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
		Minute Chondrules	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.