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Reply to Wierzchos et al.: Microorganism-induced gypsum to anhydrite phase transformation
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In response to Wierzchos et al. (1) regarding the mechanism of water extraction from gypsum rock by desert colonizing microorganisms (2), we provide details that refute their incorrect assessments.
We carefully selected areas without microorganism colonies that only contained gypsum, as confirmed by X-ray diffraction (XRD), for our culture experiments. Raman is useful for localized analysis of phase on surfaces, but here, it is complementary to XRD, which provides sample-wide detection (3, 4). Furthermore, selected area electron diffraction (SAED) confirms anhydrite, exhibiting arcs at 0.347 ± 0.003 nm and 0.278 ± 0.002 nm [(200) and (211) planes, respectively] with a [01−1] zone axis (Fig. 1 A and B). The closest reflection for gypsum, the (130) plane, was not observed. SAED and fast Fourier transform (FFT) show twofold symmetry of the arcs, while the gypsum (130) plane exhibits fourfold symmetry, which was not observed. Finally, the crystal morphology of gypsum (monoclinic) was observably different from anhydrite (orthorhombic) (Fig. 1 C−F). Thus, XRD, high-resolution …
↵1To whom correspondence may be addressed. Email: david.k{at}uci.edu.
References
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- J. Wierzchos et al.
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- W. Huang et al.
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- N. Prieto-Taboada et al.
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- A. L. Ulery,
- L. Richard Drees
- W. Harris,
- G. N. White,
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- ↵
- L. A. Hardie
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- ↵
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- J. Schmitt,
- H.-C. Flemming
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