Do you think you
have found a meteorite? You have been to the desert or river or perhaps even
your backyard and found a rock that is unusual. You think that it might be a
meteorite. Here is some simple information about meteorites to help you get
started on finding out for sure.
Meteorites come in three different large families. But, to be honest there
are a lot more actual types within the three families so it can be
complicated to make a refined classification. But for our purpose here let's
work with the three main families.
Stone
Meteorites - This is by far the largest of the three main types. These
meteorites look like a rock since they are made of mostly mineral material
similar to many rocks originating here on Earth. But, true meteorites are
often much heavier for their size than an Earth rock. So 'Heavy for Size'
is the first thing to examine in your suspect rock.
If the rock is broken it will be solid inside. It will not be porous like
lava rocks are. It may have small round structures like tiny balls showing
on the broken surface. These are called chondrules and many stone meteorites
(the chondrites) will have them. But it will not have holes inside if it is
a meteorite. Most stone meteorites will not have shiny crystals in them.
They will not be layered or banded with different strips of mineral types.
So 'Solid' and 'Not Crystalline' and 'Not layered' are
phrases to remember.
Stone
meteorites often have grains of nickel-iron in them. Metallic iron in rocks
from the Earth is very rare. The moist atmosphere of the Earth has turned
almost all native iron to some other chemical form of iron long ago. So, if
you grind off a small spot on your suspect rock and find bright shiny metal
spots this is another good indication that you might have a meteorite of the
stone type. One thing to think about here is what I mean by shiny metal
spots. These will not be a metallic luster or shininess. The metal spots in
meteorites will be actual metal; they will look the way the chrome on a car
looks. So having 'Metal Grains' is the next thing on our list of
characteristics.
Because meteorites often have iron metal in them they will respond when a
strong magnet is brought near them. If a magnet will stick to your rock or a
magnet will pull the rock when it is hung from a string that may mean there
is iron metal in the suspect rock. You will want to grind a little spot as
discussed above and see if there is metal. But many rocks on the Earth that
are not meteorites contain iron in chemical forms that are magnet
responsive. Magnetite is one of the most common and is often found in rocks.
It will stick to magnets. But, it will not have metal grains when ground and
the powder produced by the grinding will be black. The powder produced by
grinding most meteorites will be brown. Fresh meteorites may not make brown
powder but older stone meteorites usually will. So 'Responds to a Magnet'
and makes a 'Brown Streak or Powder' is the next characteristic.
Meteorites pass through the atmosphere of the Earth initially at the speed
they had in space. This speed is thousands of miles per hour. They interact
with the thin air high above the ground and are melted on the outside
surface. This melted coating is called 'Fusion Crust'. It is often
black if the meteorite is freshly fallen, but will turn more and more brown
as time passes laying on the ground. The iron grains and minerals will rust
and weather making the meteorite browner. So 'Black or Brown on the
Outside' is the feature we are now discussing but it maybe the first
thing to look for in the rocks.
If your rock has these characteristics there is a chance that it is a
meteorite. You will want to find a meteorite expert to look at it. At the
end of this article is a list of laboratories and testing facilities that
specialize in meteorite analysis.
If your rock had some of the characteristics but not all it is still
possible that it is a type of stone meteorite. Some stone meteorite do not
have much metal or any metal so there is none to see when you grind them and
they will not respond to a magnet very much. You will have only their
external appearance to go by. If you think it is fusion crusted and looks
like it has flight marking from traveling through the atmosphere while
melting on the outside, send it to be examined.
Iron Meteorites - Much more rare to find are meteorites made almost
entirely of nickel-iron. These meteorites will be black or brown on the
outside. They will be very heavy and a magnet will stick strongly to them
since they are metal. If you file or grind on them they will show metal like
any piece of iron from your garage or a junkyard that is rusted.
Iron meteorite and meteorites in general can be almost any shape. They will
have smoothed off rounded corners, but do not have to be spherical in shape.
Iron meteorite and other type may be marked on the outside surface by
depressions. These are commonly call thumbprints. I use this name instead of
the scientific term "regmaglyphs" since thumbprints describes them pretty
well. Imagine pushing your thumb many times into potter's clay. This is the
kind of marks meteorites have sometimes on their exterior surface. Remember
they are not porous. They will not have holes, but they may have these
depressions on the surface.
Iron meteorites can easily be confused with rusted pieces of manmade iron
and steel. Old mill balls and cannon balls become good imitators of
meteorites after many years of rusting. The same is true for airplane parts
and car parts, motorcycle parts all are found in the desert and other
isolated areas now. Testing for the presence of nickel is often required to
determine for sure if a chunk of iron is meteoritic. All iron meteorites
have nickel along with the iron. This test is complicated enough to make it
something that probably is not for the first time rock finder. But send the
rock to a testing facility for analysis. Or if you can remove a piece send
that instead. A piece the size of a walnut will be plenty for a
determination to be made. If it is a meteorite that much should also satisfy
the requirement for official classification and inclusion in the Catalogue
of Meteorites. The finder is required to submit a finder's report to the
Meteoritical Society whose online address can be found below. Twenty grams
of a meteorite or 20% of a small meteorite is donated to fulfill the
requirement. This amount will be placed in a permanent collection for
scientists to have access to after the analysis is complete.
Stony-Iron Meteorites - These are the last main type of meteorite. As
the name indicates they have characteristics of both the previous types.
They are made of a mixture of nickel-iron and stone. It will be possible to
file or grind and find abundant metal. But it will often be possible to find
spots on the surface where a regular file is useless since the material is
mineral. The mineral portion can be dark silicate minerals or it can be
yellowish green or yellowish brown olivine crystals. Stony-iron meteorites
will be heavy since they contain a lot of iron. They will often be very
rusted for the same reason. And the olivine crystals may have discolored on
the outside or fallen out from weathering and rusting processes. Furnace
slag is sometimes confused for stony-iron meteorite material, since it often
has a residue of iron along with the melted rock component. But furnace slag
is often porous and meteorites are not.
Testing facilities are used to receiving rocks that are not meteorites. They
get hundreds even thousands a year. Don't hesitate to send your rock or a
portion of it away if it meets some or all of these guidelines. You might
have one of the handful a year that turns out to be a real meteorite. They
are there working and wanting to find them at the laboratory or university.
Good luck.
Do you
still think you
have found a meteorite?
The web pages below will help you find all the information you need to determine if you have a meteorite or a
meteorwrong.
Continue on to these pages to master your
meteorite identification skills.
