The Wayback Machine - https://web.archive.org/web/20110902013218/http://meteorites.wustl.edu:80/realities.htm
| Checklist |
Examples |
Caveats
& Comments |
| The chance of finding a meteorite is exceedingly small. |
|
Most rocks are not meteorites. |
| The chance of finding a meteorite that has just fallen
is even smaller. |
|
Since 1900, the numbers of recognized meteorite "falls"
is about 690 for the whole Earth. That's 6.3 per year. Only
98 of those occurred in the US. That's less than 1 per year. |
| Not everything that falls from the sky is a meteorite. |
|
Read some stories. |
| Not every rock that looks like a meteorite is a meteorite. |
|
It is often not possible to determine whether a rock is a meteorite
just from its appearance. |
| Some meteorites don't look like meteorites. |
|
If someone had walked into my office with this rock, I'd have
said that it probably wasn't a meteorite. |
| If it does not have a fusion crust,
then it's probably not a meteorite. |
|
Some meteorites do not have obvious fusion crusts,
but that's rare. Usually there's fusion crust on at least one face. |
| If it does have some kind of rind or coating,
the rind or coating is probably not a fusion crust and the rock isn't a
meteorite. |
|
There are numerous processes on Earth that cause rocks
to have coatings and rinds. Some of these, particularly desert
varnish, can look remarkably like a meteorite fusion crust. |
| If it's got a thick rind or coating, then
it's not a meteorite. |
|
Fusion crusts are thin because as soon as the exterior
of the meteoroid melts, the liquid is sloughed off because of the high velocity
of the meteoroid. When the meteoroid slows down, there's not enough heat
to cause melting. |
| If the inside is the same color as the outside, it's probably
not a meteorite, |
|
Fusion crusts are usually darker than the interior of a meteorite. |
| If it "looks burned," it's probably not
a meteorite. |
|
Meteors don't burn. Meteorites aren't burned. The outside has
melted, but they aren't burned. |
| If it's a big rock, then it's probably not a meteorite.
|
|
Most stony meteorites are smaller
that people think they are. But, occasionally, someone finds a really
big one. |
| If it's big and it does not have
regmaglypts, then it's probably not a meteorite. |
|
Not all meteorites have regmaglypts, however, but
the big ones usually do. |
| If it's angular, with sharp edges or points and no
smooth sides, then it's probably not a meteorite. |
|
For small meteoroids, 90% of the mass
is lost to ablation as it come through the atmosphere. Edges and "corners"
are the first parts to ablate away. Put and ice cube in water an wait for
90% to melt. The "cube" that's left will have no edges or points.
It's like that with meteorites. |
| If it's stony (not an iron) and has a rough exterior,
then it's probably not a meteorite. |
|
| If it's stony (not iron) and has sharp protuberances, then it's
probably not a meteorite. |
|
| If it's square, rectangular, or has flat sides, then it's probably
not a meteorite. |
|
| If it has veins, swirls, foliation, radiating features,
or tubes, then it's not a meteorite. |
|
Rarely, there might be veins of impact melt (see
NWA 482). Some meteorites have veins of metal.
|
| If it's got layers, lamination, or any kind of linear
or planar features, then it's definitely not a meteorite. |
|
Layered rocks occur on Earth because the Earth has
gravity. Most meteorites come from objects (asteroids) too small to have
any appreciable gravity. If there is no gravity, then there is no way to
form layers.
Here is the only
exception I know about, and it's a terrestrial weathering effect. |
| If it contains elongated minerals or clasts, then
it's probably not a meteorite. |
|
Among meteorites of which I'm aware, MIL 05035 (an
unbrecciated basalt) has the most elongated minerals; see photomicrograph.
It is exceedingly rare for the aspect ratio of a clast in a brecciated meteorite
to exceed 3-to-1. |
| If it's spherical or circular, then it's probably
not a meteorite. |
|
There are processes on Earth that lead to spherical
rocks (spheroidal weathering, tumbling and abrasion in water). These processes
don't occur where most meteorites come from. |
| If it contains round things, they're not necessarily chondrules. |
|
Lots of earth rocks contain round things. |
| If it's got lots of holes in it, then it's not a meteorite.
|
|
Very few stony meteorites have vesicles or holes.
