K20 10.17 d 
—— = <== Subrang: de bepacnose: 
Na?O 0.05 1 
Although the analysis points to a rather high percentage of quartz 
the SiO? percentage is rather low fora rhyolite, it approaches already 
more that of trachytes. With regard to this fact and taking into 
consideration the high percentage of Fe’O*, the specifie weight is 
very high for a rhyolite namely 2.623. 
It cannot be said that there is a similarity of any significance 
between the real mineralogical composition and the one calculated 
from the analysis. For this too few individuals have separated from 
the magma. So we discover under the microscope only a very slight 
quantity of more or less rectangular sanidine-plates, besides very few 
lath-shaped plagioclases, and likewise very rarely some augite-crystals. 
The groundmass is amorphous, chiefly microfelsitic. On the spots where 
it has become crystalline no distinguishable constituents occur. Occa- 
sionally spherulitic formations are detected. It is however very rich 
in ore-particles, by far the greater quantity of these should be classed 
with hematite, though they are only exceptionally plate-shaped. As 
a rule one discerns only black and irregularly shaped particles, and 
it is these that accumulate in the “Schlieren” and make them appear 
black at first sight. Besides this difference which has already come 
off at the differentiation of the magma the main mass of the rock 
does not vary in the least from the “Sehlieren”. B. KALKowsky when 
examining the genuine piperno which in a mineralogical and che- 
mical respect differs so much from the rock originating from the 
Pelapis Islands, had already come to the same result.) 
“Wer könnte aa der Lavennatur des sonderbaren Piperno zweifeln?” 
onee exclaimed Lror. von Been.*) He was mistaken, for at all events 
during the last decenniums objections have been made against this 
view. Besides A. Scaccut*), Luvier DELL’ Ersa*), P. Franco ®), especially 
1 Ueber den Piperno. Zeitschr. d. Deutschen geolog. Gesellsch. XXX. Berlin 
1878, p. 673. 
2) Geognost. Beobachtungen auf Reisen. Il. Berlin 1809, p. 209, reprinted in 
Gesammelte Werke I. Berlin 1867, blz. 459. 
3) This was still his opinion in 1849. Afterwards he regarded the piperno as a 
metamorphosed volcanic conglomerate (A. Scaccui. La regione vulcanica fluorifera 
della Gampania. Alti Acc. Sc. fis.e. Mat. (2) IL. Napoli 1828, No. 2 p. 103). 
tj Considerazioni sulla genesi del Piperno. Atti Accad. Sc. fis. e Mat. (2) V. Napoli 
1893, N°. 3. [1891] p. 1—22, reprinted in Giornale di Mineralog'a, Cristallografia e 
Petrografia Ill. Milano 1892, p. 23—54. 
5) Il piperno. Boll. Soc. Naturalisti. Napoli 1901, p. 34—52 (Geol. Centralbl. 
VII. Berlin 1905—6, p. 98). 
