Antigorite periodicity
Serpentine minerals categorization based on ratio
The brucite–lizardite–talc line:
Antigorite
Serpentine formula /
The periodicity is related to cell size and is also an “indicator” for the depletion of against lizardite.
Antigorite is not a serpentine polymorph strictu sensu, because of the discrete depletion (Capitani & Mellini, 2004)
The values of antigorite commonly range from 23 to 14 in natural metamorphic serpentinites. (Shen et al., 2020)
When (no depletion), we get lizardite .
The depletion formula
valve vs.
Low values are more stable at high temperature (Kunze 1961; Trommsdorff 1983; Mellini et al. 1987; Uehara and Kamata 1994). (Shen et al., 2020)
Wunder et al. (2001) performed an experimental study at 350–710 °C, 2–50 kbar in the simple MSH system and found that the a-axis (related to the value) is roughly negatively correlated with temperature but positively correlated with pressure. (Shen et al., 2020)
Number of atoms =
| Periodicity () | Formula () | # atoms () |
|---|---|---|
| 13 | 219 | |
| 17 | 291 | |
| 23 | 399 |
References
- Capitani, G., & Mellini, M. (2004). The modulated crystal structure of antigorite: The m = 17 polysome. American Mineralogist, 89(1), 147–158. https://doi.org/10.2138/am-2004-0117
- Mellini, M., & Zanazzi, P. F. (1987). Crystal structures of lizardite-1T and lizardite-2H1 from Coli, Italy. American Mineralogist, 72(9–10), 943–948.
- Mellini, M., Trommsdorff, V., & Compagnoni, R. (1987). Antigorite polysomatism: Behaviour during progressive metamorphism. Contributions to Mineralogy and Petrology, 97(2), 147–155. https://doi.org/10.1007/BF00371235
- Shen, T., Zhang, C., Chen, J., Hermann, J., Zhang, L., Padrón-Navarta, J. A., Chen, L., Xu, J., & Yang, J. (2020). Changes in the cell parameters of antigorite close to its dehydration reaction at subduction zone conditions. American Mineralogist, 105(4), 569–582. https://doi.org/10.2138/am-2020-7159