Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 2 - By Alexander Von Humboldt And Aime Bonpland.


































































































































 -  He discovered that each crystal
of pyroxene, enveloped in the earthy mass, is separated from it by
fissures parallel to - Page 121
Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 2 - By Alexander Von Humboldt And Aime Bonpland. - Page 121 of 777 - First - Home

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He Discovered That Each Crystal Of Pyroxene, Enveloped In The Earthy Mass, Is Separated From It By Fissures Parallel To The Sides Of The Crystal.

These fissures seem to be the effect of a contraction which the mass or basis of the mandelstein has undergone.

I sometimes saw these balls of mandelstein arranged in strata, and separated from each other by beds of grunstein of ten or fourteen inches thick; sometimes (and this situation is most common) the balls of mandelstein, two or three feet in diameter, are found in heaps, and form little mounts with rounded summits, like spheroidal basalt. The clay which separates these amygdaloid concretions arises from the decomposition of their crust. They acquire by the contact of the air a very thin coating of yellow ochre.

South-west of the village of Parapara rises the little Cerro de Flores, which is discerned from afar in the steppes. Almost at its foot, and in the midst of the mandelstein tract we have just been describing, a porphyritic phonolite, a mass of compact feldspar of a greenish grey, or mountain-green, containing long crystals of vitreous feldspar, appears exposed. It is the real porphyrschiefer of Werner; and it would be difficult to distinguish, in a collection of stones, the phonolite of Parapara from that of Bilin, in Bohemia. It does not, however, here form rocks in grotesque shapes, but little hills covered with tabular blocks, large plates extremely sonorous, translucid on the edges, and wounding the hands when broken.

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