Napoleonite from Corsica. (cut & polished surface; ~12.3 centimeters across at its widest)
This distinctive rock is an orbiculite, an igneous rock having an orbicular texture. Orbiculites have orbicles, subspherical masses that crystallized in the parent magma before final solidification. They usually have both concentric layering and radiating crystals.
Orbicular rocks have long been noticed on the island of Corsica in the Mediterranean Sea - they are nicknamed "corsite" or "napoleonite" (Napoleon was born there). Napoleonite is often mis-referred to as "orbicular diorite", but it's actually an orbicular gabbro - it has 46% silica (= mafic chemistry, not intermediate). It is dominated by calcium-rich plagioclase feldspar and amphibole. Some of the amphibole is reported to be paramorphic after pyroxene. "Paramorphic" refers to a mineral that has changed its molecular structure, but the external form and chemical composition have not changed.
Napoleonite has been used as a decorative stone (countertop stone & carved-n-polished objects).
Location: undisclosed / unrecorded site on the island of Corsica, Mediterranean Sea
-----------------------------
Partly synthesized from:
Hatch et al. (1972) - Petrology of the Igneous Rocks. London. Thomas Murby & Co. 551 pp.
Price (2007) - The Sourcebook of Decorative Stone, an Illustrated Identification Guide. Buffalo, New York. Firefly Books. 288 pp.
-----------------------------
Info. at:
en.wikipedia.org/wiki/Napoleonite
and
www.mindat.org/min-53501.html
Tags: napoleonite corsite orbiculite orbicular igneous rock rocks gabbro Corsica
Napoleonite from Corsica. (cut & polished surface; ~12.3 centimeters across at its widest)
This distinctive rock is an orbiculite, an igneous rock having an orbicular texture. Orbiculites have orbicles, subspherical masses that crystallized in the parent magma before final solidification. They usually have both concentric layering and radiating crystals.
Orbicular rocks have long been noticed on the island of Corsica in the Mediterranean Sea - they are nicknamed "corsite" or "napoleonite" (Napoleon was born there). Napoleonite is often mis-referred to as "orbicular diorite", but it's actually an orbicular gabbro - it has 46% silica (= mafic chemistry, not intermediate). It is dominated by calcium-rich plagioclase feldspar and amphibole. Some of the amphibole is reported to be paramorphic after pyroxene. "Paramorphic" refers to a mineral that has changed its molecular structure, but the external form and chemical composition have not changed.
Napoleonite has been used as a decorative stone (countertop stone & carved-n-polished objects).
Location: undisclosed / unrecorded site on the island of Corsica, Mediterranean Sea
-----------------------------
Partly synthesized from:
Hatch et al. (1972) - Petrology of the Igneous Rocks. London. Thomas Murby & Co. 551 pp.
Price (2007) - The Sourcebook of Decorative Stone, an Illustrated Identification Guide. Buffalo, New York. Firefly Books. 288 pp.
-----------------------------
Info. at:
en.wikipedia.org/wiki/Napoleonite
and
www.mindat.org/min-53501.html
Tags: napoleonite corsite orbiculite orbicular igneous rock rocks gabbro Corsica
Napoleonite from Corsica. (crack surface; ~7.3 centimeters across at its widest)
This rock is an orbiculite, an igneous rock having an orbicular texture. Orbiculites have orbicles, subspherical masses that crystallized in the parent magma before final solidification. They usually have both concentric layering and radiating crystals.
Orbicular rocks have long been noticed on the island of Corsica in the Mediterranean Sea - they are nicknamed "corsite" or "napoleonite" (Napoleon was born there). Napoleonite is often mis-referred to as "orbicular diorite", but it's actually an orbicular gabbro - it has 46% silica (= mafic chemistry, not intermediate). It is dominated by calcium-rich plagioclase feldspar and amphibole. Some of the amphibole is reported to be paramorphic after pyroxene. "Paramorphic" refers to a mineral that has changed its molecular structure, but the external form and chemical composition have not changed.
Napoleonite has been used as a decorative stone (countertop stone & carved-n-polished objects).
Location: undisclosed / unrecorded site on the island of Corsica, Mediterranean Sea
-----------------------------
Partly synthesized from:
Hatch et al. (1972) - Petrology of the Igneous Rocks. London. Thomas Murby & Co. 551 pp.
Price (2007) - The Sourcebook of Decorative Stone, an Illustrated Identification Guide. Buffalo, New York. Firefly Books. 288 pp.
-----------------------------
Info. at:
en.wikipedia.org/wiki/Napoleonite
and
www.mindat.org/min-53501.html
Tags: napoleonite corsite orbiculite orbicular igneous rock rocks gabbro Corsica
(cut & polished surface; ~7.7 centimeters across at its widest)
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Rodingite is a type of metasomatic rock. "Metasomatism" refers to metamorphism principally by chemical change (other causative agents of metamorphism are heat and pressure). Rodingite forms when mafic igneous rocks (such as gabbros) are chemically altered by serpentinization of a nearby mass of peridotite. The chemical change is principally by the addition of calcium (Ca+2), which gets expelled from serpentinized peridotite bodies. Rodingite mineralogy is variable, but typically includes calcic pyroxene and various types of garnet, such as grossular and hydrogrossular.
