Meteorite Information Page
The following will try to give a tangible, yet brief explanation of many things meteoritic. This is a new section in our web site and it is currently under construction. The field of meteoritics is quite vast and there are many excellent books and videos available from many outstanding researchers and authors. I will start with a brief explanation of the different kinds of meteorites. Following that you will find a few definitions that I will present that should help the reader to understand the information presented on meteorites in these pages. Italicized words indicate that they are explained in our dictionary section, which will continue to grow as time allows.. We hope to have plenty of thumbnail images to help give the visual element to our explanations. If there please just click on the image to see if we have attached a link to get a larger picture on your screen. When studying meteorites please bear in mind that this is a science that is still defining itself and new discoveries often occur which do not always seem to fit into the simplified classification schemes that are in use today. Only through continued study will this system be refined and, hopefully, lead us to a better understanding of this little corner of the universe we call home. Please contact us with any suggestions as to how we can improve this page or make it easier to navigate and take in.
What are Meteorites?
Meteorites are remnants of the material that formed our solar system and have survived the trip through our atmosphere to arrive on the surface of our planet. Approximately four and a half billion years ago the material that was to build our solar system came into being. The first of the elements that we know on the periodic table of elements formed in the core of a star that existed here before our sun came into being. Then when that star went super nova the remaining heavier elements were formed. Over time many these individual grains began to bump into one and other forming ever larger masses. This process continued until much of the material was in the form of larger asteroidal or planetary bodies.... many of which still survive today... such as this little chunk of rock we call home. Over time many of these objects collided as can be seen by the abundant impact craters on our neighboring planets and moons, not to mention the growing number of identifiable craters on our planet as well. They are harder to see on the earth due to the vigorous geologic processes that continually modify the surface of the planet but there are plenty crater structures still recognizable. Many of these impacts led to shattered planetoids which in turn increase the amount of material drifting around to make new craters on any world that happens to get in its way. Over the past ~4.5 billion years most of the debris has been cleared out by the orbiting planets and their moons however there is a great deal of debris in between the orbits of Venus and Jupiter. It is thought that this debris may be the remains of a failed planet or it could just be material enough for a planet that cannot form due to the disruptive gravitational pull from Jupiter. Beyond the orbit of Pluto there is another area that is known to contain a great deal of unincorporated debris. This is called the "Oort cloud" and is where comets are thought to originate from. When the objects in either of these belt areas are affected by collisions or the affects of gravitational forces their orbit may be altered enough to send them traveling through the inner solar system. Meteorites are very important to science in that by examining them we are able to (in many cases) view the very stuff that came to be our solar system. All the rock on earth (while starting out as the same material as meteorites) has been reprocessed by the active geological forces here to the point that it has no resemblance to the original material. At the end of 1999 there were 22,507 known meteorites. All meteorite names must be approved by the Meteoritical Society and names will reflect the nearest geographical location to the find or fall.. if at all possible. If the exact location is not known they will be assigned a regional name and a number indicating the order in which it was found in the particular area. Examples of this would be the NWA (Northwest Africa) meteorites from Morocco and Algeria or the Sahara meteorites from the desert regions of Libya and Egypt.
Types of Meteorites
In the simplest break down there are three types of meteorites: STONE, IRON and STONY IRONS.
Stones: Is pretty self explanatory, they consist almost entirely of stony mineral components. This would be chondrules and the dust of crushed chondrules and any other solar (or rarely interstellar) mineral grains that happen to have been in the area when all the material combined to form the parent asteroid or planetoid or meteoroid. Also commonly found in stone chondrites are small grains of "metal" which are a mineral of iron and nickel (Fe Ì Ni). Testing for the nickel is one of the main ways that meteorites are confirmed to actually be meteorites. While most of the meteorites in this class are called "common or ordinary chondrites" and are further broken down in to "L" (low iron) chondrites, "H" (high iron) chondrites and "LL" (low iron metal & low total iron) amphoterites. There are several, less common, types of chondrites such as "C" (carbonaceous) chondrites, "R" (Rumarutiites) chondrites and "E" (enstatites) chondrites. In addition to this there are a small percentage of stony meteorites that are quite unusual. For more information (and many images) on the various types of chondrites please look in the "Glossary of Terms" section below. These are called "Achondrites" since the chondrules are no longer visible due to their having formed from a melt. There are numerous classes of Achondrites and we will try to get them listed in these pages as soon as we can. These have undergone great change since their formation and where at some point incorporated into a larger "parent body" such as a planet, moon or larger asteroid. While on these parent bodies they were subject to varying degrees of heating and compression either from radioactive decay of the elements, deep burial or impacts or any combination of these events. These meteorites are highly prized by scientists and collectors as they give clues into the geologic processes that have affected the other planets and moons (and large asteroids) in our solar system. A rare few of the meteorites recovered have been identified as having originated on the Moon or the planet Mars.
