Pentahydrite Structure
Pentahydrite MgSO4*5(H2O) earns an "honorable mention" as a musheral because it doesn't quite have as many water molecules as other atoms. It has six atoms in its formula versus five water molecules. Nonetheless it's pretty watery. It is very nearly isostructural with Chalcanthite, CuSO4*5(H2O), differing only slightly in lattice dimensions.
Pentahydrite is triclinic. This view looks down the a axis at the b-c plane. The structure consists of octahedra (blue) surrounding the magnesium atoms. The octahedra share oxygens at either end with sulfate tetrahedra (yellow). The other four vertices are water molecules. There are also two independent water molecules in each unit cell, with their oxygens shown in blue. The octahedra and sulfate tetrahedra form zigzag chains that also undulate above and below the plane of the diagram.
This view looks down the b axis, with the c axis across the diagram and the a axis nearly vertical. Although the chains look continuous, that's merely a perspective effect due to overlap. In each unit cell, the chains extend from left front to right rear. The left and middle octahedra are joined, but the right rear octahedron is concealed by a new chain entering the picture.
This view looks along the b axis. Again, although the chains look continuous, that's merely a perspective effect due to overlap. In each unit cell, the chains extend from left front to right rear.
Steven Dutch, Professor Emeritus, Natural and Applied Sciences, Universityof Wisconsin - Green Bay
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Created 15 October 2009, Last Update