In those that do, the holes are sparse and small (Do a Google search for
photos of Ibitira
and Dhofar
081.) Vesicles require gas. There's not much gas where most meteorites
come from. Iron meteorites often have holes, however. |
| If it contains amygdules or rounded clasts, then it's
probably not a meteorite. |
|
|
| If rock or mineral grains stand out from the matrix
or have been plucked out leaving a cavity, then it's probably not a meteorite.
|
|
In many terrestrial sedimentary rocks, the clasts
are harder than the matrix. Sometimes they pop out of the rock. That doesn't
happen in meteorites. |
| If you found it on the beach, then it's probably not
a meteorite. |
|
I aware of only one
meteorite that was found on a beach. |
| If you found it in a stream bed, along a river, or
any other place where there are lots of rocks, then it's probably not a
meteorite. |
|
Successful meteorite hunters search for meteorites
in places where there ARE NOT a lot of rocks. If you want to find your car
easily, park it in an empty parking lot. |
| If you found it near a road or railroad track, then
it's probably not a meteorite. |
|
It may have fallen off a train or truck. |
| If it contains quartz, then it's not a meteorite. |
|
Quartz is the only common mineral that will easily
scratch glass. Try to scratch glass with a
sharp edge of the rock. If it makes a deep scratch, its not a meteorite.
|
| If the rock is "really hard," then it's probably not
a meteorite. |
|
Because meteorites don't contain quartz (the hardest common terrestrial
mineral), they're not all that hard. |
| If it consists of hematite or magnetite, then it's
probably not a meteorite. |
|
Highly weathered meteorites may contain hematite,
magnetite, and maghemite. |
| If it 's glassy and vesicular, then it's not a meteorite. |
|
It's probably a piece of slag. |
| If it's made of metal or looks metallic, then it might
be a meteorite, but it's probably not. |
|
Human-made stuff like slags are often mistaken for
meteorites. Slags typically contain some glass and have vesicles (gas bubbles) |
| If the rock contains shiny things that look like metal,
but the rock is not magnetic, then the shiny things probably aren't metal
and the rocks isn't a meteorite. |
Some sulfide and oxide minerals look like metal. |
| If it attracts a magnet but does not contain obvious
metal, then either it's not a meteorite or it's a highly weathered meteorite. |
|
Meteorites are magnetic because they contain iron
metal. Earth rocks don't contain iron metal. Many Earth rocks are magnetic
because they contain magnetite, however. |
| If it does not attract a magnet, then it
could still be a meteorite, but it is probably not. |
Many of the rarest types of meteorites are not magnetic,
but then neither are most Earth rocks. |
| If it's "heavy for it's size," then it might
be a meteorite, but it's probably not. |
|
The commonest kind of meteorites, the
ordinary chondrites, contain iron
metal; that makes them denser than most Earth rocks. However, some Earth
rocks are dense like meteorites. To confuse the issue, some rare meteorites
have low densities like common Earth rocks. |
| If it's not heavy for it's size, then it
might be meteorite, but it's probably not. |
| If it's reddish, particularly on the inside, then
it's probably not a meteorite. |
|
Most meteorites are shades of grays and browns; some
may be reddish on the outside. |
| If it's got polygonal or columnar jointing, then it's
not a meteorite. |
|
|
| If it's stony (not iron) and has a really goofy shape,
then it's probably not a meteorite. |
|
|
| If it's hollow, then it's not a meteorite. |
|
|
| If it does not look like other rocks in the vicinity,
then it might be a meteorite, but it's probably not. |
|
|
| If there's writing or a picture on it, then it's not
a meteorite. |
|
|
| If it's in a conspicuous place, then it's probably
not a meteorite |
|
|
| If it's radioactive, then it's not a meteorite. |
|
Only the thorium-rich lunar meteorites like SaU 169
are slightly radioactive when tested with a Geiger counter. |
| Many-to-most rocks sold over the Internet as meteorites really
are meteorites; some are not. |
|
They're are many reputable meteorite dealers that sell real meteorites
on the Internet. I've bought several meteorite specimens from such dealers.
However, there are foolish or devious people who try to sell backyard rocks
as meteorites. Most rocks offered on e-bay for prices >$10,000 are not
really meteorites. Sometimes, cheap meteorwrongs
are offered for sale, however. |
| Advertisements for alleged meteorites that are filled
with meaningless, pseudoscientific mumbo-jumbo and absurdly high prices
are usually selling just rocks. |
|
Some people just don't have enough real work to do. |
| If you find a real meteorite, it probably isn't worth
as much ($) as you think or wish. |
|
|
| Meteorological is not the same as meteoritical. |
|
|
