In mineral composition they scarcely differ from the lavas of Somma, the rock consisting of a base of leucite and augite, through which large crystals of augite and some of leucite are scattered.
On penetrating still deeper, we can detect the constituent parts by the naked eye, and in the Vesuvian currents distinct crystals of augite and leucite become apparent.
This pseudo-cubic character of leucite is exactly the same as that of the mineral boracite (q.
Leucite lavas from which felspar is absent are divided into the leucitites and leucite basalts.
By far the greater number of the rocks which contain leucite are lavas of Tertiary or recent geological age.
Leucite is very often accompanied by nepheline, sodalite or nosean; other minerals which make their appearance with some frequency are melanite, garnet and melilite.
Those leucite rocks which contain abundant essential plagioclase felspar are known as leucite-tephrites and leucite-basanites.
Leucite-monchiquites are fine-grained dark rocks consisting of olivine, titaniferous augite and iron oxides, with a glassy ground mass in which small rounded crystals of leucite are scattered.
The rounded shape of its crystals, their white or grey colour, and rough cleavage, make the presence of leucite easily determinable in many of these rocks by simple inspection, especially when the crystals are large.
Nepheline appears to decrease in amount as leucite increases.
The former consist mainly of plagioclase, leucite and augite, while the latter contain olivine in addition.
Although rocks containing leucite are numerically scarce, many countries such as England being entirely without them, yet they are of wide distribution, occurring in every quarter of the globe.
The leucite is often present in two sets of crystals, both porphyritic and as an ingredient of the ground mass.
In pre-Tertiary rocksleucite is uncommon, since it readily decomposes and changes to zeolites, analcite and other secondary minerals.
Mesa and outlying butte in theLeucite Hills of Wyoming (after Whitman Cross, U.
The leucite lavas of Niedermendig contain hauyne in abundance.
They are chiefly leucite and nepheline rocks, such as leucitite, leucitophyre and nephelinite, but basalt and trachyte also occur.
Defn: An igneous rock consisting essentially of plagioclase and either leucite or nephelite, or both.
An igneous rock consisting essentially of plagioclase and either leucite or nephelite, or both.
Minerals of the felspathoid group occur in a large number of basaltic rocks; nepheline and leucite are the most common, but haüyne is occasionally present.
Leucite-basalts contain small rounded crystals of leucite in place of plagioclase felspar.
Mallard, in 1876, the higher degree of symmetry exhibited by the external form of the crystals is the result of mimetic twinning, as in the pseudo-cubic crystals of leucite (q.
Analcite, leucite and garnet often crystallize in the simple form {211}.
They had very little leucite and abounded in pyroxene and olivine, and sometimes contained a few crystals of amphibole.
These threads were often of a clear yellowish colour, and, when observed under the microscope, were found to consist of very minute crystals of leucite embedded in a homogeneous paste.
If required to give the mineralogical characteristics of this lava, I would say that it was rich inleucite and contained little or no pyroxene; the fragmentary lava, on the contrary, is poor in leucite and rich in pyroxene.
These observations led me to reject the opinion of those who hold that crystals of leucite are pre-existent in the lava.
It is evident, therefore, that crystals of leucite raised to a certain temperature may break, and thus we can understand how almost all Vesuvian ashes contain fragments of the said crystals enveloped in the paste of the lava.
One of the lavas of the Leucite Hills, that named from its native state "Wyomingite," gives fifty-seven per cent.
If he looks up the word in the Unabridged that he carries in his satchel he will find that leucite is a kind of lava and that it contains potash.
Crystal of augite with banded walls, and indented by leucite crystals, from the lava of 1794.
Group of leucite crystals of irregular form from the lava of 1855, congregated around a nucleus of crystals of plagioclase and magnetite.
Crystals of leucite with microliths and cavities darkened by magnetite dust; also, containing crystals of magnetite.
In the lava of Vesuvius leuciteis an essential, and perhaps the most abundant mineral.
The view of Professor Judd, that leucite easily changes into felspar, and that some ancient igneous rocks which now contain felspar were originally leucitic, does not seem to be borne out by the above facts.
The lava of Vesuvius may be regarded as a variety of basalt in which leucite replaces plagioclase, although this latter mineral is also present.
Section of leucitecrystal from the lava of 1868, with fluid cavities.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "leucite" in a variety of sentences. We hope that you will now be able to make sentences using this word.
