Monzonite

Monzonite is an igneous intrusive rock. It is composed of approximately equal amounts of plagioclase and alkali feldspar, with less than 5% quartz by weight. It may contain minor amounts of hornblende, biotite and other minerals. If quartz constitutes greater than 5%, the rock is termed a quartz monzonite. Latite or trachyandesite are the approximate volcanic equivalents of monzonite. Monzonite was originally named after the Monzoni range in Val di Fassa (Trento Province - Italy).
Monzonite is a relatively uncommon rock type. It usually does not form its own plutons. Monzonitic magma most likely forms only a part of a generally more acidic (granitic) intrusions.

a great variety of names (now all Obsolete) have been attributed in time to these rocks:

Windsorite: Obsolete name for a light-colored quartz-monzonite aplite with minor amount of Biotite. named by Daly in 1903 after Windsor, Vermont, USA
Ukrainite: A local name for Quartz-monzonite; from type locality in Ukraine
Masanite: A Quartz-monzonite containing phenocrysts of zoned plagiolcase and corroded quartz in a granophyric groundmass. Name given by Koto (1909) from Masan-po, Korea
Sörkedalite: A local name for a variety of Olivine monzodiorite consisting of abundant antiperthitic andesine, mantled by anorthoclase, and by olivine; minor amount of clino-pyroxene and biotite may be present. From Sorkedal, Oslo, Norway.
Larvikite: A variety of augite syenite or monzonite consisting of rhombshaped ternary feldspars (with a distinctive schiller), from Larvik, Oslo Igneous Province, Norway.
Vallevarite: An obsolete local name for a variety of anorthosite, consisting essentially of andesine and microcline antiperthite with minor diopside and biotite. From Vallevara, Sweden.
Amherstite: A leucocratic variety of quartz belonging to the charnockitic rock series. The rock consists essentially of andesine-microcline antiperthite with minor quartz and hypersthene. From Amherst County, Virginia,USA.
Kjelsaite: A local name given to a plagioclase-rich larvikite which is a variety of augite syenite or monzonite. From Kjelsas, Oslo district, Norway.

englishmonzonite.jpg

QAPF Diagram Monzonite field in blue.




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Monzonite sample (plagioclase white, Alkali feldspar pink and femic minerals).




Bibliography



• Eric A.K.Middlemost (1985): Magmas and Magmatic Rocks. Longman, London
• Ron H. Vernon (2004): A pratical guide to rock microstructure. Cambridge editore
• K.G.Cox, J.D.Bell & R.J Pankhurst (1979): The interpretetion of igneous rocks. George Allen&Unwin editori.
• David Shelley (1983): Igneous and metamorphic rocks under the microscope. Campman & Hall editori


Photo
monzonite(monzoni)(1).jpg

Orthoclase (altered by sericite), biotie (brown), magnetite (black) and pyroxene crystals in a monzonite from Monzoni massif, Italy. PPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(2).jpg

Orthoclase (I order gray), biotie, magnetite (black) and pyroxene (high interference colors) crystals in a monzonite from Monzoni massif, Italy. XPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(3).jpg

Orthoclase (altered by sericite), biotie (brown), magnetite (black) and pyroxene crystals in a monzonite from Monzoni massif, Italy. PPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(4).jpg

Orthoclase (I order gray), biotie, magnetite (black) and pyroxene (high interference colors) crystals in a monzonite from Monzoni massif, Italy. XPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(5).jpg

Orthoclase (altered by sericite), biotie (brown), magnetite (black) and pyroxene crystals in a monzonite from Monzoni massif, Italy. PPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(6).jpg

Orthoclase (I order gray), biotie, magnetite (black) and pyroxene (high interference colors) crystals in a monzonite from Monzoni massif, Italy. XPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(7).jpg

Biotie (brown), magnetite (black) and pyroxene crystals in a monzonite from Monzoni massif, Italy. PPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(8).jpg

Biotie, magnetite (black) and pyroxene (high interference colors) crystals in a monzonite from Monzoni massif, Italy. XPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(9).jpg

Orthoclase (altered by sericite), biotie (brown), magnetite (black) and pyroxene crystals in a monzonite from Monzoni massif, Italy. PPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(10).jpg

