Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 1 - By Alexander Von Humboldt And Aime Bonpland.
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We Are Surprised
To See An Atlantic Nation Substituting, Like The Natives Of
America, Vitrified Lava For Iron.
In both countries this variety of
lava was employed as an object of ornament:
And the inhabitants of
Quito made beautiful looking-glasses with an obsidian divided into
parallel laminae.
There are three varieties of obsidian at the Peak. Some form
enormous blocks, several toises long, and often of a spheroidal
shape. We might suppose that they had been thrown out in a softened
state, and had afterwards been subject to a rotary motion. They
contain a quantity of vitreous feldspar, of a snow-white colour,
and the most brilliant pearly lustre. These obsidians are,
nevertheless, but little transparent on the edges; they are almost
opaque, of a brownish black, and of an imperfect conchoidal
fracture. They pass into pitch-stone; and we may consider them as
porphyries with a basis of obsidian. The second variety is found in
fragments much less considerable. It is in general of a greenish
black, sometimes of murky grey, very seldom of a perfect black,
like the obsidian of Hecla and Mexico. Its fracture is perfectly
conchoidal, and it is extremely transparent on the edges. I have
found in it neither amphibole nor pyroxene, but some small white
points, which seem to be feldspar. None of the obsidians of the
Peak appear in those grey masses of pearl or lavender-blue,
striped, and in separate wedge-formed pieces, like the obsidian of
Quito, Mexico, and Lipari, and which resemble the fibrous plates of
the crystalites of our glass-houses, on which Sir James Hall, Dr.
Thompson, and M. de Bellevue, have published some curious
observations.* (* The name crystalites has been given to the
crystalized thin plates observed in glass cooling slowly.
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