Lawsonite - CaAl2Si2O7(OH)2*(H2O)

Named in 1895 in honor of geologist Andrew Cowper Lawson, geologist with the Canadian Geological Survey and for most of his career a professor of geology and mineralogy at the University of California. The structure of Lawsonite contains chains of edge-sharing Al(O,OH)6 octahedra parallel to c axis. The chains are united laterally by Si2O7 double tetrahedron units that share corners with chains octahedra. Calcium ions and H2O molecules fill independent voids in the structure and satisfy electrostatic neutrality. Lawsonite is a metamorphic mineral typical of the blueschist facies. It also occurs as a secondary mineral in altered gabbro and diorite. Associate minerals include epidote, titanite, glaucophane, garnet and quartz.

Optical properties:

Form: Usually occurs as euhedral crystals and usually tabular.
• Color: Colourless
• Relief: Moderate
• Interference colors: Low, first order yellow and white.


Bibliography



• Bucher, K., & Grapes, R. (2011). Petrogenesis of metamorphic rocks. Springer Science & Business Media.
• Fossen, H. (2016). Structural geology. Cambridge University Press.
• Howie, R. A., Zussman, J., & Deer, W. (1992). An introduction to the rock-forming minerals (p. 696). Longman.
• Passchier, Cees W., Trouw, Rudolph A. J: Microtectonics (2005).
• Philpotts, A., & Ague, J. (2009). Principles of igneous and metamorphic petrology. Cambridge University Press.
• Shelley, D. (1993). Igneous and metamorphic rocks under the microscope: classification, textures, microstructures and mineral preferred-orientations.
• Vernon, R. H. & Clarke, G. L. (2008): Principles of Metamorphic Petrology. Cambridge University Press.
• Vernon, R. H. (2018). A practical guide to rock microstructure. Cambridge university press.


Photo
glaucofanemilos(21).jpg

Rectangular, colorless lowsonite crystals. Milos (Greece). PPL image, 10x (Field of view = 2mm)
glaucofanemilos(26).jpg

Rectangular, colorless lowsonite crystals. Milos (Greece). PPL image, 10x (Field of view = 2mm)
glaucofanemilos(27).jpg

Rectangular lowsonite crystals. Milos (Greece). XPL image, 10x (Field of view = 2mm)
glaucofanemilos(28).jpg

Rectangular lowsonite crystals. Milos (Greece). XPL image, 10x (Field of view = 2mm)
glaucofanemilos(31).jpg

Rectangular lowsonite crystals. Milos (Greece). XPL image, 10x (Field of view = 2mm)
glaucofanemilos(32).jpg

Rectangular, colorless lowsonite crystals. Milos (Greece). PPL image, 10x (Field of view = 2mm)
glaucofanemilos(33).jpg

Rectangular lowsonite crystals. Milos (Greece). XPL image, 10x (Field of view = 2mm)
glaucofanemilos(34).jpg

Rectangular, colorless lowsonite crystals. Milos (Greece). PPL image, 10x (Field of view = 2mm)
glaucofanemilos(35).jpg

Rectangular lowsonite crystals. Milos (Greece). XPL image, 10x (Field of view = 2mm)
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Rectangular, colorless lowsonite crystals in a blueschist. PPL image, 10x (Field of view = 2mm)
lawsonite11(3).jpg

Rectangular lowsonite crystals in a blueschist. XPL image, 10x (Field of view = 2mm)
lawsonite11(4).jpg

Rectangular lowsonite crystals in a blueschist. XPL image, 10x (Field of view = 2mm)