Crystal Structure
Though lawsonite and anorthite have similar compositions, their structures are quite different. While anorthite has a tetrahedral coordination with Al (Al substitutes for Si in feldspars), lawsonite has an octahedral coordination with Al, making it an orthorhombic sorosilicate with a space group of Cmcm which consists of Si2O7 Groups and O, OH, F, and H2O with cations in and/or > coordination. This is much similar to the epidote group which lawsonite is often found in conjunction with, which are also sorosilicates because their structure consists of two connected SiO4 tetrahedra plus connecting cation. The water contained in its structure is made possible by cavities formed by rings of two Al octahedral and two Si2O7 groups, each containing an isolated water molecule and calcium atom. The hydroxyl units are bound to the edge-sharing Al octahedral (Baur, 1978).
Read more about this topic: Lawsonite
Famous quotes containing the words crystal and/or structure:
“Come live with me, and be my love,
And we will some new pleasures prove
Of golden sands, and crystal brooks,
With silken lines, and silver hooks.”
—John Donne (1572–1631)
“Communism is a proposition to structure the world more reasonably, a proposition for changing the world. As such, we have to analyze it and, if we deem it reasonable, act upon it.”
—Friedrich Dürrenmatt (1921–1990)