Kalsilite - KAlSiO₄

Kalsilite (pure potash analogue to nepheline) is a very rare mineral occurring in volcanic rocks very poor in Si and Na. It appear in groundmass grains or phenocrysts, sometime complexly zoned ore intergrowth with nepheline. Kalsilite may contain minor Na and may be unusually rich in Ferric iron, which replace Al. Kalsilite is a common Mineral in some rare rocks such as venanzites (a rare kamafugitic rock, a kalsilite-phlogopite-olivine-leucite melilitite).

Optical properties
• Color:colorless.
• Form: Tabular crystals or granula aggregates.
• Interference colors: I order white-gray.
• Relief: low.

White acicular crystals of kalsilite in a venanzite. San Venanzo, Italy. From RRUFF

White acicular single crystals of kalsilite, associated with thinner colorless fluorapatite and brown tabular phlogopite. San Venanzo, Italy. 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
kalsilite crystal in a venanzite. PPL image , 10x (Field of view = 2mm)	kalsilite crystal in a venanzite. XPL image , 10x (Field of view = 2mm)	kalsilite crystal in a venanzite. XPL image , 10x (Field of view = 2mm)
Basal section of kalsilite in a venanzite. XPL image , 10x (Field of view = 2mm)	kalsilite crystal in a venanzite. XPL image , 10x (Field of view = 2mm)	kalsilite crystal in a venanzite. XPL image , 10x (Field of view = 2mm)
kalsilite crystal in a venanzite. XPL image , 10x (Field of view = 2mm)	kalsilite crystal in a venanzite. XPL image , 10x (Field of view = 2mm)	kalsilite crystal in a venanzite. XPL image , 10x (Field of view = 2mm)
Melilite, Phlogopite and Kalsilite (gray). XPL image , 10x (Field of view = 2mm)	kalsilite crystal in a venanzite. XPL image , 10x (Field of view = 2mm)	Melilite, Phlogopite and Kalsilite (gray). XPL image , 10x (Field of view = 2mm)