the blue substance has been undertaken
leading to the more confident identification of the blue substance being Vivianite.
This will aid further investigations of chemical and microbiological processes within
the depositional environment. Unravelling these processes will aid understanding of
preservation processes and thus management of important sites of national and
international significance such as Vindolanda.
Acknowledgements
We thank the Vindolanda Trust who granted us permission to take samples for ana-
lysis. Thank you to Dr Chris Pask and Ms Lesley Neve, University of Leeds who un-
dertook the XRD experimentation and analysis.
Page 14 of 17
References
Birley, R. (2009) Vindolanda: A Roman frontier fort on Hadrian’s Wall. Gloucestershire: Amberley Publishing.
Booth, G.H., Tiller, A.K., Wormwell, F. (1962) A laboratory study of well-preserved ancient iron nails from apparently corrosive soils. Corrosion Science. 2 (3) pp. 197-202
Cox, M., Bell, L. (1999) Recovery of human skeletal elements from a recent UK murder Inquiry: Preservational signatures. Journal of Forensic Science. 44 (5) pp. 945-950
Egger, M., Jilbert, T., Behrends, T., Rivard, C., Slomp, C.P (2015) Vivianite is a major sink for phosphorus in methanogenic coastal surface sediments. Geochimica et Cosmochimica Acta 169 pp. 217-235
Farrer, T.W., Biek, L., Wormwell, F. (1953) The role of tannates and phosphates in the preservation of ancient buried iron objects. Journal of Applied Chemistry. 3 pp. 80-83
Ford, L., Rayner, C.M. Blackburn, R.S. (2015). Isolation and extraction of ruberythric acid from Rubia tinctorum L. and crystal structure elucidation. Phytochemistry. 117 pp.168-173
Frost, R.L., Martens, W., Williams, P.A., Kloprogge, J.T. (2002). Raman and infrared spectroscopic study of the vivianite-group phosphates vivianite, baricite and bobierrite. Mineralogical Magazine 66 (6) pp. 1063-1073
Groenman-van Waateringe, W. (2009) The sources of hides and skins for Roman army equipment. In Hanson (Ed) The Army and Frontiers of Rome: 74: pp 209
Johanson, G. (1975) Cannon-Ball iron in teeth and jaws: Odontological identification of findings from the warship Wasa 1628. Forensic Science 5 (2) pp. 139-140
Kip, N., Van Veen J.A. (2015). The dual role of microbes in corrosion. ISME Journal. 9 (3) pp. 542-551
Kloprogge, J.T., Visser, D., Martens, W.N., Duong, L.V., Frost, R.L. (2003) Identification by raman microscopy of magnesian Vivianite formed from Fe, Mg, Mn and PO4 leached from metal and bone fragments in a Roman camp near Fort Vechten, Utrecht, the Netherlands. Netherlands Journal of Geosciences. 82 (2) pp. 209-214
Page 15 of 17
Li, Q., Wang, X., Kan, D., Barlett, R., Pinay, G., Ding, Y.S., Ma, W. (2012). Enrichment of phosphate on ferrous iron phases during bio-reduction of ferrihydrite. International Journal of Geosciences 3 pp. 314-320
Mann, R.W., Feather, M.E., Tumosa, C.S. Holland, T.D., Schneider, K.N. (1998) A blue encrustation found on skeletal remains of Americans missing in action in Vietnam. Forensic Science International. 97 (2-3) pp. 79-86
Maritan, L. Mazzoli, C. (2004) Phosphates in archaeological finds: Implications for environmental conditions of burial. Archaeometry. 46 (4) pp. 673-683
Matthiesen, H., Hilbert, L.R. Gregory, D.J. (2003) Siderite as a corrosion product on archaeological iron from a waterlogged environment. Studies in Corrosion. 48 (3) pp 183-194
McGowan, G., Prangnell, J. (2006) The significance of Vivianite in archaeological settings. Geoarchaeology. 21 (1) pp 93-111
Melton, E.D., Swanner, E.D., Behrens, S., Schmidt, C., Kappler, A. (2014) The interplay of microbially mediated and abiotic reactions in the biogeochemical Fe cycle. Nature Reviews: Microbiology. 12 (12) pp. 797- 808
Miot, J., Benzerara, K., Morin, G., Bernard, S., Beyssac. O., Larquet, E., Kappler, A., Guyot, F. (2009) Transformation of vivianite by anaerobic nitrate-reducing iron-oxidizing bacteria. Geobiology. 7 (3) pp. 373-384
Nanzyo, M., Yaginuma, H., Sasaki. K., Ito, K., Aikawa, Y., Kanno, H., Takahashi, T. (2010) Identification of Vivianite formed on the roots of paddy rice grown in pots. Soil Science and Plant Nutrition. 56 (3) pp. 376-381
O'Connell, D. W., Jensen, M.M. Jakobsen, R., Thamdrup, B., Anderson, T.J. Kovacs, A., Hansen, H.C.B. (2015) Vivianite formation and its role in phosphorus retention in Lake Ørn, Denmark. Chemical Geology. 409 pp. 42-53
Read, H.H. (1970) Rutley’s Elements of Mineralogy. Twenty-Sixth Edition. George Allen & Unwin Ltd
Rodgers, K.A. (1986) Metavivianite and kerchenite: A review. Mineralogical Magazine. 50 (4) pp. 687-691
Rothe, M., Frederichs, T., Eder, M., Kleeberg, A. Hupfer, M. (2014) Evidence for vivianite formation and its contribution to long-term phosphorus retention in a recent lake sediment: A novel analytical approach. Biogeosciences. 11(18) pp. 5169-5180
Rothe, M., Kleeberg, A., Hupfer, M. (2016) The occurrence, identification and environmental relevance of vivianite in waterlogged soils and aquatic sediments. Earth-Science Reviews. 158 pp. 51-64
Sameshima, T., Henderson, G.S., Black, P.M., Rodgers, K.A. (1985). X-ray diffraction studies of vivianite, metavivianite, and baricite. Mineralogical Magazine. 49(1) pp. 81-85
Page 16 of 17
Schädler, S., Burkhardt, C., Hegler, F., Straub, K.L., Miot, J., Benzerara K., Kapler, A. (2009) Formation of cell-iron mineral aggregates by phototrophic and nitrate-reducing anaerobic Fe(II)-oxidizing bacteria. Geomicrobiology Journal. 26 (2) pp. 93-103
Stuki J W. (2011) A review of the effects of iron redox cycles on smectite properties. Comptes Rendus Geoscience. 343 (2-3) pp. 199-209
Walpersdorf, E., Koch, C.B., Heiberg, L., O’Connell, D.W., Kjaergaard, C., Hansen, H.C.B. (2013) Does Vivianite control phosphate solubility in anoxic meadow soils. Geoderma. 193-194 pp. 189-199
Wang, Q. (2007) An investigation of deterioration of archaeological iron. Studies in Conservation. 52 (2) pp. 125-134
Zangarini, S., Trombino, L., Cattaneo, C. (2016) Micromorphological and ultramicroscopic aspects of buried remains: Time-dependent markers of decomposition and permanence in soil in experimental burial. Forensic Science International. 263 pp. 74-82
Page 17 of 17