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 and meteorite identification to help you get started on finding out for sure. Like the old saying a picture is worth a thousand words. The meteorite photographs here and elsewhere on the internet should be of assistance in determining if it is a meteorite or meteor-wrong.
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. For our purpose here let us work with the three main families.
All meteorites regardless of type make a dangerous passage through the atmosphere before arriving on the ground. During this passage they are shaped by the heating and melting so that they often receive flight markings called regmaglyphs. These pits in the surface have also been called thumbprints for they resemble the depressions an artist might make in clay with fingers. Because of them meteorites are different in appearance from normal terrestrial rock. Some meteoroids pass through the atmosphere in such a stable way that only one surface is mainly heated and melted. In these meteorites the thumbprints may form a radial pattern and the melted material may roll over from the incoming surface onto the backside. There it cools as a raised bump around the perimeter of the back edge. There may be fine lines of melted material on the surface also. These type of meteorites are referred to as being oriented and though they are quite rare they are for even the beginner the easiest to recognize just from their outward appearance.
Several features are noteworthy in this photograph. First, the thumbprints or regmaglyphs acquired during flight through the atmosphere. Second, the black fusion crust is very nice. Thirdly, the spots of brown coloring caused by the rusting of metal grains. The weathering will continue as the stone is exposed to more rain and ultimately the black color will be gone.
This is by far the largest of the three main groups. These meteorites look like a rock since they are made of mostly mineral material. But, true meteorites are usually much heavier for their size than an Earth rock. Making ‘Heavy for Size’ the first thing to examine in your suspect rock.
If the rock has a broken edge it will be solid inside. It will not be porous like lava rocks often 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. The chondrules may be difficult to see unless you grind a spot with a diamond file. But, the stone 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 terrestrial rocks 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 it is a good indication that you may 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.
The slab of meteorite shown above is of a low petrological type chondrite. What this means is the chondrules seen are distinct, sharp edged features and there is little blurring from melting and recrystallization. Three of the dozens of visible chondrules have been circled for recognition. Often chondrules along with the metal grains will be visible in a hand lens while hunting if a spot on the stone is ground off flat.
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. However, many rocks on the Earth that are not meteorites contain iron minerals and these are magnet responsive also. Magnetite is one of the most common magnetic minerals and is often found in rocks. It will stick to magnets. But, it will not show metal grains when ground off 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 while it is 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 hunting the rocks.
The meteorite shown here is somewhat older then the one pictured above. There is more brown staining. The brown spots are thicker and more crusty in appearance. A few cracks have begun to appear from freeze and thaw cycles but overall the stone is still fairly solid.
This stone has no remaining black fusion crust, it shows a surface that is beginning to be mechanically eroded by sand blasting and continuing freeze and thaw fracturing. The cracking from this is more evident then in the previous photograph.
At this point in the weathering process the meteorite above begins to look more like a terrestrial rock. It has not remaining fusion crust but has acquired a desert varnish coating. It is seriously cracked. In fact, many smaller fragments from this mass have likely already separated to be recovered independently. The surface is fully sandblasted. A meteorite in this state has likely been on the Earth for thousands of years.
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. There is no metal 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 or looks like it has flight markings, send it to be examined.
Much more rare to find are meteorites made almost entirely of nickel-iron. Though this type is what we often see in museums, irons account for only a small percentage of the number of total meteorites recovered. 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 metallic. If you file or grind on them they will show bright metal like any piece of iron from your garage or a junkyard that is rusted on the outside.
Above are shown two nicely sculptured pieces of Canyon Diablo meteorite iron. Their shapes are a combination of the way they were torn from the main mass, and the activity of weathering. Iron meteorites have the tendency to exfoliate layers of material from their surface as time passes on Earth. In meteorites like Canyon Diablo with 50,000 years of exposure to Earth’s environment this is the major reason for their current shape. These have been moderately cleaned. When found there would usually be a layer of orange-brown crust covering 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, car parts, motorcycle parts all of which 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 not for the first time rock finder. 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. Twenty grams of a meteorite or 20% of a small meteorite is donated to fulfill the requirement for official registry. This amount will be placed in a permanent collection for scientists to have access to after the analysis is complete.
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 and harder than a steel file. 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. 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, since it often has a residue of iron along with the melted rock component. But furnace slag is often porous and meteorites are not.
Externally stony-iron meteorites will resemble iron meteorite. But, closer examination will often reveal the presence of olivine crystals scattered on the outside amongst the metal. This photo is of an acid etched slice of a pallasite. The metal is surrounding the olivine crystals which are generally highly fractured.
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 per year that turns out to be a real meteorite. Good luck.
Stone meteorites are cut by the testing facility into slices so thin that the minerals in the rock become transparent. Upon examination under a microscope the chondrules of the stone can be studied. The characteristics of the meteorite seen under the microscope are a portion of the information used to determine the classification of stone meteorites. Today however, information from very specialized electronic equipment is also vital in making an exact classification. No stone meteorite is officially classified any longer on optical microscopy alone. But, such observations are usefully in determining of a rock is a meteorite or not before further work is done. The photo above shows many chondrules of various types.
Stone meteorites are cut by the testing facility into slices so thin that the minerals in the rock become transparent. Upon examination under a microscope the chondrules of the stone can be studied. The characteristics of the meteorite seen under the microscope are a portion of the information used to determine the classification of stone meteorites. Today however, information from very specialized electronic equipment is also vital in making an exact classification. No stone meteorite is officially classified any longer on optical microscopy alone. But, such observations are usefully in determining of a rock is a meteorite or not before further work is done. The photo above shows many chondrules of various types