( 548 ) 
Under the microscope the rock is seen to consist of felspar, nepheline, 
less sodalite, much aegirine, (aegirine augite) and titanite and small 
quantities of apatite, fluorine, calcite, analcime, and titanic iron ore. 
The felspars are orthoclase and mieroperthite in Carlsbad twins. 
Nearly always nepheline and sodalite are transformed, respectively 
into pseudomorphoses of mica and zeolites. In the crystals of nepheline, 
which are not entirely transformed into mica, the transformation begins 
along the fissures, but nearly all the crystals are entirely altered. 
The sodalite pseudomorphoses consist of zeolites, in which we find 
distributed some small flakes of mica. 
The aegirine is strongly pleoehroic from olive-green to yellowish 
green, some crystals are homogeneous, other ones contain a centre 
of aegirine augite, which has for the greater part very low extinction 
angles; they are very rich in inclusions of small crystals of titanite 
and apatite, and they are strongly impregnated with fluorspar. 
The titanite forms the well known twins after (001), in the 
rhombic sections the long diagonal is the twinning plane; both 
individuals are polysynthetically twinned. They are pleoehroic from 
salmon coloured to colourless. 
The apatite is the first product of crystallization, it is even formed 
as small idiomorphie inclusions in the titanite, for the greater part 
the crystallization of the other elements was simultaneous; the aegirine 
is idiomorphie in relation to felspars and felspatoids but in general the 
contactlines are irregular and show simultaneous crystallization. The 
felspar includes some idiomorphie crystals of nepheline and sodalite, 
mainly it is the latest product of crystallization. Probably in pneuraa- 
tolytical way, fluorine, calcite, and analcime crystallized in the remaining 
cavities. 
Ii is evident how much the mineralogical composition of this rock 
differs from that of the normal types of nepheline syenite by its 
high content of aegirine and titanite. A. Lacroix x ) gave the name 
of cavite to the mesocratic form of this group and of teralite to the 
melanocratic form; as the type of covite he considers the rock of 
Magnet Cove in Arkansas, described by Washington and as type 
of teralite the alkali felspar-nepheline rocks from the Crazy Moun¬ 
tains in Montana. 
The chemical composition of the rock here described is shown 
in I of the following table (analysed by F. Pisani) ; it is compared 
with the analyses of some eovites and teralites. 
i) Materiaux pour la Mineralogie de Madagascar. Extr. nouv. Arch, du Museum. 
4c serie, Tome 1, pag. 184. 
