meteorites

Meteorites

peak crater
Defintions
Where Do Meteorites Come From?
How Did Meteorites Get from Asteroids to the Earth?
Origins of Particular Meteorite Types
How Old Are Meteorites?
Meteorite Classification Table
How to Preserve Meteorites
Summary Meteorite Finds and Falls
Common Meteorite Minerals (separate file)
How to Identify Meteorites (separate file)
Meteorite Cratering on Earth(separate file)




 

Meteorite (n): A mass of stone or metal that has reached the earth from outer space.

Meteor (n): A transient fiery streak in the sky produced by a meteoroid passing through the earth's atmosphere.

Meteoroid (n): A small body traveling through space.

Where Do Meteorites Come From?

Since there are many kinds of meteorites, they may come from different extraterrestrial objects Here are a few things scientists study to determine the source of meteorites:
 

They compare them to rocks collected on the Moon and observed by space craft on Mars. A few meteorites resemble these rocks.
They observe the orientation of crystals in meteorites to determine if they solidified in a strong gravitational field. Strong gravity will result in more oriented crystals. This has allowed scientists to infer that some very rare types of meteorites come from Mars--apparently blasted off the surface of that planet by a meteorite impact.
They analyze the light reflected from meteorites--a fancy analysis of color--and compare it to light reflected from meteorite specimens found on Earth. This has allowed scientists to determine that the most likely source for most meteorites is the Asteroid Belt between Jupiter and Mars.

How Did Meteorites Get from Asteroids to the Earth?

The short answer--one that we hope to explain better as this page is developed--is that Asteroids bump into each other. Pieces break off or the orbit may be changed. Asteroids can only stay in certain orbits. Once their course is deflected, the gravity of the planet Jupiter can fling asteroids or fragments out of the Asteroid Belt and into an orbit that crosses the orbit of the Earth. Once this happens, there is a chance of collision--and a chance of a meteorite hitting the Earth.
Chondrules--the First Rocks
Scientists have hypothesized that the first solid matter was dust--tiny mineral grains that solidified from the gases that proceeded them at the beginning of the universe. The dust clumped together. Perhaps electrical charges or gravitational attraction made this happen. The clumps melted. We are uncertain of the reasons for the melting. Heat from star systems may have caused it--or radioactivity in the clumps themselves. (Billions of years ago, matter was far more radioactive. Because of their age meteorites are among the least radioactive rocks known.) When the clumps melted, small spheres were formed. These are chondrules.

 

Origins of Particular Meteorite Types

Chondrite Parents
Chondrules floating in space eventually clumped together again, this time with other chondrules and the cosmic dust. The result was chondrite parent bodies--we know them as asteroids or planets.

Iron and Stony Iron Meteorite Parents
The clumping together of the larger material, like the initial clumping, had the effect of concentrating the radio activity and resulting heat. Parts of the rock melted. The heavier material--metallic iron and nickel settled by gravity to the center of the forming mini-planet. This is the parent for iron meteorites. Outside of the iron, a mixture of iron and other minerals formed the parents of stony-iron meteorites. The process is called differentiation.

Achondrite Parents
By the theory, the melting and differentiation would also result in lighter rocks. These would be like the lava we see emerging from volcanoes on Earth. They would form the parents for achondrites

 

How Old Are Meteorites?

If meteorites formed from dust from the early universe, then we would expect them to be very old. Indeed, this is what we find. Scientists have used radiometric dating to measure the ages of meteorites. The results show ages of around 4,500,000,000 years--about seven hundred million years older than the oldest rocks on Earth.

 
 


Meteorite Classification Table
Catagory Compostion Type Distinguishing Features Letter Designation



Chondrule Character
Chondrites 
Stony Meteorites are characterized by chondrules --small spheres (average diameter= 1 mm) of formerly melted minerals that have come together with other mineral matter to form a solid rock. Chondrites are believed to be among the oldest rocks in the solar system. 85.7 percent of meteorite falls are chondrites.
Enstatite Chondrite Distinct E4
Less Distinct E5
Indistinct E6
Melted E7
Ordinary Chondrite

The most common meteorite from observed falls. 

High Iron (12 to 21% metallic iron ) (also called Bronzite Chondrites)  Abundant H3
Distinct H4
Less Distinct H5
Indistinct H6
Melted H7
Low Iron (5 to 10% metallic iron ) (also called Hypersthene Chondrites) Abundant L3
Distinct L4
Less Distinct L5
Indistinct L6
Melted L7
Low Metal Content (about 2% metallic iron ) (also called Amphoterites) Principle minerals are bronzite , olivine , and minor oligoclase . Abundant LL3
Distinct LL4
Less Distinct LL5
Indistinct LL6
Melted LL7
Carbonaceous Chondrite

 These rare meteorites contain elemental carbon , a basic building block for life.

