Nature
The glass is light to dark green, white or black. The glass takes the form of twisted masses, fragments or chunks up to 10 cm. Internally it has a flowing texture defined by lines of elliptical bubbles. There are two kinds of Darwin glass when composition is measured. Type 1 is normally white or green whereas type 2 is normally black to dark green. The dark glass contains less silica and more magnesium and iron than the light green glass. The dark glass is also enriched in chromium, nickel and cobalt. A possible explanation for the chemical differences is that, in addition to being mainly composed of melted local metamorphic rocks, the type 2 glass also contains a component of extraterrestrial material from the meteorite. Darwin glass has been dated at about 816,000 years old using argon dating methods.
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Famous quotes containing the word nature:
“I am a leader by default, only because nature does not allow a vacuum.”
—Desmond Tutu (b. 1931)
“The wildest dreams of wild men, even, are not the less true, though they may not recommend themselves to the sense which is most common among Englishmen and Americans to-day. It is not every truth that recommends itself to the common sense. Nature has a place for the wild clematis as well as for the cabbage. Some expressions of truth are reminiscent,—others merely sensible, as the phrase is,—others prophetic.”
—Henry David Thoreau (1817–1862)
“When Nature was shaping him, clay was not granted
For making so full-sized a man as she wanted,
So, to fill out her model, a little she spared
From some finer-grained stuff for a woman prepared,
And she could not have hit a more excellent plan
For making him fully and perfectly man.”
—James Russell Lowell (1819–1891)