Sodalite In Thin Section

Sodalite in a nepheline syenite.

Sodalite in thin section. Sodalite is a feldspathoid mineral a chloride containing sodium aluminosilicate that occurs with leucite nepheline cancrinite in such igneous rocks as nepheline syenite trachyte and phonolite. Click on the image to see the crystal under crossed polars. This is called incomplete extinction or sometimes birds eye maple extinction.

Sodalite colorless and transparent in thin section but frequently pale blue in the hand specimens is the principal feldspathoid mineral in addition to nepheline. This means that biotite in standard thin sections rarely goes completely extinct. Damage produced during thin section grinding causes speckles of light in the biotite where the crystal lattice has been deformed.

Crystals rare typically dodecahedra to 10 cm. Click on the image to view this thin section under crossed polars. This hexagonal crystal is oriented with its optic axis vertical.

The name is derived from composition its contains sodium soda na. Sodalite na8al6si6o24cl2 c 2001 mineral data publishing version 1 2 crystal data. On f111g common forming pseudohexagonal prisms by.

Sodalite na 8 al 6 si 6 o 24 cl 2 named from its chemical composition sodalite was discovered in 1811 in the ilimaussaq intrusive complex in greenland. Extremely iron rich olivine is rare but is present in some nepheline syenite. Nepheline k 21 is colorless when viewed under plane polarized light.

The soldalite group feldspathoids are based on the cubic structure which is a tektosilicate framework.