Friable, more water Absent CI
Friable, less water  Sparse CM2
Iron-rich olivine , Calcium Aluminum Inclusions Sparse CV2
Abundant CV3
Distinct CV4
Less Distinct CV5
Minute Chondrules Abundant CO3
Distinct CO4



Characterisic Minerals
Achondrites 
Stony Meteorites without chondrules. Scientists believe that some of these meteorites originated on the surface of the Moon or Mars. . 7.1 percent of meteorite falls are achondrites.
Aubrites Enstatite AUB
Angrite Augite ACANOM
Ureilites Olivine - pigeonite AURE
Subgroup HED Howardites Eucrite-diogenite mix AHOW
Eucrites Anorthite - pigeonite AEUC
Diogenites Hypersthene ADIO
Subgroup SNC Shergottites Basaltic AEUC
Nakhlites Diopside - olivine ACANOM
Chassignite Olivine ACANOM



Widmanstaaten Bandwidth
Irons (structural classification)
These meteorites are made of a crystalline iron-nickel alloy . Scientists believe that they resemble the outer core of the Earth. Widmanstatten bands are a crystal form. 5.7 percent of meteorite falls are irons.
Hexahedrites >50mm H
Octahedrites Coarsest 3.3-50mm Ogg
Coarse 1.3-3.3mm Og
Medium .5-1.3mm Om
Fine 0.2-0.5mm Of
Finest <0.2mm Off
Plessitic <0.2mm ( Kamacite spindles) Opl
Ataxites (no structure) D


Minerals Structural Classes
Irons (Chemical Classification)
A second scheme for classifying iron meteorites is by their chemistry. The determining factors are groupings of meteorites with similar ratios of trace elements to nickel. Generally, the higher the Roman numeral of the classification, the lower the concentration of trace elements. The casual observer cannot see this as one can with the Widmanstatten bandwidth that is the determining factor for structural classification. Chemical classification is important because it suggests that certain iron meteorites share a common origin or were formed under similar conditions. 
kamacite , taenite , silicates , carbides Om-Og I
kamacite , taenite , silicates , carbides Om-Og-Anom. I-Anom
kamacite , daubreelite H IIA
kamacite , taenite Ogg IIB
kamacite , taenite Opl IIC
kamacite , taenite Of-Om IID
kamacite , taenite , troilite Om-Og IIIA
kamacite , taenite , phosphides Om IIIB
kamacite , taenite , carbides Of IIIC
kamacite , taenite , carbides Off-D IIID
kamacite , taenite , cohenite , graphite Og IIIE
kamacite , taenite Of IVA
kamacite , taenite D IVB
kamacite , taenite , silicates , graphite All Anom



Primary Minerals
Stony Irons 
These meteorites are mixtures of iron-nickel alloy and non-metallic mineral matter. Scientists believe that they are like the material that would be found where the Earth's core meets the mantle.  1.5 percent of meteorite falls are stony irons.
Pallasites iron , olivine PAL
Mesosiderites iron , Ca pyroxene , plagioclase MES
Lodranites iron , pyroxene , olivine LOD
Siderophyre iron , orthopyroxene IVA-ANOM




How to Preserve Meteorites

Space is dry and that is how you should keep your meteorites. Remember that no matter where you live there is moisture in the air. Your meteorites are especially likely to absorb that moisture if they contain chloride (salt) or change temperature. Changes in temperature can cause condensation like that you will find on a cold can of soda. When salt cakes, it is drawing moisture out of the air. If your meteorite has any salt in it it will draw moisture out of the air. Moisture and salt can damage a meteorite very quickly.

To protect your meteorites you should do the following:

Keep your Meteorites Dry
Here is a list of things that you can do to keep your meteorites dry: Use Cleaning and Coating to Protect Your Specimens
Irons
Any iron that is left out is likely to be handled--you should assume by sweaty hands. For this reason, you need to clean your specimen periodically. I recommend that you use anhydrous alcohol.
The next step is to coat the specimen. I coat natural irons with Rust Guardit, a spray on wax coating. Some people use Sheath which is a petroleum distillate like WD40. I have used WD40 as well, but I don't prefer it because they add water to it

For etched irons, heat the specimen to 200º F (95º C) and apply "Rig" grease. After the specimen cools, wipe off the excess grease.
Stones
If a stony meteorite is susceptible to rust, my policy is to keep it dry. I keep it in a box with desiccant. If any stone is handled much, it is a good idea to clean it with alcohol. I do not use any coating on stones as I believe that coatings interfere with observation of the natural features.
 

