Howardites
Group · Stony meteorites › Chondrites › Carbonaceous chondrites

CV chondrites

Large chondrules and big white inclusions, the oldest solids in the Solar System. Allende is the classic.

CV chondrite
Allende, CV3, Mexico
Classification
Stony meteorites › Chondrites › Carbonaceous chondrites › CV chondrites
Share of witnessed falls
about 0.7%
In our catalogue
263 meteorites, 7 seen to fall
Heaviest
Allende, 2 t
Earliest recorded fall
Kaba, 1857
Most recent fall
Bukhara, 2001
Type specimen
Vigarano, fell in Italy in 1910

CV chondrites, named after Vigarano in Italy, have large chondrules and abundant white calcium-aluminium-rich inclusions (CAIs), often a centimetre or more across. These CAIs are dated to about 4,567 million years and mark time zero for the Solar System.

Almost all are petrologic type 3. They are divided into a reduced subgroup and two oxidised subgroups named after Allende and Bali. Allende, which fell in Mexico in 1969, is probably the most studied meteorite in the world.

Mineralogy and chemistry

CVs have large chondrules, often around 1 mm across, making up about 45% of the rock, and the highest proportion of CAIs of any group, up to about 10% by volume. Some CAIs are more than 2 cm across. The matrix, about 40% of the rock, is rich in iron-bearing olivine. Oxygen isotopes in CVs, and especially in their CAIs, plot far below Earth's line: CAIs are rich in oxygen-16, recording the isotopic make-up of the earliest solar gas.

Three subgroups are recognised. Reduced CVs, such as Vigarano, Efremovka and Leoville, still contain metal and sulphide. The oxidised Allende-like subgroup has magnetite and nickel-rich sulphides in place of metal, and the oxidised Bali-like subgroup also contains clays and other minerals formed by water. These differences reflect alteration by fluids on the parent body.

Parent body and formation

Some CVs carry a weak magnetisation thought to have been imprinted by a magnetic field lasting millions of years. That has led to the idea that their parent body had a molten metal core under an unmelted chondritic crust: a partly differentiated asteroid. CK chondrites share their oxygen isotopes and may be more heated material from the same body.

Studies of aluminium-26 in CV CAIs, first made on Allende in the 1970s, showed that this short-lived isotope was present in the early Solar System, providing the main heat source that melted the first planetesimals.

Abundance and famous examples

CVs are about 0.7% of falls. Allende fell over Chihuahua, Mexico, before dawn on 8 February 1969, scattering more than two tonnes of stones over a field about 50 km long. It became the standard sample for CAIs and early Solar System dating. Vigarano fell near Ferrara, Italy, in 1910. Kaba, which fell in Hungary in 1857, was one of the first meteorites in which organic matter was studied. Mokoia (New Zealand, 1908) and Bali (Central African Republic, 1907) are other notable falls.

Research highlights

CV inclusions have yielded a long list of new minerals: dozens have been described from Allende alone, many of them known only from meteorites. Allende is also used as a reference rock: a powdered sample was distributed to laboratories as a standard for chemical analysis. Because its stones were so plentiful, generous amounts went to museums and schools, and Allende pieces are still among the easiest carbonaceous chondrites for collectors to own.

How to recognise one

A CV is unmistakable on a cut face: grey rock speckled with large dark chondrules and irregular white or pinkish CAIs, often several millimetres to centimetres across. The fusion crust is black and the stone weakly magnetic. Desert finds of CVs are often brown and may be mistaken for ordinary chondrites until cut.

Famous examples

Related groups

See all 263 CV chondrites

Photos shared under Creative Commons licences (Wikimedia Commons).