Orthoclase (I order gray), biotie, magnetite (black) and pyroxene (high interference colors) crystals in a monzonite from Monzoni massif, Italy. XPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(11).jpg

Biotie, magnetite (black) and pyroxene (high interference colors) crystals in a monzonite from Monzoni massif, Italy. XPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(12).jpg

Orthoclase (altered by sericite), biotie (brown), magnetite (black) and pyroxene crystals in a monzonite from Monzoni massif, Italy. PPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(13).jpg

Orthoclase (I order gray), biotie, magnetite (black) and pyroxene (high interference colors) crystals in a monzonite from Monzoni massif, Italy. XPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(14).jpg

Orthoclase (altered by sericite) and with altered olivine inclusions, biotie (brown), magnetite (black) and pyroxene crystals in a monzonite from Monzoni massif, Italy. PPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(15).jpg

Orthoclase (I order gray) and with altered olivine inclusions, biotie, magnetite (black) and pyroxene (high interference colors) crystals in a monzonite from Monzoni massif, Italy. XPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(16).jpg

Orthoclase (altered by sericite), biotie (brown), magnetite (black) and pyroxene crystals in a monzonite from Monzoni massif, Italy. PPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(17).jpg

Orthoclase (I order gray), biotie, magnetite (black) and pyroxene (high interference colors) crystals in a monzonite from Monzoni massif, Italy. XPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(18).jpg

Orthoclase (altered by sericite), biotie (brown), magnetite (black) and pyroxene crystals in a monzonite from Monzoni massif, Italy. PPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(22).jpg

concentric inclusion in a pyroxene crystal in a monzonite from Monzoni massif, Italy. PPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(23).jpg

concentric inclusion in a pyroxene (high interference colors) crystal in a monzonite from Monzoni massif, Italy. XPL image, 2x (Field of view = 7mm)
monzonite(monzoni)(25).jpg

concentric inclusion in a pyroxene (high interference colors) crystal in a monzonite from Monzoni massif, Italy. XPL image, 10x (Field of view = 2mm)
monzonitee(6).jpg

Orthoclase (I order gray), plagioclase (I order gray with polysynthetic twinning) and clinopyroxene (high interference colors). XPL image, 2x (Field of view = 7mm)
monzonitee(7).jpg

Orthoclase, plagioclase (both colorles) and clinopyroxene (high relief, pale gray-green). PPL image, 2x (Field of view = 7mm)
monzonitee(8).jpg

Orthoclase (I order gray), plagioclase (I order gray with polysynthetic twinning) and clinopyroxene (high interference colors). XPL image, 2x (Field of view = 7mm)
monzonitee(9).jpg

Orthoclase, plagioclase (both colorles), hornblende (green) and clinopyroxene (high relief, pale gray-green). PPL image, 2x (Field of view = 7mm)
monzonitee(10).jpg

Orthoclase (I order gray), plagioclase (I order gray with polysynthetic twinning) and clinopyroxene (high interference colors). XPL image, 2x (Field of view = 7mm)
monzonitee(11).jpg

Orthoclase (I order gray), plagioclase (I order gray with polysynthetic twinning) and clinopyroxene (high interference colors). XPL image, 2x (Field of view = 7mm)
monzonitee(12).jpg

Orthoclase (I order gray), plagioclase (I order gray with polysynthetic twinning) and clinopyroxene (high interference colors). XPL image, 2x (Field of view = 7mm)
monzonitee(13).jpg

Zoned plagioclase. XPL image, 2x (Field of view = 7mm)
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Zoned plagioclase. XPL image, 2x (Field of view = 7mm)
monzonite2012(2).jpg

Sericitized plagioclase and pyroxene. XPL image, 2x (Field of view = 7mm)
monzonite2012(3).jpg

Sericitized plagioclase and pyroxene. XPL image, 2x (Field of view = 7mm)
monzonite2012(4).jpg

Sericitized plagioclase and pyroxene. XPL image, 2x (Field of view = 7mm)
monzonite2012(5).jpg

Sericitized plagioclase and pyroxene. XPL image, 2x (Field of view = 7mm)
monzonite2012(6).jpg

Sericitized plagioclase and pyroxene. XPL image, 2x (Field of view = 7mm)
monzonite2012(7).jpg

Sericitized plagioclase and pyroxene. XPL image, 2x (Field of view = 7mm)