Earth Sciences 1086F/G Lecture Notes - Lecture 13: Achondrite, Basalt, Magnetite
13 Jan 2020
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1. Chapter 13: Meteorites
o - there are two categories that all meteorites appear under: - finds
- falls
o - Find: more or less stumble upon the meteorite and you have no idea when it
got there
o - Fall: a meteorite whose entry through the atmosphere has been
witnessed, and someone has recovered a piece of the object
Classification:
o - least sophisticated classification is irons, stony-irons, and stones
o - irons — consist almost entirely of iron and nickel metal alloys
o - stony-irons — a nearly 50-50 mix of the same metal alloys and a
non-metallic silicate/oxide material that looks like ordinary ‘stone’
o - stones — almost entirely the latter material
o - stones make up 93% of all known meteorites
▪ - they are subdivided into chondrites and achondrites
▪ - chondrites — considered aggregates of ‘cosmic sediment’ that
have never been altered nor melted greatly since first
compressed together
▪ - achondrites — igneous rocks that have been at least partially
melted and recrystallized
Chondrites:
o - the word chondrite derives from the ancient Greek word — chondros which
means grain or seed
o - specifically refers to the small inclusions in chondrites called chondrules
o - many ideas on how they formed
- popular idea: they condensed form a hot cloud of gas and dust, very early in
the solar system history, by a ‘flash-melting’ of dust aggregates in the solar
nebula
o - they are poorly blended aggregates of different materials: - nicely rounded
chondrules
- irregular shaped inclusions of various compounds
- shiny grains of metal alloys and metal sulfides
- dark fine grained matrix
o - process of clumping together the various products appearing in chondrites is
called accretion
o - the carbonaceous chondrites are of great importance
- they contain carbon which may be tiny diamonds, graphite, or even
hydrocarbon organic molecules
- contain many hydrous clay silicates as well as salts
Achondrites:
Document Summary
There are two categories that all meteorites appear under: - finds. Find: more or less stumble upon the meteorite and you have no idea when it got there. Fall: a meteorite whose entry through the atmosphere has been witnessed, and someone has recovered a piece of the object. Least sophisticated classification is irons, stony-irons, and stones. Irons consist almost entirely of iron and nickel metal alloys. Stony-irons a nearly 50-50 mix of the same metal alloys and a non-metallic silicate/oxide material that looks like ordinary stone". Stones almost entirely the latter material. Stones make up 93% of all known meteorites. They are subdivided into chondrites and achondrites. Chondrites considered aggregates of cosmic sediment" that have never been altered nor melted greatly since first compressed together. Achondrites igneous rocks that have been at least partially melted and recrystallized. The word chondrite derives from the ancient greek word chondros which means grain or seed.
