Litchfieldite is a rare igneous rock

Igneous rock

Igneous rock is one of the three main rock types, the others being sedimentary and metamorphic rock. Igneous rock is formed through the cooling and solidification of magma or lava...

. It is a variety of nepheline syenite

Nepheline syenite

Nephelene syenite is a holocrystalline plutonic rock that consists largely of nepheline and alkali feldspar. The rocks are mostly pale colored, grey or pink, and in general appearance they are not unlike granites, but dark green varieties are also known...

 and is composed of two near pure phases of feldspar

Feldspar

Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....

, albite

Albite

Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi3O8. It is a tectosilicate. Its color is usually pure white, hence...

 and microcline

Microcline

Microcline is an important igneous rock-forming tectosilicate mineral. It is a potassium-rich alkali feldspar. Microcline typically contains minor amounts of sodium. It is common in granite and pegmatites. Microcline forms during slow cooling of orthoclase; it is more stable at lower temperatures...

, with predominance of the first one, plus nepheline

Nepheline

Nepheline, also called nephelite , is a feldspathoid: a silica-undersaturated aluminosilicate, Na3KAl4Si4O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites...

, sodalite

Sodalite

Sodalite is a rich royal blue mineral widely enjoyed as an ornamental gemstone. Although massive sodalite samples are opaque, crystals are usually transparent to translucent...

, cancrinite

Cancrinite

Cancrinite is a complex carbonate and silicate of sodium, calcium and aluminium with the formula Na6Ca2[2|Al6Si6O24]·2H2O. It is classed as a member of the feldspathoid group of minerals; the alkali feldspars that are poor in silica. Yellow, orange, pink, white or even blue, it has a vitreous or...

 and calcite

Calcite

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...

. The mafic

Mafic

Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term is a portmanteau of the words "magnesium" and "ferric". Most mafic minerals are dark in color and the relative density is greater than 3. Common rock-forming mafic minerals include olivine,...

 minerals, when presents, are magnetite

Magnetite

Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...

 and an iron rich biotite

Biotite

Biotite is a common phyllosilicate mineral within the mica group, with the approximate chemical formula . More generally, it refers to the dark mica series, primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more aluminous endmembers...

 (lepidomelane).

Occurrence

The rock was named after its occurrence at Litchfield

Litchfield, Maine

Litchfield is a town in Kennebec County, Maine, United States. The population was 3,110 at the 2000 census.-Geography:According to the United States Census Bureau, the town has a total area of , of which, of it is land and of it is water....

, Maine

Maine

Maine is a state in the New England region of the northeastern United States, bordered by the Atlantic Ocean to the east and south, New Hampshire to the west, and the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast. Maine is both the northernmost and easternmost...

, USA, by Bayley in 1892.

It is a very rare rock and also occurs in Blue Mountain and French River, Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

; Soroy and Val River, Norway

Norway

Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...

; Cevadais, Portugal

Portugal

Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...

; Canaã

Canaã

Canaã is a municipality in the state of Minas Gerais in Brazil. The population as of 2004 is 4,470.-See also:* List of municipalities in Minas Gerais...

, Boca Nova, Itajú da Colonia and Peixes, Brazil

Brazil

Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

.

Petrology

Besides the mineral composition litchfieldites are characterized by one or more of the following structures:

• A gneiss
  Gneiss
  Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...
  
  ic appearance due the alternation of leucocratic and mafic bearing mineral bands;
• A foliated
  Foliation
  In mathematics, a foliation is a geometric device used to study manifolds, consisting of an integrable subbundle of the tangent bundle. A foliation looks locally like a decomposition of the manifold as a union of parallel submanifolds of smaller dimension....
  
   appearance, due to preferred orientation of platey minerals like lepidomelane biotite,
• Parallel orientation of the optical axis
  Optical axis
  An optical axis is a line along which there is some degree of rotational symmetry in an optical system such as a camera lens or microscope.The optical axis is an imaginary line that defines the path along which light propagates through the system...
  
   of minerals like nepheline.
• Occurrence within zoned bodies, enveloped by amphibole bearing syenites and quartz-syenites rocks,
• Broken and/or bent twin
  Crystal twinning
  Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals....
  
   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
  Metamorphism
  Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
  
   belt as elongated bodies parallel to the regional structures,
• Isotopic age according to the regional metamorphism

Origin

There are two hypotheses for the origin of these rocks:

1) A pre-tectonic magmatic nepheline syenite

2) A synorogenic

Orogeny

Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...

 intrusion of neheline syenite

Both schools of thought are in accordance that rocks like litchfieldite owe their mineral and structural characteristics to the metamorphism.

