Dehydration (mineralogy)
Dehydration reactions (dehydration reactions) are reactions in which the water of crystallization bound in minerals is released when the temperature rises . Almost all reactions during rock metamorphosis belong to this group. Water in minerals is usually the pressure-transmitting medium, and the water pressure therefore corresponds to the total pressure of the entire system P H 2 O = P total .
A typical dehydration reaction in mineralogy is, for example, that of the clay mineral kaolinite , which disintegrates into pyrophyllite and water in the presence of quartz when metamorphosis begins :
- Al 4 [(OH) 8 | Si 4 O 10 ] + 4 SiO 2 → 2 Al 2 [(OH) 2 | Si 4 O 10 ] + H 2 O
As the temperature continues to rise, pyrophyllite changes into andalusite or kyanite ( thistle ), quartz and water:
- Al 2 [(OH) 2 | Si 4 O 10 ] → Al 2 [O | SiO 4 ] + 3 SiO 2 + H 2 O
Other dehydration reactions include the disintegration of antigorite to forsterite and talc and of muscovite to quartz.
literature
- Martin Okrusch, Siegfried Matthes: Mineralogy. An introduction to special mineralogy, petrology and geology . 7th, completely revised and updated edition. Springer, Berlin [a. a.] 2005, ISBN 3-540-23812-3 , pp. 363-364 .