Monzodiorite

monzodiorite is a coarse-grained igneous rock consisting of essential plagioclase feldspar, orthoclase feldspar, hornblende, and biotite, with or without pyroxene. Plagioclase is the dominant feldspar making up 60–90% of the total feldspar and varying from oligoclase to andesine in composition. The presence of the orthoclase feldspar distinguishes this rock from a diorite.

Orbicular monzodiorite. The orbs are composed of radiating augite and hornblende crystals. The light-colored, interorbicle material is a mixture of plagioclase feldspar and microcline feldspar, plus minor quartz. North Carolina, USA. From James St. John

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
Poikilitic orthoclase with plagioclase, biotite and pyroxene inclusions. PPL image, 2x (Field of view = 7mm)	Poikilitic orthoclase with plagioclase, biotite and pyroxene inclusions. XPL image, 2x (Field of view = 7mm)	Plagioclase, pyroxene and interstitial orthoclase. XPL image, 2x (Field of view = 7mm)
Plagioclase, pyroxene and interstitial orthoclase. XPL image, 2x (Field of view = 7mm)	Plagioclase, pyroxene and interstitial orthoclase. XPL image, 2x (Field of view = 7mm)	Plagioclase, pyroxene and interstitial orthoclase. XPL image, 2x (Field of view = 7mm)
Plagioclase, pyroxene and interstitial orthoclase. XPL image, 2x (Field of view = 7mm)	Plagioclase, pyroxene and interstitial orthoclase. XPL image, 2x (Field of view = 7mm)	Plagioclase, pyroxene and interstitial orthoclase. XPL image, 2x (Field of view = 7mm)