Supporting Online Material
Materials and methods
Barium chloride stock solution was prepared at 10 mM in water with BaCl2.2H2O
crystalline powder purchased from Probus. Sodium silicate (ca. 27% SiO2, 14% NaOH,
density 1.390 g/cm3) was obtained from Sigma-Aldrich. Formaldehyde solution, sodium
hydroxide flakes, ethanoic acid and phenol were obtained from BDH Chemicals, Asia
Pacific Specialty Chemicals Limited and Ajax Chemicals Ltd respectively. The silicawitherite biomorphs were prepared by mixing 10 mM stock barium chloride with sodium
silicate solution (diluted with water 1:500) in a 1:1 (v/v) ratio. The final mixture had a pH
of ca. 10.5 with at most minor adjustment using 0.1 M NaOH. The diluted solution was
aliquotted in 2 ml volumes into each well of 24-well Linbro culture plates purchased from
Hampton Research, Laguna Niguel, CA. All syntheses occurred under loose covers, to
prevent dust contamination but allow equilibration with atmospheric CO2, thus ensuring the
formation of HCO3 - and CO32- in the range of the working pH. Vesicular aggregates were
observed within two hours, but growth was allowed to continue for up to 48 hours before
harvesting.
Time-lapse optical micrographs showing the morphological development during growth are
shown in Movies S1-S3.
Witherite-silica aggregates were harvested from the solution with a soft paintbrush, washed
in distilled water and ethanol, and then dried at room temperature. FESEM and analytical
SEM samples were mounted on stubs with double-sided carbon tape and dried further
overnight at ca. 60oC, prior to being platinum-coated for examination in the microscope.
TEM samples were floated onto Cu/holey carbon grids. The microscopes used were located
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at the ANU Electron Microscopy Unit and were a Hitachi S4500 (FESEM) and a JEOL
JSM6400 SEM and Philips EM 430 TEM, both fitted with Oxford ISIS EDXA systems.
X-ray diffraction patterns were collected on CCD from sheet and helical aggregates in a
Nonius Kappa four-circle diffractometer (Research School of Chemistry, Aust. Natl.
Univ.).
The adsorption and condensation of organics were conducted in a 15 ml Teflon-coated
stainless steel bomb, containing 10 ml of the organic mixture, 0.01 M phenol solution and
0.02 M formaldehyde solution, together with previously prepared biomorphs. The vessel
was then sealed, and heated at 125 °C for a minimum of 15 hours. The resulting products,
distinctly brown in colour compared with the pure inorganic biomorphs, were subsequently
rinsed with distilled water. These products were first aged at 160 °C for 45 hours in air and
then transferred to a Lindberg tube furnace, model 54433 equipped with an 818 temperature
controller and carbonised in a nitrogen flow of 1650 ml/min. All samples were treated in
500°C for a minimum of 5 hours with a heating rate of 1°C/min from 200 °C to 500 °C.
Selected samples were analysed with a Renishaw Raman imaging microscope, model 2000,
equipped with Helium/Neon (632.8 nm) and low power near infrared (780 nm) lasers and a
low noise (thermoelectrically cooled to -70 °C) CCD. The spatial resolution of the spectra
(collected with a 100x objective lens) is approximately 1 µm, with a depth of field of 2 µm.
The aggregates were imaged using optical microscopy and FESEM (accelerating potential
usually 5 kV, working distance 5-9 mm).
X-ray diffraction was used to identify crystalline phases and their orientations;
specimens were also characterised by electron diffraction, Fourier transform infrared and
Raman spectroscopy, and energy-dispersive X-ray analysis (EDXA). The silicate and
carbonate phases in some specimens were selectively removed by alkaline or acid
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dissolution, using 0.01M NaOH and 0.01M ethanoic solutions respectively. A time-lapse
sequence of optical micrographs showing witherite dissolution is shown in Movie S4.
EDXA analyses of biomorphs all showed low totals due to the hydrated, porous and nonplanar nature of the samples. Nevertheless, elemental analyses were found to behave in a
consistent fashion. Specimens were analyzed for Na, Si, Cl and Ba using as standards
albite, sanidine, sylvite and barite respectively. Accelerating potential was 15kV and beam
current 1nA. Strong C and O Kα peaks were observed but quantification was unreliable for
these elements. Near-total removal of Ba by leaching with dilute HCl implied that virtually
all Ba was present as carbonate, so a weight percentage of CO2 was calculated on that basis.
The analyses were then apportioned into wt% of NaCl (present due to incomplete washing),
BaCO3 and an anhydrous equivalent of the silicate phase Na2xSiO2+2x. These percentages,
the Na:Si ratio of the silicate phase x, and the mass ratio of carbonate to dry silicate
(C/C+S) are shown in Table S1 for 3-4 examples of different biomorph morphologies with
both silicate and carbonate phases present (washed in water + ethanol only) and also after
leaching in HCl to remove carbonate (one example of each morphology). It is apparent that
there is no significant difference between composition ranges for the different
morphologies. The anhydrous mass of the untreated samples is 26-42% witherite, the
remainder being a sodium silicate with Na:Si in the range 0.07-0.15 and negligible Ba
content. Acid leaching removes all of the carbonate phase and the Na from the silicate,
leaving only amorphous hydrated silica. The structurally bound H2O content remains to be
determined directly.
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Figure S1: Field emission scanning electron micrograph (FESEM) showing cluster of rodshaped silica-witherite colloids within an ethanol- water-rinsed biomorph (gel or sol).
Figure S2: FESEM showing individual pseudo-hexagonal silica-witherite colloids.
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Figure S3: Transmission electron micrograph of an alkaline-washed biomorph, showing
individual pseudo-hexagonal witherite crystallites.
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Movie S1: Animated sequence of time-lapse optical micrographs showing development of
silica-witherite biomorph sheets and formation of rope-like helical filaments from cusps on
the sheet perimeter.
Movie S2: Animated sequence of time-lapse optical micrographs showing growth of helical
filaments (later growth of sample shown in Movie S1)
Movie S3: Animated sequence of time-lapse optical micrographs showing growth of “fat”
helical filaments.
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Movie S4: Animated sequence of time-lapse optical micrographs showing dissolution of
witherite material by immersion of biomorph in .1M acetic acid (sequence recorded over a
few hours). Note the retention of the (relatively transparent) silica skin.
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wt%
sheets (4)
helices (3)
spherical (3)
HCl-treated (3)
Na2O
SiO2
1.75-2.95
26.42-38.89
1.81-2.44
26.70-30.54
1.98-2.83
29.26-34.76
0.04-0.32
59.08-69.80
Cl2O-1
0.13-1.18
0.09-0.45
0.43-0.57
0.18-0.28
BaO
10.90-18.05
12.96-18.14
12.75-13.47
0.22-0.29
CO2 (calc)
3.12-5.18
3.72-5.21
3.66-3.86
0.06-0.08
Total
50.96-57.55
49.10-57.71
49.65-54.52
59.73-70.66
NaCl
0.28-2.51
0.20-1.02
0.92-1.20
0.38-0.59
BaCO3
14.02-23.24
16.68-23.35
16.41-17.33
0.29-0.37
Na2xSiO2+x
28.40-40.70
28.45-36.59
31.62-36.37
58.98-69.98
x
0.07-0.13
0.10-0.13
0.08-0.15
0
C/(C+S)
0.26-0.42
0.31-0.42
0.32-0.35
0.004-0.006
250µm
Table S1. EDXA analyses of biomorphs.
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