Fundamental Minerals

Sialic Minerals

Feldspars

Feldspathoids

Quartz

Femic Minerals

Spodumene

Accessory Minerals

Rare Accessory

Alteration Products

Microstructures

Rocks

Jacupiranga complex

Leucite - KAlSi₂O₆

Leucite is usually included as a feldspathoid by petrologists, as it is a common primary rock-forming mineral in some high-potassium rocks but, despite being anhydrous, structurally it also has a topological relation to zeolites, especially analcime, and thus is typically included in that family also.

The name leucite derives From greek leucos meaning "white"; Leucite structure is similar to that of analcime and pollucite, and it is based on a cubic lattice containing rings of four and six tetrahedra oriented normal to the fourfold and threefold symmetry axis. The leucite structure is characterized by two distinct sites, available for large cations; the larger sites contain K⁺ ions and the smaller sites are vacant, yielding a very open, low-density structure.
Leucite is common in some volcanic rocks in which it crystallises with a cubic crystal structure at high temperature (ca. 900°C), forming isometric trapezohedral crystals. Upon cooling to 700-600°C, it transforms into a tetragonal modification which is stable at room temperature, and forms characteristic polysynthetic twin lamellae. The transformation is reversible. Leucite in confined to volcanic or shallow dike rocks that are Si-poor, Na-poor and K-rich. Lucite occurrences are sufficiently rare to make practical the actual listing of specific localities. Is common in Italy (Vulsini, Vesuvius), in the Lucite hills of Wyoming, and in some areas of Africa.

Optical properties

• Color: Colorless
• Form: Normally forms trapezohedron crystals, with octahedral to roughly circular outline in thin section
• Interference colors: Very low, no more than dark first-order gray
• Relief: Low
• Twinning: Several set of diffuse, parallel twin lamellae resemble those of microcline but tend to appears in three set, intersecting at about 60°.

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.

Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 2x (Field of view = 7mm)	Leucite (clorless) and clinopyroxene crystals in a foidolite with leucite. PPL image, 2x (Field of view = 7mm)	Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 2x (Field of view = 7mm)
Leucite (clorless) and clinopyroxene crystals in a foidolite with leucite. PPL image, 2x (Field of view = 7mm)	Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image. 2x (Field of view = 7mm)	Leucite (clorless) and clinopyroxene crystals in a foidolite with leucite. PPL image, 2x (Field of view = 7mm)
Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image 2x (Field of view = 7mm)	Leucite (clorless) and clinopyroxene crystals. PPL image, 2x (Field of view = 7mm)	Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image. 2x (Field of view = 7mm)
Leucite (clorless) and clinopyroxene crystalsin a foidolite with leucite. PPL image, 2x (Field of view = 7mm)	Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 2x (Field of view = 7mm)	Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 2x (Field of view = 7mm)
Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 10x (Field of view = 2mm)	Leucite (clorless) and clinopyroxene crystals in a foidolite with leucite. PPL image, 10x (Field of view = 2mm)	Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 10x (Field of view = 2mm)
Leucite (clorless) and clinopyroxene crystals in a foidolite with leucite. PPL image, 10x (Field of view = 2mm)	Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 10x (Field of view = 2mm)	Leucite (clorless) and clinopyroxene crystals in a foidolite with leucite. PPL image, 10x (Field of view = 2mm)
Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 10x (Field of view = 2mm)	Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 10x (Field of view = 2mm)	Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 10x (Field of view = 2mm)
Leucite (clorless) and clinopyroxene crystals in a foidolite with leucite. PPL image, 2x (Field of view = 7mm)	Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 10x (Field of view = 2mm)	Leucite (clorless) and clinopyroxene crystals in a foidolite with leucite. PPL image, 2x (Field of view = 7mm)
Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 2x (Field of view = 7mm)	Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 2x (Field of view = 7mm)	Leucite (clorless) and clinopyroxene crystals in a foidolite with leucite. PPL image, 2x (Field of view = 7mm)
Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 2x (Field of view = 7mm)	Leucite (clorless) and clinopyroxene crystals in a foidolite with leucite. PPL image, 2x (Field of view = 7mm)	Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 2x (Field of view = 7mm)
Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 10x (Field of view = 2mm)	Leucite (clorless) and clinopyroxene crystals in a foidolite with leucite. PPL image, 2x (Field of view = 7mm)	Leucite and clinopyroxene crystals in a foidolite with leucite. XPL image, 10x (Field of view = 2mm)
K-feldspar-kalsilite intergrowth. Synnyrite from Synnyr pluton. XPL image, 2x (Field of view = 7mm)	K-feldspar-kalsilite intergrowth. Synnyrite from Synnyr pluton. XPL image, 2x (Field of view = 7mm)	K-feldspar-kalsilite intergrowth. Synnyrite from Synnyr pluton. XPL image, 2x (Field of view = 7mm)
K-feldspar-kalsilite intergrowth. Synnyrite from Synnyr pluton. XPL image, 2x (Field of view = 7mm)	K-feldspar-kalsilite intergrowth. Synnyrite from Synnyr pluton. XPL image, 2x (Field of view = 7mm)	K-feldspar-kalsilite intergrowth. Synnyrite from Synnyr pluton. XPL image, 2x (Field of view = 7mm)
K-feldspar-kalsilite intergrowth. Synnyrite from Synnyr pluton. XPL image, 10x (Field of view = 2mm)	K-feldspar-kalsilite intergrowth. Synnyrite from Synnyr pluton. PPL image, 10x (Field of view = 2mm)	K-feldspar-kalsilite intergrowth. Synnyrite from Synnyr pluton. XPL image, 10x (Field of view = 2mm)
K-feldspar-kalsilite intergrowth. Synnyrite from Synnyr pluton. XPL image, 10x (Field of view = 2mm)	K-feldspar-kalsilite intergrowth. Synnyrite from Synnyr pluton. XPL image, 10x (Field of view = 2mm)	K-feldspar-kalsilite intergrowth. Synnyrite from Synnyr pluton. XPL image, 10x (Field of view = 2mm)
K-feldspar-kalsilite intergrowth. Synnyrite from Synnyr pluton. XPL image, 20x (Field of view = 1mm)	K-feldspar-kalsilite intergrowth. Synnyrite from Synnyr pluton. XPL image, 20x (Field of view = 1mm)	K-feldspar-kalsilite intergrowth. Synnyrite from Synnyr pluton. XPL image, 20x (Field of view = 1mm)