Meteorite composition
• Major groupings:
– Stony meteorites
• Chondrites
• Achondrites
– Iron meteorites
• Octahedrites, hexahedrites, ataxites
– Stony-iron meteorites
• Pallasites
• Mesosiderites
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Chondrites
Carbonaceous chondrite class
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CI chondrite (Ivuna-like) group
CM-CO chondrite (mini-chondrule) clan
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CM chondrite (Mighei-like) group
CO chondrite (Ornans-like) group
CV-CK chondrite clan
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CV chondrite (Vigarano-like) group
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–
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CK chondrite (Karoonda-like) group
CR chondrite clan
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CR chondrite (Renazzo-like) group
CH chondrite (Allan Hills 85085-like) group
CB chondrite (Bencubbin-like) group
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–
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H chondrite group
L chondrite group
LL chondrite group
Enstatite chondrite class
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CBa chondrite subgroup
CBb chondrite subgroup
Ordinary chondrite class
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CV-oxA chondrite (oxidized, Allende-like) subgroup
CV-oxB chondrite (oxidized, Bali-like) subgroup
CV-red chondrite (reduced) subgroup
EH chondrite group
EL chondrite group
Other chondrite groups, not in one of the major classes
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R chondrite (Rumuruti-like) group
K chondrite (Kakangari-like) grouplet (a grouplet is a provisional group with <5 members)
Chondrites
• Stony meteorites – most common meteorites and
represent the oldest solids that are the building
blocks of the solar system
• Parent bodies were small-medium asteroids, not
planetoids!
• Contain up to 80% chondrules, which were freely
floating molten drops in space
• Few mm to 1 cm spheres
• Mostly olivine and
pyroxene, also feldspathic
glass or crystals with minor
troilite (FeS), chromite,
phosphates
• 15 groups of chondrites
Chondrite groups
• Ordinary – make up 80% of the meteorites and
90% of chondritic meteorites, abundant chondrules,
variable Fe-Ni lead to H, L, and LL chondrites
• Carbonaceous chondrites –less the 5% of
chondritic meteorites, few chondrules, more
lithophile elements (Ca, Mg, K, Cr, Al, Cl,…), high
levels of water and organic compounds - many
types based on characteristic specimen
• Enstatite Chondrites – 2% of chondritic meteorites,
very chemically reduced – enstatite-rich chondrules
and abundant metal and sulfide minerals
Peekskill Meteorite
Peekskill Meteor: October 9, 1992. This famous fireball was seen and
filmed across several eastern states. It broke up into many
fragments, one of which hit the trunk of Michelle Knapp's 1980
Chevy Malibu. When Ms. Knapp investigated a crash sound outside
her Peekskill, NY home, she discovered the damaged trunk and
found a warm 12-kg meteorite lying beside the car.
12-kg Ordinary
Chondritic
meteorite
Car – $10K
Meteorite – $75K
Achondrites
• Stony meteorite similar to terrestrial basalts or
plutonic rocks, represent 8% of meteorites grouped
on the basis of Fe/Mn and 17O/18O ratios
characteristic of the parent body
• 2/3 of these meteorites are HED type, originating
from one asteroid, Vesta 4 - there is a large impact
crater observed on this asteroid
• Also includes Martian and lunar meteorites
The Johnstown Diogenite.
Lunar Meteorite Allan Hills 81005
Martian Meteorites
• All are igneous, lherzolitic to basaltic composition, and
some contain hydrated carbonates and sulfates,
evidence of liquid water
• ALH84001 is 4.5 ga, contains carbonate veins 3.6 – 4
ga, Organic matter (PAH), aligned magnetite crystals,
proposed nanofossils (careful!!) – very controversial…
ALH84001
ALH84001 – round
carbonate grains
Nahkla Meteorite
Iron Meteorites
• 5% of meteorites, but 90% of the mass of recovered
meteorites and all of the largest meteorites (66 tons is the
record) - primarily composed of iron-nickel alloy
intergrowths:
– Kamacite – Fe-Ni alloy at 90:10 to 95:5 Fe:Ni
– Taenite – Fe-Ni alloy at 80:20 to 45:65 Fe:Ni
– Widmanstätten pattern – finely interweaved Kamacite and Taenite
(Octahedrites)
• Classified on Ni content:
Ataxites>Octahedrites>Hexahedrites
Stony-iron Meteorites
• Mix of iron-nickel alloy and silicate
minerals (mostly olivine), 1% of meteorites
– Pallasites are thought to form a the coremantle boundary of differentiated asteroids
– Mesosiderite – equal parts metal alloy and
silicate with a breccia texture
Identifying a meteorite
• Fusion crust – dull black to dark brown,
often soft, can be weathered to red (but
can flake off)
• Density – generally dense
• Chondrules are specifically meteoritic
• Never porous, but can be ‘dimpled’ with
surface depressions
• 99% of meteorites are magnetic
• Unusually high Ni content
• Fusion crust forms on entry through the
atmosphere
Meteorite/ Comet Impacts
• P/T space??
Discovering the K/T impact
• Iridium elevated
in very thin layer
worldwide
• Alvarez and his
students/
postdocs
postulated this in
late 1979…
Chicxulub, Yucatan Peninsula,
Mexico
• K/T event at 64.98 ma, formed from a 6-12 mile
diameter asteroid impact (50 megaton blast)
Barringer Meteor Crater, Arizona, formed from Can
Impact Craters
• Many famous impact craters,
hundreds known on earth
(why might there have been
plenty more??)
– Sudbury, Ontario (250km
diameter, 1.85 ga)
– Chesapeake Bay (90km
diameter, 35 ma)
– Manson, Iowa (35km, 74ma)
– Barringer, Arizona (1.2km, 49
ka)
– Serpent Mound, Ohio (8km,
320 ma)
Clearwater lakes, Quebec –
36+26km diameter, 290
ma
Megatsunamis
• Meteorite impact in the ocean displaces
huge quantities of water instantly
• The Chixculub crater impact generated a
megatsunami 150-300 feet high
Energy of an impact
• Kinetic energy – going from
very fast to stopping is a BIG
change in energy
• What happens to that
energy??
• Impactite – any mineral formed
as a result of this impact
Shatter cone
Materials indicating Meteorite
Impacts
• Tektites
• Glass formed from impact
Diaplectic Glass
• Glass formed through fusion of different
minerals – not melted, but fused…
What Happens to minerals that
are there but not melted?
• Shock Quartz
• Lamellae retaining evidence of impact
Diamonds
• Very small diamonds can form from
impacts and are found in meteorite impact
craters around the world
• Diamonds can also form in meteoritesthese can be gray to black
• Lonsdalite - Hexagonal
allotrope of diamond,
specific to meteorite
impacts, thought to
form from graphite in
meteorites
Quartz Polymorphs
• Coesite and Stishovite found associated with
impact craters