Types of Meteorites

Classification of Meteorites
Category				Designation
Stony Meteorites	Composition Type		Chondrules
Chondrites 82% of meteorite falls Chondrites are stony meteorites that are characterized by the presence of chondrules. Chondrules are millimeter-sized spherical minerals that appear to be melted aggregregates, however their mechanism of formation has yet to be determined. Chondrites are believed to be the most primitive and among the oldest rocks in the solar system. Designations for alteration levels of chondrites: Chondrites experienced varied degrees of aqueous/metamorphic alteration most clearly reflected by the chondrules within meteorite matrix. A number is assign between 1 and 7 to designate the level and type of alteration. A designation of "3" indicates unaltered chondrules. Numbers greater than 3 indicate increasing thermal metamorphism of the chondrules. Numbers less than three indicate increasing aqueous alteration of the chondrules. A designation of 1 or 7 indicates that chondrules have been obliterated by alteration.	Ordinary Chondrites 73.5% of falls Designations: H L LL Some meteorites are classified as transitional between the main groups, e.g., H/L, L/LL	H Chondrites 31.4% of falls High Iron (12-21% metallic iron) also called Bronzite Chondrites.	Abundant	H3-H3.9
			Distinct	H4
			Less Distinct	H5
			Indistinct	H6
			Melted	H7
		L Chondrites 34.8% of falls Low Iron (5-10% metallic iron) also called Hypersthene Chondrites.	Abundant	L3-L3.9
			Distinct	L4
			Less Distinct	L5
			Indistinct	L6
			Melted	L7
		LL Chondrites 7.2% of falls Low Metal Content (2% metallic iron) also called Amphoterites.	Abundant	LL3-LL3.9
			Distinct	LL4
			Less Distinct	LL5
			Indistinct	LL6
			Melted	LL7
	Carbonaceous Chondrites 3.6% of falls Designations: "C" (for Carbonaceous Chondrite) followed by a letter to describe the type localities (except the H designation). Thenumber refers to level of alteration.	Ivuna		CI
		Mighei		CM1-CM2
		Vigarano.		CV2-CV3.3
		Renazzo		CR
		Ornans		CO3-CO3.7
		Karoonda		CK
		Bencubbin		CB
		High Iron		CH
	Enstatite Chondrites 1.5% of falls Designations: E stands for Enstatite H indicates high metallic iron L indicates low metallic iron		Abundant	E3, EH3, EL3
			Distinct	E4, EH4. EL4
			Less Distinct	E5, EH5, EL5
			Indistinct	E6, EH6, EL6
			Melted	E7
	Kakangari Chondrites			K
	Rumurutiite Chondrites			R
	Foresterite Chondrites			F
	Origin or Larger Grouping	Group	Minerals
Achondrites 7.8% of meteorite falls Achondrites are stony meteorites that lack chondrules. Some of these meteorites originated on the surface of the Moon and Mars.	Asteroidal Achondrites	Eucrites	basalts	EUC
		Diogenites	orthopyroxenites	DIO
		Howardites	brecciated basalts, orthopyroxenites	HOW
		Angrites	fassaitic-pyroxene basalts	ANGR
		Aubrites	Enstatite	AUB
		Ureilites	Olivine, pyroxene, carbonaceous	URE
		Brachinite	Olivine, clinopyroxene, orthopyroxene	BRACH
	Mars	Shergottites	Basalts and lherzolites	SHE
		Nakhlites	cumulus-augite-bearing pyroxenites	NAK
		Chassignite	dunite	CHA
	Lunar	Lunar - A (anorthositic), G (gabbros) , B (basalts), N(norites)	Basalt and Regolith	LUN
	Primitive Achondrites	Acapulcoite	plagoclase, troilite	ACAP
		Lodranites	plagioclase, troilite	LOD
		Winonaite	IAB-silicate related	WIN
			Widmanstatten Bandwidth
Irons (Structural classification) 4.8% of meteorite falls These meteorites are made of an iron-nickel alloy and are thought to originate from the cores of broken up differentiated parent bodies.	Hexahedrites <6% Ni. Contains kamacite, but not taenite		>50mm	H
	Octahedrites 6%-17% Ni. Contains both kamacite and taenite and exhibits Widmanstatten structure.	Coarsest	3.3-50mm	Ogg
		Coarse	1.3-3.3mm	Og
		Medium	0.5-1.3mm	Om
		Fine	0.2-0.5mm	Of
		Finest	0.2mm	Off
		Plessitic	0.2mm Kamacite spindles	Opl
	Ataxites High Ni content		Structureless	D
		Minerals	Structural Classes
Irons (Chemical Classification) A second scheme for classifying iron meteorites is based on their chemistry. Irons are classified into groups with similar ratios of trace elements to nickel. Generally, the higher the Roman numeral of the classification, the lower the concentration of trace elements. Iron meteorites that share a common origin or were formed under similar conditions should have a similar chemical classification.		kamacite, taenite, silicates, carbides	Om-Og	IAB
		kamacite, taenite, silicates, carbides	Om-Og	IC
		kamacite, taenite, (daubreelite)	Ogg, H	IIAB
		kamacite, aenite	Ogg	IIC
		kamacite, taenite	Of-Om	IID
		kamacite, taenite, silicates	Off-Og	IIE
		kamacite, taenite	Plessitic Oct., Atax.	IIF
		kamacite, taenite, troilite, phosphides	Om-Og	IIIAB
		kamacite, taenite, carbides	Off-D	IIICD
		kamacite, taenite, carbides, graphite	Og	IIIE
		kamacite, taenite	Om-Og	IIIF
		kamacite, taenite	Of	IVA
		kamacite, taenite	D	IVB
		kamacite, taenite, silicates, graphite	All	Anom
			Primary Minerals
Stony Irons 1.2% of meteorite falls These meteorites are mixtures of an iron-nickel alloy and non-metallic minerals and are thought to originate from the core-mantle boundary of a broken up differentiated parent body.	Pallasites	Main-group Pallasites	iron, olivine	PAL
		Eagle Station grouplet	iron, olivine, pyroxene	PAL
		Pyroxene Pallasite grouplet	iron, pyroxene	PAL
	Mesosiderites (MES) There are three broad petrologic groups designated A, B, and C. Within these groups there is a numeric classification of metamorphic grade. Grade 1 is fine grained and fragmental, 2 and 3 show progressive recrystallization, and 4 is a melt breccia.	Class A (Basaltic)	iron, Ca pyroxene, plagioclase	1A
				2A
				3A
				4A
		Class B (Ultramafic)	iron, Ca pyroxene, plagioclase, Orthopyroxene	1B
				2B
				3B
		Class C (Orthopyroxene)	orthopyroxene	2C