Foidolite with Hauyne

Foidolites are coarse-grained intrusive igneous rock with a feldspathoid mineral content greater than 60%. On the APF diagram, these rocks plot in the corner closest to F. The term "foidolite" is too general and, wherever possible, should be replaced with a name that clarifies which of the feldspathoid minerals is predominant and whether other minerals are present in any significant amount. For example, nephelinolites are foidolites comprising mostly nepheline; they can be further categorized as melteigite, ijolite or urtite depending on the relative proportion of dark-colored minerals (most of all, clinopyroxene and biotite) in their composition. The volcanic equivalents are termed foidite and phonolitic or tephritic foidites. According to the mineralogy can be divided into:

- Ferusite (for Fergus, Montana, USA): A variety of foidolite containing essential clinopyroxene and 30-70% modal leucite (typically replaced by a mixture of nepheline, alkali feldspar, kalsilite and analcime).
- Ijolite (For Iijoki, northern Finland.): A variety of foidolite containing essential clinopyroxene (diopside, aegirine-augite or aegirine) and 30-70% modal nepheline.
- Italite (For Italy): A variety of foidolite in which leucite is the predominant feldspathoid mineral and ferromagnesian silicates comprise 30 modal % or less of the rock.
- Melilitite (for Melteig, Norway) A collective name for extrusive and shallow intrusive rocks containing > 10% modal melilite.
- Missourite (For Missouri, USA) A variety of foidolite containing essential clinopyroxene and 10-30% modal leucite; olivine is also commonly present.
- Tawite (for Tavajok, Lovozero Mts., Kola P-la, northwestern Russia) A variety of foidolite in which sodalite is the predominant feldspathoid mineral.
- Urtite (for For Lujavr Urt, (Lovozero Mts.), Kola P-la, northwestern Russia) A variety of foidolite containing > 70% modal nepheline; clinopyroxene, apatite, titanite, magnetite and perovskite are commonly present in subordinate amounts.

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
Hauyne (with small fluid inclusions) and sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)	Hauyne (with small fluid inclusions) and sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)	Hauyne (with small fluid inclusions) and sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)
Hauyne (with small fluid inclusions) and sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)	Hauyne (with small fluid inclusions) and sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)	Hauyne (with small fluid inclusions) and sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)
Hauyne (with small fluid inclusions) and sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)	Hauyne (always dark) and sanidine (I order gray). Laacher See (Germany). XPL image, 2x (Field of view = 7mm)	Hauyne (with small fluid inclusions) and sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)
Hauyne (with small fluid inclusions) and sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)	Hauyne (with small fluid inclusions) and sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)	Hauyne (with small fluid inclusions) and sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)