Repairing Meteorites
If you collect meteorites, it is inevitable that some specimens will be damaged or deteriorate. Most often the damage can be repaired and further damaged can be stopped or slowed. Damage to most specimens can be related to two things: Rust and chloride (salt). Rust is the symptom, chloride is the disease. Both need to be removed.
Removing Rust
Most often rust can be removed with a little elbow grease and a steel wire brush. Use anhydrous (or 95%) alcohol to do your washing. Alternatively, you can use a petroleum distillate rust 'remover'. Sheath or WD40 are examples. On etched surfaces or bare metal surfaces that have lots of cracks, you might want to try phosphoric acid. Naval Jelly is one brand of phosphoric acid rust remover. After you use the acid, be sure to clean it all off using alcohol or distilled water. Etched irons will have to be re-polished and etched.
Removing Chloride
Here is a process recommended by Steve Schoner (American Meteorite Survey,ams000@aztec.asu.edu):
The real problem with rusting in meteorites is chlorine. Rinsing the meteorite with water, (tap water) should never be done if any of these treatments is used. For some reason, meteorite irons have an affinity for chlorine, and it is chlorine that is the main cause of rusting.
Often it comes to the surface of cut or wire brushed irons as little dark brown or green blebs of fluid.
What this is is FeCl2, FeCl3, or even NiCl2, or NiCl3 (in much smaller amounts).
Ferric and Ferrous Chloride (FeCl2 & FeCl3) are hydroscopic substances, that is they have an affinity for moisture just as a desiccant does.
Then once the water is present and these are in solution, the Chlorine is free to bond to other iron atoms attacking it so that it will combine with oxygen, producing iron oxide. Once a thick coat of rust develops, then the "bleeding" stops and the meteorite becomes more or less stable. Some though, will continue to rust till they actually fall apart.
At one time the iron and nickel chlorides in meteorites were described as "Lawrenceite" after the mineralogist that first identified it. It was thought at the the the time that they were present in the meteorite before it fell to earth, but it was later found that it was a substance that formed in the meteorite from reactions between terrestrial groundwater and salts.
The trick to stop this rusting is to get rid of the chlorine. Fortunately, a good long soak in alcohol will dissolve iron-nickel chlorides, but I have found a much better way.
Soak the affected specimen in a strong solution of distilled water 50%; isopropyl alcohol 30%, and sodium hydroxide (lye) 20%. The percentages are by weight.
When mixing the sodium hydroxide crystals in this solution be very careful as it gets hot. Also it is caustic, and if gets on the skin will burn just as badly as if it were an acid.
Use stainless steel containers.
Put the meteorite in the solution and let it soak for a few days to a week. If the solution gets tainted so that it looks rusty then you might want to replace the solution sooner than a week. Pour out the solution, and clean the surface of you meteorite. This solution is strong enough to strip most irons of their varnish coatings, but I recommend that it is done beforehand. You will notice after this first soak that there are big blobs of gelatinous rust on the iron surface. Some of these will be green but most will be dark brown. This is Fe0H and nigh, both are like jelly in water but when exposed to air expel their hydrogen and become solid iron an nickel oxides.
The chlorine that caused the rusting is now in the solution as NaCl, (salt) having exchanged places with the iron atoms in the meteorite for the Na (sodium) in the caustic solution. Chlorine has a greater attraction for sodium than iron, so that is why this solution works better than just keeping air and moisture away from the meteorite.
Get rid of the chlorine, and you get rid of the problem.
I stumbled upon this process over 20 years ago, and have used it with great success to treat some of the most stubborn rusting meteorites in my collection, including Brenham and more recently Lamont, which is a mesosiderite. Lamont is a very unusual olivine rich meteorite, maybe a link between the Lodranites and the mesosiderites, but unfortunately it is a prolific ruster. Soaking my 900 gram end piece six times over six weeks has seemed to cure it, as it is now on my shelf with no varnish coating and not a speck of rust on its cut surface.
With pallasites, the crystals tend to pop out. But if you are very, very patient, and like puzzles, you can clean the places where they were, then re-insert them with super-glue. Then after everything is together re-finish the surface so that it looks good as new.
Iron meteorites will, however have to be re-polished, and etched. And be sure to use only distilled water so as not to re-infect your meteorite with chlorine which is the primary cause of the progressive rusting of our specimens in the first place.
This solution can also be used in electrolysis-- a much more aggressive method of removing chlorine from iron. This is done for the preservation of iron artifacts that are recovered from shipwrecks. It is more involved and it does work.


