METEORITE OR METEORWRONG?
basalt
Basalt and related rock types like andesite and
dacite are rocks that form when volcanoes erupt magma (lava) onto the
surface of the earth and the magma cools.
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Basalt flows in Hawaii.
Click on image for enlargement.
(photos by Randy Korotev)
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Basalts come in a wide variety of textures and
colors. Some have vesicles (gas bubbles),
some don't. Some are gray, others are reddish or even greenish. Basalt
is one of the most common rock types on Earth. Except for the coral,
all of the rocks of Hawaii are basalts. Much of Oregon and Idaho is
covered with basalt.
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Closeup of a piece
of fresh basalt from Hawaii. Sometimes the glassy surface of
a fresh basalt
is mistaken for a meteorite fusion crust.
This basalt rock does not have the rounded, aerodynamic shape of
a meteorite and it contains far too many vesicles for
a meteorite. Click on image for enlargement.
(photo by Randy Korotev) |
Basaltic volcanism occured on other terrestrial
planets, too. Venus, Mars, the Moon, and some of the largest asteroids
had volcanoes that produced basalt. Eucrites are basaltic meteorites
from the asteroid belt. About 17% of the Moon is covered with basalt
and about 14% of the lunar meteorites are
basalts. (See "How Do We
Know It's a Rock From the Moon?") Most of the Martian
meteorites are basalts (all of those known as shergottites). All
basalts, regardless of where they were formed, are similar because
the process that formed them (melting in the interior of a planet)
is the same. Unfortunately, the only way to distinguish
a terrestrial (Earth) basalt from a basaltic meteorite (Moon, Mars,
asteroid) is with expensive chemical and mineralogical tests. If you
find a basalt, it's probably not a meteorite.
"lava rocks"
The handful of rocks below came out of a bag sold at a garden
shop. They are intended to be used in landscaping or in barbeque grills,
where they help distribute the heat evenly. All are vesicular
basalts.
See also meteorwrongs 016 |
018 | 038 |
044 | 068 |
079 | 112 |
137 | 141 |
161 | 208 |209
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