Irons: The iron meteorites are formed on parent bodies that undergo enough heating to cause the iron grains to melt and migrate to the center because of gravity. This is the same way that our earth got its core, which is also made up of iron-nickel. The iron meteorites are "liberated" when there is some sort of catastrophic event, most likely collisions with other parent bodies, which exposes the iron core to space. It subsequently cools and may become a large iron asteroid like we have seen in the movies or it could be in the form of many smaller "chunks" that could be future meteors or meteorites. The irons are divided into 3 main types: hexahedrites less than 6% Ni), octahedrites, which are the most common (6- 16% Ni), and ataxites (more than 16% Ni). The differences being in the amount of nickel and other volatiles present. When the octahedrites are polished and etched with acid they reveal what the internal crystal structure looks like as the widmanstatten patterns become visible.
Stony-irons: As the name implies these are made up of a combination of iron and stony material. The stony irons seem to be the remains of many violent events which occurred early on during the formation of our solar system. They appear to have formed during collisions of large objects that caused melting or the upwelling of molten material. This would explain the metal (Fe-Ni) being intermixed with such a wide variety of other lithologies that you would not normally find with molten metal. The stony irons consist of various sub-types such as mesosoderites, pallasites, silicated irons.
Glossary of Terms
Ablation: As an object enters our atmosphere it experiences extreme heating to its surfaces which in turn causes a portion of the object to melt or be vaporized. This loss of material is called "ablation".
Acapulcoite: This class of meteorites are very rare and represent a class of primitive achondrites that have experienced a moderate degree of melting and recrystalization. Lots of visible metal grains as well.
Accretion: The process by which dust, individual grains, and chondrules are accumulated through contact with other objects in space leading to the formation of meteoroids, asteroids and planetoids.
Achondrite: Is a meteorite in which chondrules are not visible. These have undergone extensive change due to re-melting of the original chondritic material from the heat of radioactive decay, burial or impacts or any combination these events. That being the case means that this class of meteorites are formed from the complete melting or partial melting of the original chondritic material. If any of the rocks from our planet were to make it into space to become meteoroids this is the class they would fall into. The following is a list of the different classes of achondrites, for more detailed information on each class please read below. The 14 classes are: Acapulcoite, Angrites, Aubrites, Brachinites, Diogenites, Eucrites, Howardites, Lodranites, Lunar, SNC (Martian), Ureilites, Winonaites, Ungrouped and Unclassified. The image below is a cumulate eucrite (Dhofar 007)
Amphoterite: Refers to the "LL" class of meteorites. Please go to the "LL chondrite" definition below for more information.
Angrite: These meteorites indicate that they crystallized from a melt of basaltic composition. Their formation ages are also very old at ~4.56 billion years. This age means that they were formed in the very early stages of the formation of our solar system.
Anhedral: Refers to mineral grains that do not have clearly defined crystal faces.
Armored chondrule: This is the term used to describe a chondrule that is entirely ringed (encircled) in metalic iron. The image below is of an easily discernible armored chondrule from the Gold Basin, Arizona L4.
Asteroid: A large body of stone or iron (or both) that is not in orbit around a particular planet or moon.
Asteroid belt: The debris filled area between Mars and Jupiter containing enough material to make up one or more planets. This is where most of the meteoritic material that reaches the earth is believed to originate.
Astrobleme: This term is basically referring to a large crater structure except that it is very ancient and may be almost indistinguishable on the surface. Often it takes a closer examination of the rocks in and around the structure to see if they exibit any signs of the high shock that would be associated with a large impact event.
Ataxite: Class of iron meteorite with no widmanstatten pattern and they consist of more than 16% nickel.
Aubrite: Are also melt created and contain large crystals of enstatite. The aubrites are almost always brecciated and have a close association with the enstatite chondrites. It is believed that they formed in the same inner part of the solar system as well.
Basalt: This is volcanic rock that has flowed to the surface. This is generally very f