Polylithionite - KLi₂AlSi₄O₁₀F₂

Polylithionite is a phyllosilicate mineral, member of the Mica group. The name was introduced by Lorenzen (1884) and comes from the Greek "Poly" for "many or much" and Lithium, in allusion to its composition with a high Lithium. It was fist discovered in a lithium-rich syenite pegmatites at Kangerdluarssuk in Greenland. Polylithionite, like other micas, has a layered structure of lithium aluminum silicate sheets weakly bonded together by layers of potassium ions. These potassium ion layers produce the perfect cleavage. Polylithionite is a common mineral in irregular segregation and veinlets, as late stage and metasomatic replacement mineral, in syenite pegmatites and in alkalic or agpaitic rocks (Lovozero, Ilìmaussaq, Mont Saint-Hilaire etc).

Optical Properties:
• Form: Occurs as tabular-micaceous crystals, also scaly, fine grained.
• Relief: Low.
• Color: Colorless.
• Pleochroism: None to weak.
• Cleavage: (001) perfect.
• Interference colors: Medium-low (from gray to yellow-orange).

polylithionite micaceous crystals from Mont Saint-Hilaire, Quebec, Canada. image from RRUFF

Bibliography

• Cox et al. (1979): The Interpretation of Igneous Rocks, George Allen and Unwin, London.
• Howie, R. A., Zussman, J., & Deer, W. (1992). An introduction to the rock-forming minerals (p. 696). Longman.
• Le Maitre, R. W., Streckeisen, A., Zanettin, B., Le Bas, M. J., Bonin, B., Bateman, P., & Lameyre, J. (2002). Igneous rocks. A classification and glossary of terms, 2. Cambridge University Press.
• Middlemost, E. A. (1986). Magmas and magmatic rocks: an introduction to igneous petrology.
• 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.

Photo
Polylithionite crystals (colorless) in a agpaitic syenite. Ilimaussaq complex, Greenland. PPL image, 10x (Field of view = 2mm)	Polylithionite crystals (yellow-orange) and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. XPL image, 10x (Field of view = 2mm)	Polylithionite crystals (colorless), eudyalite (high relief) and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. PPL image, 10x (Field of view = 2mm)
Polylithionite crystals (yellow), eudyalite (gray) and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. XPL image, 10x (Field of view = 2mm)	Polylithionite crystals (colorless), aegirine (green) and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. PPL image, 10x (Field of view = 2mm)	Polylithionite crystals (yellow), aegirine and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. XPL image, 10x (Field of view = 2mm)
Polylithionite crystals (gray), aegirine and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. XPL image, 20x (Field of view = 1mm)	Polylithionite crystals (colorless), aegirine (green) and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. PPL image, 20x (Field of view = 1mm)	Polylithionite crystals (yellow), aegirine and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. XPL image, 20x (Field of view = 1mm)
Polylithionite crystals (yellow), aegirine and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. XPL image, 20x (Field of view = 1mm)	Polylithionite crystals (colorless), aegirine (green) and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. PPL image, 20x (Field of view = 1mm)	Polylithionite crystals (yellow), aegirine and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. XPL image, 20x (Field of view = 1mm)
Polylithionite crystals (yellow-orange), aegirine and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. XPL image, 20x (Field of view = 1mm)	Polylithionite crystals (colorless), aegirine (green) and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. PPL image, 20x (Field of view = 1mm)	Polylithionite crystals (yellow-orange), aegirine and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. XPL image, 20x (Field of view = 1mm)
Polylithionite crystals (yellow), aegirine and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. XPL image, 20x (Field of view = 1mm)	Polylithionite crystals (yellow), aegirine and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. XPL image, 20x (Field of view = 1mm)	Polylithionite crystals (yellow), aegirine and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. XPL image, 20x (Field of view = 1mm)
Polylithionite crystals (colorless), eudyalite (high relief) and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. PPL image, 20x (Field of view = 1mm)	Polylithionite crystals (yellow), eudyalite (gray) and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. XPL image, 20x (Field of view = 1mm)	Polylithionite crystals (yellow), eudyalite (gray) and feldspar in a agpaitic syenite. Ilimaussaq complex, Greenland. XPL image, 20x (Field of view = 1mm)

Fundamental Minerals

Sialic Minerals

Femic Minerals

Accessory Minerals

Rare Accessory

Alteration Products

Microstructures

Rocks

Polylithionite - KLi2AlSi4O10F2

Polylithionite - KLi₂AlSi₄O₁₀F₂