Carbonaceous chondritesChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such represent the most primitive rock samples of our solar systemThe Sun and set of objects orbiting around it including planets and their moons and rings, asteroids, comets, and meteoroids.. This rare (less than 5% of all meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and falls) class of meteorites are a time capsule from the earliest days in the formation of our solar systemDefinable part of the universe that can be open, closed, or isolated. An open system exchanges both matter and energy with its surroundings. A closed system can only exchange energy with its surroundings; it has walls through which heat can pass. An isolated system cannot exchange energy or matter with. They are divided into the following compositional groups that, other than CH (High MetalElement that readily forms cations and has metallic bonds; sometimes said to be similar to a cation in a cloud of electrons. The metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. A diagonal line drawn) and C-UNG (UngroupedModifying term used to describe meteorites that are mineralogically and/or chemically unique and defy classification into the group or sub-group they most closely resemble. Some examples include Ungrouped Achondrite (achondrite-ung), Ungrouped Chondrite (chondrite-ung), Ungrouped Iron (iron-ung), and Ungrouped Carbonaceous (C-ung).), are named after the first or most prominent meteorite of that type: CB (Bencubbin), CI (Ivuna), CK (Karoonda),CM (Mighei), CO (Ornans), CR (Renazzo) and CV (Vigarano). CI and CM meteorites (and comets) are rich in organicPertaining to C-containing compounds. Organic compounds can be formed by both biological and non-biological (abiotic) processes. compounds and water that, as precursors to life, played a critical role in the development of life on Earth. The term “carbonaceous” is a misnomer in that they contain relatively little carbonElement commonly found in meteorites, it occurs in several structural forms (polymorphs). All polymorphs are shown to the left with * indicating that it been found in meteorites and impact structures: a. diamond*; b. graphite*; c. lonsdalite*; d. buckminsterfullerene* (C60); e. C540; f. C70; g. amorphous carbon; h. carbon nanotube*..... Expand
Further discriminating characteristics are distinct abundances of high-temperature components such as chondrulesRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine and Calcium Aluminum Inclusions (CAIsSub-millimeter to centimeter-sized amorphous objects found typically in carbonaceous chondrites and ranging in color from white to greyish white and even light pink. CAIs have occasionally been found in ordinary chondrites, such as the L3.00 chondrite, NWA 8276 (Sara Russell, 2016). CAIs are also known as refractory inclusions since they), opaque phases and the fine-grained matrixFine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents., as well as the degree of bulk chondriteChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such alteration. Chondrules are products of transient heating events of unknown origin and depleted in volatile elementsChemical elements that condense (or volatilize) at relatively low temperatures. The opposite of volatile is refractory. Volatile elements can be divided into moderately volatile (Tc = 1230–640 K) and highly volatile (Tc < 640 K). The moderately volatile lithophile elements are: Mn, P, Na, B ,Rb, K, F, Zn. The moderately relative to their host bulk chondrite. In contrast, the matrix is enriched in volatileSubstances which have a tendency to enter the gas phase relatively easily (by evaporation, addition of heat, etc.). elements relative to the bulk chondrite. CI chondrites almost entirely consist of matrix and no chondrules. Their relative volatile elemental abundances, compared to all other meteorite classes, most closely matches those of the solar photospherePoint where a star's atmosphere appears to become completely opaque. Thus, the photosphere may be thought of as the imaginary surface from which the starlight that we see appears to be emitted. The photosphere is not a thin surface; the Sun's photosphere has a thickness of ~100 km. (Within that, attesting to their primitive chemical composition. Virtually all other known planetary materials, i.e., other groups of meteorites, the terrestrial planetsRocky planets: Mercury, Venus, Earth, and Mars. These planets have physical characteristics, chemical composition and internal structure similar to the Earth. The terrestrial planets have 0.4% of the total mass of all the planets in the Solar System. Some large satellites of planets are also similar to the characteristics of and the Moon are significantly depleted in volatile elements (e.g. Na, K, Zn, S, Cd) relative to CI.
The definition above is a highly modified version of the introductory paragraph from “The Chemical Composition of Carbonaceous Chondrites” by Braukmüller et al., 2018.
In addition to silicates, oxides, and sulfides, a subset of carbonaceous chondrites also contain water and/or aqueously altered minerals such as serpentineName used for a large group of phyllosilicate minerals with the generalized formula X2-3 Y2 O5 (OH)4. Due to their various structures (meteoritics focuses primarily on (Fe, Mg)3Si2O5(OH)4), serpentine can be used to understand the chemistry and progress of aqueous alteration (hydration) of olivine, amphibole, or pyroxene dating back to, together with broad range of organic compounds, such as amino acids, that are precursors and building blocks to life.
Petrologic typeMeasure of the degree of aqueous alteration (Types 1 and 2) and thermal metamorphism (Types 3-6) experienced by a chondritic meteorite. Type 3 chondrites are further subdivided into 3.0 through 3.9 subtypes. indicates the degree of either aqueous or thermal alteration experienced by chondritic meteorites. Aqueous alteration occurred in the parent bodyThe body from which a meteorite or meteoroid was derived prior to its ejection. Some parent bodies were destroyed early in the formation of our Solar System, while others like the asteroid 4-Vesta and Mars are still observable today. under temperatures probably in the range of 20 °C to 50 °C in a water-rich environment. This contrasts to the thermal metamorphism of ordinary chondrites that occurred in the range of 600 °C to 900 °C under very dry conditions. Carbonaceous chondrites may contain up to 20 weight % water. Different groups of carbonaceous chondrites have been identified that came from parent bodies in different parts of the solar nebulaThe primitive gas and dust cloud around the Sun from which planetary materials formed..
Some or all content above used with permission from J. H. Wittke.
