So You Think You've Found A Meteorite....
Such is possible, but many 'meteorites' reported to the Dutch Meteor Society turn out to be either natural stones or Man-made products like iron furnace slags. Sometimes, it can be very difficult to tell genuine meteorites from industrial waste products (especially in the case of alledged 'iron meteorites') and even professional geologists can be fooled by pseudo-meteorites sometimes!
If you indeed think you've found a meteorite, the checklist below can be helpfull. If you have gone through this checklist and still think it is a meteorite, then either contact a research institute (like a Natural History Museum or the Geology department of a University) or fill in the report form accompanying this page. But note that usually things will turn out disappointing: meteorites are rare and chances of finding one are small. But certainly not impossible! Since every new genuine meteorite can, by means of scientific research, have a large contribution to scientific knowledge, reporting suspected 'meteorites' is very worthwhile. No two meteorites, even those from the most common L6 class, are completely alike, and every new meteorite contains new clues to meteorite formation and the history of the early solar system. So don't be afraid to report: it can be of large importance if your 'object' indeed turns out to be a meteorite! And if it is not: well, maybe you are more succesfull a next time. Though the chances of actually encountering one are small, there must be several meteorites out there on the fields waiting to be picked up. For the Netherlands for example, it is estimated that on average each year a 100 grams specimen impacts somewhere in the country, and each 3 years a 1 kg specimen should impact somewhere in the Dutch meadows. Yet, since 1840 only 4 (four!) specimens have been recovered in the country (Utrecht 1840, Uden 1843, Ellemeet 1925 and Glanerbrug 1990), in all cases because either someone had been eyewitness to the impact or (like the Glanerbrug meteorite, 1990) because it caused damage to a building during impact. Undoubtedly, many Dutch meteorites directly fell into eternity and are lost forever.
A check-list for possible meteorites
Meteorites come into three major types, which are in theirselves divided into several subtypes:
- Stony meteorites
- Iron meteorites
- Stony-iron meteorites
The differences in composition between and therefore texture of different types and even subtypes of meteorites can be large, so it is impossible to give an overall description of 'the' typical meteorite. Still, there are some overall characteristics you should check first.
The magnetic test. The fast majority of meteorites is magnetic, i.e. like metal (and to be exact: because they contain metal (stony meteorites too!)) they atract a magnet. So the first thing you should do is tying a small but strong magnet to a string and slowly bring it close to your 'meteorite'. If it is a meteorite, it should be atracted. Note that the atraction of a stony meteorite is usualy too weak to be discernable with a hand-held magnet, and this is the reason why you should ty it to a string: even the smallest attraction will become discernable with that method by a movement of the magnet.
Weight. Because they either contain metal (like stony meteorites) or are almost entirely composed of metal (like iron meteorites), meteorites are 'heavy'. If possible, you should weigh it and try to estimate the density of the material in grams per cubic centimeter. Stony meteorites have densities of 3.6 grams/cm^2 (2.2 grams/cm^2 in the case of the very rare carbonaceous chondrites), Iron Meteorites have densities of 7.9 grams/cm^2 and Stony-iron meteorites have densities of 4.9 grams/cm^2. Most natural stones have densities <3.0 grams/cm^2.
Fusion crust visible? 'Fresh' fallen meteorites show a
fusion crust of molten material. Usually this crust is very thin, in the order of
one millimeter or less. It has a dull black or dark grey and in rare cases
brownish or glassy appearance, while after some time 'in the field' it can
become rusty brown due to corrosion (since meteorites contain metal, they
severely rust when exposed to the terrestrial environment for some time).
The exterior of a meteorite (the parts containing a fusion crust) can (but do
not always) show 'remaglyphts' or 'thumb-prints': small shallow depressions
like vingerprints pressed in a piece of clay. They are caused by the ablation
proces when the meteorite passed through the atmosphere. Sometimes, small
specks of shiny molten metal and distinct flow lines can be seen.
It should be emphasised that many natural terrestrial rocks and industrial
waste products show corrosion and weathering crusts that can be strikingly
similar to a 'fusion crust' and remaglyphts at a first glance.
Shape. Meteorites are usually smoothly rounded, with distinct rounded corners, but never neatly globular. So called 'oriented' meteorites can be cone-shaped. Sharp edges do usually not occur, unless the stone has broken up after atmospheric passage.
Internal texture
This element deserves some special attention. The first thing to be remarked
is: never shatter a possible meteorite to pieces with a hammer
or by employing a saw!!!! In such a way, you can forever
destroy scientificly valuable material. In addition, never experiment with acids,
cleaning solvents, glues or varnishes for the very same reason!
If you do want to have a look at the interior (and such can be necesarry for a
better judgement of the genuinity of the piece) and your specimen seems
completely fusion crust covered, it is better to employ, with some carefulness,
the 'Nininger test'. Take an electric sand stone used for sharpening knives and
other metal tools. Gently press a little corner of your specimen on the polishing
stone, just a second or so, to remove a thin and small layer from the
'meteorite' in order to expose a small piece of the interior. Only some square
millimeters are needed, no more.
