leucite

There was the girl of shallow virtue on Leucite.

Rocks containing leucite are scarce, many countries such as England being entirely without them.

They resemble leucite in their shape, but have not yet been proved to have its crystalline outlines.

Leucite is common in lavas but very rare in plutonic rocks.

This pseudo-cubic character of leucite is very similar to that of the mineral boracite.

Melanite is found in some of the lavas, as in the leucite syenites.

The leucite is often present in two sets of crystals, both porphyritic and as an ingredient of the ground mass.

They are black or ashy-grey in color, often vesicular, and may contain many large grey phenocysts of leucite.

By far the greater number of the rocks which contain leucite are lavas of Tertiary or recent geological age.

They are rich in leucite, but contain also some sanidine and often much nepheline with hauyne or nosean.

They may be of considerable size like the grey, rounded leucite crystals found on the sides of Vesuvius.

Other minerals occurring in the rock include sanidine, andradite, fassaite, leucite and hauyne.

It occurs naturally in the minerals leucite, pollucite, carnallite, zinnwaldite, and lepidolite.

The former consist mainly of plagioclase, leucite and augite, while the latter contain olivine in addition.

It is associated with other minerals typical of undersaturated environments, namely leucite, cancrinite and natrolite.

Rocks that contain leucite or nepheline, either partly or wholly replacing felspar, are not included in this table.

Leucite is present in the K-rich, silica-poor Latium pozzolanas.

Their commonest minerals are olivine, anorthite, hornblende, augite, biotite and leucite.

They are of trachytic appearance, containing phenocysts of sanidine, leucite, augite and biotite.

They are associated principally with basalts, nepheline and leucite basalts and monchiquites.

Geology and Geochemistry of the Leucite Hills Volcanic Field.

Mineral assembly is usually abundant feldspathoids (leucite or nepheline), plagioclase, and lesser alkali feldspar.

It commonly occurs in association with orthoclase, sanidine, labradorite, olivine, leucite, amphiboles and other pyroxenes.

Nepheline decreases in amount as leucite increases since the abundances of the two reflect the Na:K ratio of the rock.

Other localities for this group are at Julianehaab in Greenland with sodalite-syenite; at their margins they contain pseudomorphs after leucite.