 
 

Meteorite Finds and Falls before 1972
Chondrites
Letter 
Designation
Falls 
Number
Falls 
Kg
Finds 
Number
Finds 
Kg
Total 
Number
Total 
Kg
Percent 
Falls
E3 1 4 Kg 0 0 Kg 1 1 Kg 100%
E4 2 142 Kg 3 1 Kg 5 143 Kg 80%
E5 2 28 Kg 0 0 Kg 2 28 Kg 100%
E6 6 52 Kg 2 7 Kg 8 59 Kg 75%
Total
Enstatite
Chondrites
11 226 Kg 5 8 Kg 16 234 Kg 69%
H3 4 40 Kg 5 309 Kg 9 349 Kg 44%
H4 16 985 Kg 21 266 Kg 37 1251 Kg 43%
H5 53 1057 Kg 23 210 Kg 76 1267 Kg 70%
H6 30 486 Kg 14 871 Kg 44 11357 Kg 68%
H? 121 869 Kg 163 1305 Kg 284 2174 Kg 43%
Total
Bronzite
Chondrites
224 3437 Kg 226 2961 Kg 450 6398 Kg 50%
L3 8 71 Kg 2 60 Kg 10 131 Kg 80%
L4 11 719 Kg 10 478 Kg 21 1197 Kg 52%
L5 23 862 Kg 21 494 Kg 44 1356 Kg 52%
L6 107 3118 Kg 48 1555 Kg 155 4673 Kg 69%
L? 107 854 Kg 124 1299 Kg 231 2153 Kg 46%
Total
Hypersthene
Chondrites
256 5624 Kg 205 3886 Kg 461 9510 Kg 56%
LL3 5 90 Kg 0 0 Kg 5 90 Kg 100%
LL4 1 80 Kg 1 44 Kg 2 124 Kg 50%
LL5 7 181 Kg 2 3 Kg 9 184 Kg 78%
LL6 16 669 Kg 4 46 Kg 20 715 Kg 80%
LL? 20 9 Kg 8 123 Kg 28 602 Kg 71%
Total
Amphoterites
49 1499 Kg 15 216 Kg 64 1715 Kg 77%
Carbonaceous
Chondrites
33 2543 Kg 3 34 Kg 36 2577 Kg 92%
Anomalous
Chondrites
1 1 Kg 2 26 Kg 3 27 Kg 33%
Total All
Chondrites
574 13330 Kg 456 7131 Kg 1030 20461 Kg 56%
Achondrites
Name 
Designation
Falls 
Number
Falls 
Kg
Finds 
Number
Finds 
Kg
Total 
Number
Total 
Kg
Percent 
Falls
Aubrites 8 1200 Kg 1 5 Kg 9 1205 Kg 89%
Diogenites 8 68 Kg 0 0 Kg 8 68 Kg 100%
Ureilites 3 5 Kg 3 4 Kg 6 9 Kg 50%
Howardites 17 34 Kg 2 7 Kg 19 41 Kg 89%
Eucrites 20 207 Kg 3 24 Kg 23 231 Kg 87%
Anomalous
Achondrites
4 51 Kg 1 1 Kg 5 52 Kg 80%
Total
Achondrites
60 1565 Kg 10 41 Kg 70 1606 Kg 86%
Irons
Chemical 
Classification
Falls 
Number
Falls 
Kg
Finds 
Number
Finds 
Kg
Total 
Number
Total 
Kg
Percent 
Falls
I 5 188 Kg 64 94500 Kg 69 94688 Kg 7%
I-Anom 2 107 Kg 17 7450 Kg 19 7557 Kg 11%
IIA 4 304 Kg 39 3259 Kg 43 3563 Kg 9%
IIB 1 23000 Kg 13 5089 Kg 14 28089 Kg 7%
IIC 0 0 Kg 7 201 Kg 7 201 Kg 0%
IID 2 66 Kg 9 1100 Kg 11 1166 Kg 18%
IIIA 4 32 Kg 113 100846 Kg 117 100878 Kg 3%
IIIB 1 63 Kg 39 28045 Kg 40 28108 Kg 3%
IIIC 1 1 Kg 5 144 Kg 6 145 Kg 17%
IIID 0 0 Kg 5 54 Kg 5 54 Kg 0%
IIIE 0 0 Kg 7 705 Kg 7 705 Kg 0%
IVA 1 4 Kg 38 22250 Kg 39 22254 Kg 3%
IVB 0 0 Kg 11 60487 Kg 11 60487 Kg 0%
Anomalous
Irons
4 46 Kg 88 74396 Kg 92 74442 Kg 4%
Irons
type?
7 87 Kg 45 32200 Kg 52 32287 Kg 13%
Total
Irons
32 23898 Kg 500 430726 Kg 532 454624 Kg 6%
Stony Irons
Name 
Designation
Falls 
Number
Falls 
Kg
Finds 
Number
Finds 
Kg
Total 
Number
Total 
Kg
Percent 
Falls
Pallasites 2 45 Kg 31 7162 Kg 33 7207 Kg 6%
Mesosiderites 6 479 Kg 14 1153 Kg 20 1632 Kg 3%
Anomalous
Stony Irons
1 1 Kg 5 224 Kg 6 225 Kg 17%
Total
Stony
Irons
9 525 Kg 50 8539 Kg 59 9064 Kg 15%
Many numbers in this table are estimates and others are dated.

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