1248 
Muscovite flakes also occur as alteration products of nepheline. 
Larger crystals of aegirine show distinctly a higher augite content 
in their central part the needles often show a sheaf-shaped or radial 
arrangement. 
Sölvsbergites. 
Under this name we have grouped the rocks in which probably 
felspathoids occurred, but in smaller quantity than in the tinguaites. 
The felspathoids cannot be recognised any more as such, the second- 
ary minerals, however, are indicative of their having been present 
originally. Then the rocks approach the tinguaites. 
ype 1 (with pyrowene). lt is distinguished from the above-mentioned 
tinguaite by the dark grey colour of the finely crystalline ground- 
mass, against which numerous white or light-red phenocrysts, which 
no doubt consist for the greater part of felspar, are sharply outlined, 
while also a few larger pyroxene crystals occur. It was collected 
from a dyke between the Serra de Cabucu and the Serra de Marapicu. 
Orthoclase is the predominant mineral of the phenocrysts; in 
small quantity polysynthetically twinned felspars occur with small 
extinction-angles. More or less regularly defined groups, consisting — 
chiefly of acid plagioclase and cancrinite, sometimes mixed with 
analcite, possibly point to original felspathoids. Beside larger crystals 
of aegirine-augite with a high augite-content, which decreases in 
zonary crystals in a narrow marginal zone, also a few phenocrysts 
of brown amphibole and very little biotite occur together with larger 
_ ore-crystals. The groundmass consists of numerous pyroxene-needles 
sometimes of zonary structure and consisting of aegirine and aegirine- 
augite. Sometimes the central part of zonary crystals is of a violet 
colour with a great extinction-angle indicating the presence of titani- 
ferous augite, which was also observed in some large crystals. Very 
few amphibole prisms occur. In the colourless mass between them 
felspar can be recognised, originally it probably consisted chiefly of 
felspar and felspathoids; at present there is an abundance of cancrinite 
and analcite as products of alteration. Inclosures of ore are numerous. 
Type 2 (with amphibole). It was collected near type 1 also from 
a dyke. It is a dark grey fine-crystalline rock with some felspar- 
phenocrysts. Original felspathoids are not noticeable, but the cancrinite- 
content of the groundmass points to their former existence. True 
amphibolephenocrysts do not occur, though we do see accumulations 
of brown-green amphibole and ore which sometimes show a regular 
outline. 
The groundmass is composed of a good many plagioclase-laths 
which are sometimes polysynthetically twinned, of markedly pleo- 