If your specimen is a meteorite, you should see either polished metal, compact stone, a mixture of shiny metal and compact stone or in rare cases yellowgreen cubic cristals with rounded corners in a matrix of shiny metal. Vesicles, bubbles or cavities should not be present:
The Dutch Meteor Society each year receives many would-be 'meteorites' which are porous: they contain vesicles, cavities and bubbles in their interior. With a true meteorite, this can never be the case! So when your supposed 'meteorite' is porous, I must disappoint you: it can not be a genuine meteorite... A porous object can not survive the stresses imposed on it during passage through the atmosphere and due to it's porousity has a very large ablational surface: it would violently annihilate long before it could reach the Earth's surface. Meteorites, though they can be brittle in some rare cases, always are very, very compact. This is an important thing to consider. The many porous objects which we receive each year usually turn out to be industrial slag material or basaltic volcanic stones. These are widely used for soil hardening, road and railroad construction, building construction etcetera. The country is literally littered with them. In addition, iron furnace slags and basaltic grinding stones from medieval or even prehistoric times frequently turn up. And they are frequently mistaken for 'meteorites' by lay persons. The argument that 'natural stones do not occur at this location, so it must be a meteorite' almost never goes, just because of the fact that human actions both nowadays and in (pre-) history distributed materials to many places, how remote they might be. So be not surprised to find volcanic stones when there is no volcanic outcrop for hundreds of miles around....
Some additional notes on meteorite interiors
Stony meteorites have a compact texture, are usually rough at cracked surfaces, like natural igneous rocks. Their colour is usualy light grey, but can be almost white, dark grey, brownish or black too. Sometimes, dark clasts appear in a lighter matrix, i.e. a brecciated appearance. Chondrites, one of the subtypes of stony meteorites (and the most frequent type of meteorite) contain small millimeter sized rounded silicate inclusions called chondrules. L-type and H-type chondrites contain nickel-iron specks which are easily visible as small shiny particles when turning your specimen in the light. Some meteorites contain golden-yellow crystals of troilite, which is an iron sulfide which looks like pyrite. Rust staining can occur after only a few days of exposure to a terrestrial environment.
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The famous Ensisheim meteorite, on exhibit in Ensisheim, France. It fell in AD 1492, and it is the second oldest surviving meteorite of which the fall has been witnessed (Photograph by P. Jenniskens, DMS). |
Iron meteorites are black, 'rusty' or very dark grey when unpolished. When polished, they have a bright shiny metal colour, due to the fact that they are almost entirely composed of an alliage of nickel and metallic iron.
Stony-iron meteorites, which are rare by the way, come in two different forms. One, the so called Pallasites are often regarded the most beautifull of all meteorites. They consist of green or yellowish-green, cubish crystals of the mineral Olivine, usually with rounded corners, in a matrix of bright nickel-iron metal (when polished). Mesosiderites consist of a chaotic mix of chunks of bright nickel-iron and chunks of silicate ('stony') material.
Some notes on alledged 'meteorite falls'
Many objects DMS gets for scrutiny are reported to have 'fallen from the sky' and sometimes reportedly hit persons. Still, they were not meteorites... By some mysterious force, many man-made materials seem to 'fall' from the sky. We have had iron furnace slags 'impacting', volcanic tephrites (in a non-volcanic area!) smashing windows, a yellow-painted lead object (which seriously injured someone), a piece of World War II shell (hitting a woman on the head at the thirth floor of an appartement building in 1988), pieces of ice smashing roofs in the middle of the summer and more of such strange phenomena. Explanations could be vandalism, young boys with catapults, crossing airplanes losing clumps of ice or even parts of their machinery, strong winds blowing of roofing material, and in some cases I even suspect birds! In other cases, people might simply be mistaken.
To put it short: not everything that seems to 'fall' is a meteorite! But, of
course, when you notice a stone to 'fall', it is worth paying attention to because
there is a good chance that it is a meteorite indeed.
Note that meteorites impact with very high velocities of about 200 meters/second:
the velocity of an artillery shell! This means that they cause impact pits,
serious damage to trees, cars and buildings, and serious if not deadly injuries
when they should hit someone. If you notice such damage, make a detailed
description and try to make photographs and measurements (for example of
diameters and depths of impact pits). And don't forget to call a doctor when
someone is hurt... Note that from about 10 km altitude, incoming meteorites
have lost their cosmic speeds and are falling more or less perpendicular. Any
horizontal movement is due to winddrift, not to entry direction. To close these
notes: meteorites are not red hot when they reach Earth
surface, contrary to what many people think. They will not
burn or scorch vegetation or materials, they will not burn your hands when you
pick them up.
