Article
Article
Lawsonite
Article By:
Moore, Paul B. Department of the Geophysical Sciences, University of Chicago, Chicago, Illinois.
Last reviewed:November 2019
DOI:https://doi.org/10.1036/1097-8542.374000
A metamorphic silicate mineral related chemically and structurally to the epidote group of minerals. Its composition is Ca(H2O)Al2(OH)2[Si2O7], and it is a sorosilicate based on the dimeric [Si2O7]6− radical, where two (SiO4) tetrahedra link at a common vertex to form a bow-tie arrangement. The water molecule is bonded directly to the calcium ion and is tightly held. Although the calcium (Ca2+) and the aluminum (Al3+) cations are octahedrally coordinated by anions (and the water molecule), and the silicon cation (Si4+) is tetrahedrally coordinated by the anions, the structure is not limitingly closest-packed.
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