Lavas Bearing Leucite.--The lavas are the most abundant of the igneous rocks bearing leucite. They include leucite trachytes and phonolites, and leucitophyres, leucite basanites and tephrites, leucite basalts and leucitites.
The leucite trachytes and phonolites carry sanidine in abun dance; they are common in the vicinity of Rome (L. Bracciano, L. Bolsena) and in the tuffs in the region of Naples, and occur in north-west Madagascar (Bezavona mass), the Celebes and Alaska.
In the leucitophyres sanidine is in subordinate amount, these rocks being the effusive equivalents of the leucite syenites. They often contain much nepheline, which is typically absent in the leucite phonolites. Haiiyne, nosean, melanite and aegirine also occur. Leucitophyres are known from various parts of the vol canic districts of the Rhine (Eifel, Kaiserstuhl), and from S5.o Paulo, Brazil, where they are of Carboniferous age.
The leucite basanites and tephrites are basaltic lavas carrying leucite, plagioclase and augite, the former with olivine, the latter olivine-free. Leucite is often present in two sets of crystals, por phyritic and as a constituent of the ground mass. The pyroxene is usually titaniferous and aegirine is uncommon. Accessory min erals include biotite, brown hornblende and haiiyne. Melanite and nepheline may also occur. The leucite basalts and leucitites are free from plagioclase felspar. The former contain olivine and the latter are olivine-free. Otherwise they resemble the basanites and tephrites. Melilite may be an abundant constituent, as in the leucitite of Capo di Bove, near Rome. In this rock the melilite forms irregular tetragonal plates enclosing many small rounded crystals of leucite. The volcanic region of central Italy provides the finest and best known examples of basaltic lavas carrying leucite. In the Roman region leucite tephrites and leucitites occur in the Alban hills, south of Rome, and in southern Etruria, north of Rome, at Lake Bracciano, Viterbo and Lake Bolsena. In the
Neapolitan area these rocks are represented at Roccamonfina, Monte Vulture, Phlegrean Fields (and Islands) and at Vesuvius. Leucite basanites also occur in these districts. The tephrites and basanites are also known from Sardinia, Czechoslovakia, in East Africa, at Kilimanjaro, and other places, in the Celebes and Java. Leucitites occur also in the East Indies, Montana, and the Kim berley district of Western Australia. In East Africa they are the products of the volcanoes Wissoke, Mikeno, Niragongo, etc., and of the volcano Etinde in the Cameroons. The more basic leucite basalts rich in olivine occur in great force in the Eifel, in Czecho slovakia, and accompany tephrites or leucitites in the Celebes, Java, Montana and Sardinia. Leucite basalt occurs at the Gauss berg (Antarctica) and in the western plains of New South Wales. A small group of leucite-bearing rocks is recorded from the Philippines, and from Utsuryot6, in the Sea of Japan, a variety of leucite tephrite has been recently described. Peculiar leucitic lavas of lamprophyric affinities occur in the Leucite hills of Wyoming and at Jumilla, Murcia Province (Spain). The Wyoming lavas carry phlogopite, diopside and katophorite, with or without sani dine felspar, and constitute the rocks known as orendite and wyomingite.
As a constituent of pyroclastic rocks, leucite is abundant in the ashes and tuffs known as "peperino" in the Roman region ; this is externally quarried for building and paving purposes.
2. Leucite tinguaite, Magnet Cove, Ark.
4. Leucitite, Capo di Bove, Rome.
5. Leucite basalt, El Capitan, New South Wales.
6. Leucite tephrite, Gillinan river, Mt. Mouriah, Java.
7. Orendite, North Table Butte, Wyoming. (C. E. T.)