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However, there are significant differences between R chondrites and ordinary chondrites: R chondrites have much more dusty matrix material (about 50% of the rock); they are much more oxidized, containing little metallic Fe–Ni; and their enrichments in 17 O are higher than those of ordinary chondrites. Nearly all the metal they contain is ...
Primitive achondrites are a subdivision of meteorites. They are classified on the same rank (historically called "Class") and lying between chondrites and achondrites . They are called primitive because they are achondrites that have retained much of their original chondritic properties.
An achondrite [1] is a stony meteorite that does not contain chondrules. [ 2 ] [ 3 ] It consists of material similar to terrestrial basalts or plutonic rocks and has been differentiated and reprocessed to a lesser or greater degree due to melting and recrystallization on or within meteorite parent bodies.
Because ordinary chondrites represent 80% of the meteorites that fall to earth, and because ordinary chondrites contain 60–80% chondrules, it follows that (excluding dust) most of the meteoritic material that falls on earth is made up of chondrules. Chondrules can range in diameter from just a few micrometers to over 1 centimetre (0.39 in).
Carbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 8 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites. The C chondrites represent only a small proportion (4.6%) [1] of meteorite falls.
Ordinary chondrite NWA 3189 sliced. Field of view c. 2.2 cm across. NWA 3189 has been classified as an LL3.2–3.4 ordinary chondrite ("LL" means very low total iron content; "3" refers to well-preserved chondrules – the rock has not been subjected to metamorphism intense enough to disrupt the chondritic texture).
This, together with the low content of metal, led the 19th century mineralogist Tschermak to determine that they formed a transitional stage between chondrites and achondrites and to name them amphoterites. [2] We know now that LL chondrites and achondrites are quite different, so this name is no longer in use. Many of the LL chondrites are ...
Chondrites are often considered to be "the building blocks of the planets". About 8% of the meteorites are achondrites (meaning they do not contain chondrules), some of which are similar to terrestrial igneous rocks. Most achondrites are also ancient rocks, and are thought to represent crustal material of differentiated planetesimals.