PSEUDOLEUCITE

Pseudoleucite is a pseudomorph of nepheline + orthoclase over the original leucite.

The typical cubic form of leucite, the trapezohedron, may be preserved, but generally only rounded forms are observed.

Leucite is typical of K-rich and silica-deficient volcanic rocks, almost exclusively occurring as phenocryst in undersaturated (mafic and alkaline) volcanic and hypabyssal rocks, such as monzosyenites, trachytes, trachyandesites, phonolites, basanites, leucitites, melilitites, lamproites and lamprophyres..

Pseudoleucite 01: In PPL, in the certer of the image, idiomorphic crystal of pseudoleucite in phonolite. Pseudoleucite consists of a chaotic intergrowth of small crystals that tend to lamellar and whose identification is not possible under the petrographic microscope. There is a sharp zonation, with a darker core and lighter edges.
Pseudoleucite 01: The same section as of the previous image, now in XPL. The crystals that make up the pseudoleucite are very small and cannot be identified under the microscope.
In XPL, detail view of a pseudoleucite. Below, darker, the matrix of the rock. Diagonally, lighter, the edge of the pseudoleucite. Top left, in yellowish to greenish tones, the nucleus of the pseudoleucite.