Although potentially stable at lower pressure and low temperature, the activity of water is usually high enough under such conditions that it is replaced by hydrous aluminosilicates such as muscovite, pyrophyllite, or kaolinite.
12.
Another example are the aluminosilicates kyanite, andalusite, and sillimanite ( polymorphs, as they share the formula Al 2 SiO 5 ), which differ by the coordination number of the Al 3 +; these minerals transition from one another as a response to changes in pressure and temperature.
