The rock was named after its occurrence at Litchfield, Maine, USA, by Bayley in 1892.[3][4]
It is a very rare rock and also occurs in Blue Mountain and French River, Canada;[4] Soroy and Val River, Norway; Cevadais, Portugal; Canaã,[5] Boca Nova, Itajú da Colonia and Peixes, Brazil.
Petrologyedit
Besides the mineral composition litchfieldites are characterized by one or more of the following structures:
A gneissic appearance due to the alternation of leucocratic and mafic bearing mineral bands;
A foliated appearance, due to preferred orientation of platey minerals like lepidomelane biotite,
Parallel orientation of the optical axis of minerals like nepheline.
Occurrence within zoned bodies, enveloped by amphibole bearing syenites and quartz-syenites rocks,
Broken and/or bent twin lamellae in plagioclase (albite),
Mortar structure,
Biotite with kink banding structure and bent cleavage planes,
Occurrence as large boudin or scattered blocks at the surface,
Occurrence within metamorphic belt as elongated bodies parallel to the regional structures,
Isotopic age according to the regional metamorphism
Originedit
There are two hypotheses for the origin of these rocks:
Both schools of thought are in accordance that rocks like litchfieldite owe their mineral and structural characteristics to the metamorphism.
Economyedit
Due to the content of alkali elements and alumina, they are very important ore for the glass industry. The iron-bearing minerals when present are strongly magnetic and can be removed through a magnetic field.
Occurrences of nepheline syenite gneisses in Braziledit
Boca Novaedit
Location: Pará State
Age and determination method
Country rock last metamorphism age: 900 to 600 my (Brazilian cycle)
Geometry of the alkaline body :Boulders scattered. Geophysical dates suggests elongated bodies parallel to the regional structures.
Textures and structures presents in alkaline rocks: Gneissose appearance; folded foliation; foliation parallel to the country rocks; preferential orientation of biotites parallel to the gneissic band; pegmatites veins with pinch and swell structure parallel and cross cutting the foliation; biotite crystal with kink banding structure; plagioclase with bent twin lamella; feldspar with peristherite; oriented optical axis in nephelines;
Proposed origin: metamorphism of igneous nepheline syenite
Canaãedit
Localization: Rio de Janeiro State
Age and determination method
Country rocks last metamorphism age: 900 to 600 my (Brazilian cycle)
Nepheline syenite rocks: 542 +/-14 my Rb-Sr whole rock; 424 +/- 13 my K-Ar in biotite.
Rocks and minerals (between parenthesis when accessory):
Country rocks: Biotite-sillimanite-gneiss, amphibolites, migmatites, (granite).
Metamorphic grade of country rock: high anphibolite facies
Geometry of the alkaline body: elongated and concordant bodies
Textures and structures presents in alkaline rocks: gneissose appearance, parallel to the country rock foliation; oriented biotite and feldspar; plagioclase with bent twin lamella; kink-banding biotite; oriented optical axis in nephelines; zoned bodies-litchfieldite in center and syenites surrounding.
Proposed origin: metamorphism of igneous nepheline syenite.
Tocantins nepheline syenite gneiss beltedit
(Estrela, Eldorado, Porto Nacional, Peixe)
Localization: Tocantins State
Age and determination method:
Country rocks last metamorphism age: 900 to 600 my (Brazilian cycle)
Nepheline syenite rocks: 1,5 Gy
Rocks and minerals (between parenthesis when accessory):
Metamorphic grade of country rock: high amphibolite
Geometry of the alkaline body: A belt of elongated zoned bodies parallel to the regional structures.
Textures and structures presents in alkaline rocks: gneissose appearance, foliation, preferred orientation of biotite crystals, faults, boudinage, plagioclase with bent twin lamella; feldspar with peristherite, plagioclase with undulose extinction.
Proposed origin: Metamorphism and metasomatism of igneous nepheline syenite rocks.
Alkaline Rocks Province of South Bahiaedit
(Itaju da Colonia, Santa Cruz da Vitória, Potiriguá, Itabuna)
Localization: Bahia State
Age and determination method:
Country rocks last metamorphism age: 900 to 600 my (Brazilian cycle)
Rocks and minerals (between parenthesis when accessory):
Alcalines rocks:
Litchfieldite: albite, microcline, nepheline, dark green biotite, brown biotite, (pyroxene), (amphibole), (cancrinite), (sodalite)
Tawite: albite, microcline, sodalite, (nepheline)
Syenite
Alkaline pegmatites
Country rocks: granitic gneiss, migmatite, granulite
Metamorphic grade of country rock: High amphibolite facies
Geometry of the alkaline body: elongated bodies parallel to regional structures.
Textures and structures present in alkaline rocks: elongated and oriented cluster (schlieren) of mafic minerals, plagioclase with bent and broken twin lamella, biotite and muscovite orientation (foliation), mortar structures, kink-banding in biotite
^Le Maitre, R.W. (2002) Igneous Rocks - A Classification and Glossary of Terms, 2nd edition, Cambridge, Cambridge University Press, page 105. ISBN 0-521-66215-X
^Robins, B. and Tysseland, M. (1979) Fenitization of some mafic igneous rocks in the Seiland province, northern Norway Archived 2015-09-24 at the Wayback Machine, Norsk Geologisk Tidsskrift, Volume 59 Number 1 pages 1-23, page 3. Retrieved 2015-07-20.
^Litchfieldite and the Litchfield Sodalite Locality, Maine Geological Survey
^ abWilliams, Howel, Francis J. Turner and Charles M. Gilbert, Petrography, Freeman, 1954, p. 117
^Industrial Minerals & Rocks, Society for Mining, Metallurgy, and Exploration; 7th ed. 2006, p. 661 ISBN 978-0-87335-233-8