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Carbonaceous chondrites CV
Synonyms: Vigarano-like carbonaceous chondrites
General: The chondrites of the CV group are named for their type specimen, Vigarano a meteorite that fell in Emilia-Romagna, Italy, in 1910. However, the most famous CV member is without a doubt Allende, a meteorite that fell in a large shower in Mexico in 1969.
Description: CV chondrites are dark-grey rocks with black fusion crusts, and they are more dense, and less porous than the CI or CM chondrites. In fact, the structure and composition of these carbonaceous chondrites is more close to that of ordinary chondrites, and most of them belong to petrologic type 3. CV chondrites usually exhibit a 60:40 proportion of chondrules to matrix, and the chondrules are mostly large, and well defined. Typically, CV condrites also exhibit large CAIs (calcium-aluminium-inclusions) that will be discussed below.
Mineralogy: The matrix of CV chondrites mainly consists of iron-rich olivine, while the chondrules are made of magnesium-rich olivine, often surrounded by iron sulfide. The CAIs - white, irregular inclusions of different size that often make up more than 5% of the meteorite - are high-temperature minerals, and they are composed of silicates and oxides of calcium, aluminium, and titanium.
The chondrites of the CV group are further divided into three subgroups. The type specimen Vigarano and some other members belong to the reduced subgroup designated as CV3R. These CVs show a higher chondrule abundance as well as more reduced metal and less magnetite than the other two oxidized subgroups. One of these oxidized subgroups is named for Allende and has been designated as CV3OxA. The meteorites of this subgroup contain rare minerals like andradite, grossular, kirschsteinite, nepheline and others that aren't found in any other CV subgroup. The other oxidized subgroup is named for Bali and is designated as CV3OxB. The members of this subgroup represent the most oxidized CVs and show traces of aqueous alteration as well as phyllosilicates that aren't found in the other subgroups.
Origin and Formation: The large CAIs, characteristic of CV chondrites, have been intensely studied in the famous meteorite of Allende. Allende fell in Mexico in 1969, shortly before Neil Armstrong took his first step on the Moon. The CAIs of Allende contain fine-grained, microscopic diamonds - and those diamonds exhibit strange isotopic signatures that point to an origin outside of our solar system. They are interstellar grains that have proven to be older than the Earth and the Sun, and they are probably the product of a nearby supernova, of a dying star that made his last breath when our own system formed. Traces of this supernova have been trapped within the CAIs and preserved in the CV group and other carbonaceous chondrites up to this day.
Members: The CV group has about 65 members, but the number of actual CV falls has to be estimated to be somewhat lower since many of them are paired finds from the hot deserts of Africa, and the blue-ice fields of Antarctica. Famous historic and witnessed CV falls include Allende, Bali, Grosnaja, and the type specimen, Vigarano.