Economy

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.

Boca Nova

• Location: Pará State
• Age and determination method
  • Country rocks last metamorphism age: 900 to 600 my (Brazilian cycle)
  • Nepheline syenite rocks: 580+/-10 my- K-Ar, biotite; 724 +/- 30 my- Rb-Sr, whole-rock
• Rocks and minerals presents (between parenthesis when accessory)
  • Alkaline rocks
    • nepheline syenite gneiss (mainly litchfieldite): nepheline, albite, microcline, perthite, dark green biotite, (calcite), (white mica), (zircon), (pyrochlore), (cancrinite), (sodalite), (opaque minerals)
    • Pegmatites-the same mineralogical composition but poorer in biotite.
  • Country rocks: Phyllite
    Phyllite
    Phyllite is a type of foliated metamorphic rock primarily composed of quartz, sericite mica, and chlorite; the rock represents a gradation in the degree of metamorphism between slate and mica schist. Minute crystals of graphite, sericite, or chlorite impart a silky, sometimes golden sheen to the...
    
    , schist
    Schist
    The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...
    
     with subordinated granite
    Granite
    Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
    
    
• Metamorphic grade of country rock: High greenschist facies to medium amphibolite facies
• 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

Canaã

• 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):
  • Alkaline rocks:
    • Litchfieldites: Albite (An=5%), microcline, nepheline, cancrinite, lepidomelane, magnetite, (zircon), (allanite), (corundum), (sodalite)
    • Alkali syenite: microcline perthite, quartz, pyroxene, brown biotite, (amphibole), (titanite), (apatite), (zircon), (muscovite), (corundum), (molybdenite), (opaques)
    • Nepheline bearing pegmatite vein, parallel and cross cutting the foliation of litchfieldite: Feldspar, nepheline, (magnetite), (biotite), (muscovite), (sodalite), (sulfides), (calcite).
    • Syenite pegmatite: feldspar, corundum, muscovite, (biotite), (blue corundum), (sulfides)
  • 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 belt

(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):
  • Alkaline rocks:
    • Litchfieldite: nepheline, microcline, albite, amphibole, pyroxene, (molybdenite
      Molybdenite
      Molybdenite is a mineral of molybdenum disulfide, MoS2. Similar in appearance and feel to graphite, molybdenite has a lubricating effect that is a consequence of its layered structure. The atomic structure consists of a sheet of molybdenum atoms sandwiched between sheets of sulfur atoms...
      
      ), (garnet
      Garnet
      The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" may come from either the Middle English word gernet meaning 'dark red', or the Latin granatus , possibly a reference to the Punica granatum , a plant with red seeds...
      
      ), (titanite
      Titanite
      Titanite, or sphene , is a calcium titanium nesosilicate mineral, CaTiSiO5. Trace impurities of iron and aluminium are typically present...
      
      ), (pyrochlore
      Pyrochlore
      Pyrochlore 2Nb2O6 is a solid solution between the niobium end member , and the tantalum end member .-Occurrence:...
      
      ), (corundum), (sodalite).
    • Syenite and quartz-syenites:
    • Alkaline pegmatite
      Pegmatite
      A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....
      
      s: albite, nepheline, pyroxene, magnetite, zircon, (pyrochlore
      Pyrochlore
      Pyrochlore 2Nb2O6 is a solid solution between the niobium end member , and the tantalum end member .-Occurrence:...
      
      ), (monazite
      Monazite
      Monazite is a reddish-brown phosphate mineral containing rare earth metals. It occurs usually in small isolated crystals. There are actually at least four different kinds of monazite, depending on relative elemental composition of the mineral:...
      
      ), (allanite
      Allanite
      Allanite is a sorosilicate group of minerals within the broader epidote group that contain a significant amount of rare earth elements. The mineral occurs mainly in metamorphosed clay rich sediments and felsic igneous rocks...
      
      ), (corundum
      Corundum
      Corundum is a crystalline form of aluminium oxide with traces of iron, titanium and chromium. It is a rock-forming mineral. It is one of the naturally clear transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red...
      
      ).
  • Country rocks: granitic gneisses, amphibolites
• Metamorphic grade of country rock: high amphibolite
• Geometry of the alkaline body: A belt of elonganted 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 Bahia

(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)
  • Nepheline syenite rocks: 732 +/- 8 my, U-Pb, titanite
• 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
• Proposed origin: Metamorphic synorogenic alkaline rocks.