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also occur. They consist of muscovite flakes; whether the original 
mineral has partially belonged to felspathoids, which the form some- 
times seems to suggest, could not be made out with certainty. In 
the groundmass the same felspars occur, the laths contain more of 
the strongest double-refracting felspar mentioned above, this felspar 
sometimes exhibits polysynthetie twins and occurs also in a few 
separate crystals. The groundmass contains also muscovite, calcite, 
rather much apatite and ore, which occurs also in some larger 
erystals, is strongly weathered and consists partly of pyrite. 
Type 2. Near the facenda D. Eugenia a rock was collected with 
white to faintly reddish coloured felsparphenoerysts in a light-gray, 
finely crystalline groundmass. The rock is strongly sericitised, although 
the felsparphenocrysts have been altered very little. Initially it may 
have contained felspathoids. Ore, leucoxene and titanite occur. 
Nephelinesyeniteaplites. 
These rocks are known only as boulders near Mount Sapé in 
the Serra di Marapucu (western part of the Serra di Gericino). 
Macroscopirally it presents itself as a medium-, to fine-grained light- 
grey rock, with numerous black points chiefly consisting of magnetite. 
The constituents are: clear albite, less clear orthoclase and micro- 
perthite, nepheline and analcite, magnetite and little pyrite, titanite 
apatite and green or brownish biotite. 
The nepheline is often enclosed by the felspars. The albite reveals 
itself in a large quantity in polysynthetically twinned crystals. There 
is an abundance of analcite; a Cl-reaction with a negative result 
points to the absence of sodalite. 
Tinguaites. 
Typical tinguaites were collected near Maxambomba, the rocks 
seem to form a dyke here and also a flow, the latter of a thickness 
of more than 100 meters. Only a single sample was examined, most 
likely several varieties and also typical effusive rocks occur here. 
The sample contains in a grey finely-crystalline groundmass a 
few phenocrysts of light-coloured felspar, consisting of Na-bearing 
orthoclase or anorthoclase. They have been partially converted into 
natrolite. Microscopically the groundmass seems to consists of felspar 
laths aegirine, natrolite, analcite and a little nepheline. Some prisms 
with high refractive indices and strong birefringence, which show 
parallel extinction and are optically positive, point to zircon. 
The colourless substance with low refractive index which exists 
in large quantity between the felspar laths, is probably chiefly 
composed of analcite, which is partially an alteration product of 
original nepheline. 
