Geology Reference
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Fig. 23. (a) Intercrystalline porosity between sparry crystals, thin laminae are visible within the crystals (arrows), tufa
formed on limestone tablet at Karw´ w cascade point between June and October 2003; (b) sparry crystals developed
directly on copper tablet exposed between August 2002 and October 2003, note the high intercrystalline porosity and
small pits in the crystals being traces of cyanobacteria or diatom stalks, sparite is capped by micrite, H´j dam point
(c) compact sparry lamina formed directly on copper tablet, the smooth surface is the basement of sample visible due
to detaching of the tablet, tufa formed at Karw´ w cascade point between June and October 2003; (d) sparry crystals
developed on both sides of a leaf incorporated into tufa formed on limestone tablet at L´ ˇky E point between June and
October 2003, compare Figure 9b; a, d - thin sections, b, c - SEM images.
streams in Belgium by Janssen et al. (1999) and
in Germany by Merz-Preiß & Riding (1999). Folk
(1994) found travertine in a Tuscany spring
growing considerably slower on copper than on
other substrates. All these facts were ascribed to
the toxicity of copper towards algae, and this view
is accepted herein.
The fact that the weight of tufa deposited on
limestone tablets was substantially and persistently
higher than on copper tablets exposed in the same
conditions for the same time supports the idea that
copper inhibits tufa growth (Figs 7 & 8; Table 3).
The difference in growth rates was always sig-
nificant when tufa deposited on a limestone tablet
contained biogenic components. In extreme case
copper tablets were not covered by tufa at all. This
suggests that micro-organisms inhabiting the lime-
stone tablets promote faster and more efficient
tufa growth.
Other causes that can affect the difference
between the rate of tufa growth on copper and lime-
stone tablets are rate of nucleation and toxicity of
copper ions in solution. Copper basement can be
quickly overgrown by calcite, which has been
proved in a series of experiments carried out by
Chibowski et al. (2003). Nonetheless, in the same
chemical conditions, calcite is prone to nucleate
quicker on limestone than on copper because of
structural similarity between the nucleating phase
and its substratum (see Bathurst 1976, 437). The
difference in the weight of tufa formed on paired
limestone and copper tablets may be used for esti-
mation of this process only when tufa covering
both tablets displays crystalline fabrics without sub-
stantial traces of algae, that is when any significant
influence of algae on tufa growth can be ruled out.
This is the case at the L ´ˇky E site. Tufa growing
there on both tablets constituting a pair between
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