The rodingite seen here is from the Canari area of Corsica. A large chrysotile asbestos mine operated in the area from the late 1940s to the mid-1960s. Asbestos occurs in a serpentinized peridotite body, with surrounding units including greenschists, metamorphosed gabbros, and metamorphosed pyroxenites. Minerals reported in the rodingites around the serpentinite mass include grossular garnet, hessonite garnet, andradite garnet, chromiferous garnet, diopside pyroxene, vesuvianite, calcite, wollastonite, epidote, and chlorite (Goujou, 1998).
The rocks in this area of Corsica are part of an ophiolite complex. Ophiolites are sections of oceanic lithosphere (basaltic / gabbroic crustal rocks + ultramafic upper mantle rocks) that have been metamorphosed and plastered onto the edges of continental lithosphere, usually by obduction (the opposite of subduction). The protoliths of the Corsica ophiolite rocks are Jurassic-aged oceanic lithospheric rocks and overlying sediments. Tectonic rifting and the formation of mafic oceanic lithosphere started at about 160 million years ago, during the Middle to Late Jurassic. Metamorphism of these rocks occurred during the late Mesozoic to Tertiary. What was originally mantle peridotite is now asbestos-bearing serpentinite. Rodingite formation in the area also dates to the late Mesozoic to Tertiary.
Geologic unit: Schistes Lustres Complex (Jurassic-aged protolith & Cretaceous- to Tertiary-aged metamorphism)
Locality: unrecorded / undisclosed site at or near the town of Canari / at or near the Canari Mine, western side of Cape Corsica, northeastern Corsica (Alpine Corsica), Mediterranean Sea
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Info. mostly synthesized from:
Goujou (1998) - Minéralogie des rodingites de la mine de Canari, Corse, France. Le Règne Minéral 20: 11-24.
Robertson (1999) - British Gelogical Survey Rock Classificaiton Scheme, Volume 2, Classification of Metamorphic Rocks. 24 pp.
Marroni & Pandolfi (2003) - Deformation history of the ophiolite sequence from the Balagne Nappe, northern Corsica: insights in the tectonic evolution of Alpine Corsica. Geological Journal 38: 67-83.
----------------------------------
Info. at:
en.wikipedia.org/wiki/Rodingite
and
en.wikipedia.org/wiki/Metasomatism
Tags: rodingite metasomatism metasomatite grossular garnet diopside pyroxene chlorite epidote Canari Corsica Alpine Jurassic protolith Mesozoic Cretaceous Tertiary metamorphism metamorphic rock rocks ophiolite ophiolites Schistes Lustres Complex
(cut & polished surface; ~7.7 centimeters across at its widest)
----------------------------------
Rodingite is a type of metasomatic rock. "Metasomatism" refers to metamorphism principally by chemical change (other causative agents of metamorphism are heat and pressure). Rodingite forms when mafic igneous rocks (such as gabbros) are chemically altered by serpentinization of a nearby mass of peridotite. The chemical change is principally by the addition of calcium (Ca+2), which gets expelled from serpentinized peridotite bodies. Rodingite mineralogy is variable, but typically includes calcic pyroxene and various types of garnet, such as grossular and hydrogrossular.
The rodingite seen here is from the Canari area of Corsica. A large chrysotile asbestos mine operated in the area from the late 1940s to the mid-1960s. Asbestos occurs in a serpentinized peridotite body, with surrounding units including greenschists, metamorphosed gabbros, and metamorphosed pyroxenites. Minerals reported in the rodingites around the serpentinite mass include grossular garnet, hessonite garnet, andradite garnet, chromiferous garnet, diopside pyroxene, vesuvianite, calcite, wollastonite, epidote, and chlorite (Goujou, 1998).
The rocks in this area of Corsica are part of an ophiolite complex. Ophiolites are sections of oceanic lithosphere (basaltic / gabbroic crustal rocks + ultramafic upper mantle rocks) that have been metamorphosed and plastered onto the edges of continental lithosphere, usually by obduction (the opposite of subduction). The protoliths of the Corsica ophiolite rocks are Jurassic-aged oceanic lithospheric rocks and overlying sediments. Tectonic rifting and the formation of mafic oceanic lithosphere started at about 160 million years ago, during the Middle to Late Jurassic. Metamorphism of these rocks occurred during the late Mesozoic to Tertiary. What was originally mantle peridotite is now asbestos-bearing serpentinite. Rodingite formation in the area also dates to the late Mesozoic to Tertiary.
Geologic unit: Schistes Lustres Complex (Jurassic-aged protolith & Cretaceous- to Tertiary-aged metamorphism)
Locality: unrecorded / undisclosed site at or near the town of Canari / at or near the Canari Mine, western side of Cape Corsica, northeastern Corsica (Alpine Corsica), Mediterranean Sea
----------------------------------
Info. mostly synthesized from:
Goujou (1998) - Minéralogie des rodingites de la mine de Canari, Corse, France. Le Règne Minéral 20: 11-24.
Robertson (1999) - British Gelogical Survey Rock Classificaiton Scheme, Volume 2, Classification of Metamorphic Rocks. 24 pp.
Marroni & Pandolfi (2003) - Deformation history of the ophiolite sequence from the Balagne Nappe, northern Corsica: insights in the tectonic evolution of Alpine Corsica. Geological Journal 38: 67-83.
----------------------------------
Info. at:
en.wikipedia.org/wiki/Rodingite
and
en.wikipedia.org/wiki/Metasomatism
Tags: rodingite metasomatism metasomatite grossular garnet diopside pyroxene chlorite epidote Canari Corsica Alpine Jurassic protolith Mesozoic Cretaceous Tertiary metamorphism metamorphic rock rocks ophiolite ophiolites Schistes Lustres Complex