Litchfieldite is a rare igneous rock. It is a coarse-grained, foliated variety of nepheline syenite, sometimes called nepheline syenite gneiss or gneissic nepeheline syenite. Litchfieldite is composed of two varieties of feldspar (mostly albite but also some microcline), with nepheline, sodalite, cancrinite and calcite. The mafic minerals, when present, are magnetite and an iron-rich variety of biotite (lepidomelane).

Occurrence

The rock was named after its occurrence at Litchfield, Maine, USA, by Bayley in 1892. It is a very rare rock and also occurs in Blue Mountain and French River, Canada; Soroy and Val River, Norway; Cevadais, Portugal; Canaã, Boca Nova, Itajú da Colonia and Peixes, Brazil.

Petrology

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

Origin

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.

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.

Occurrences of nepheline syenite gneisses in Brazil

Boca Nova

Canaã

Tocantins nepheline syenite gneiss belt

(Estrela, Eldorado, Porto Nacional, Peixe)

Alkaline Rocks Province of South Bahia

(Itaju da Colonia, Santa Cruz da Vitória, Potiriguá, Itabuna)