HowarditeOne type of meteorite in the HED (Howardite, Eucrite, Diogenite) achondrite group. Howardites are named after the English chemist Edward Howard (1774-1816), one of the pioneers of meteoritics. Consisting mostly of eucritic and diogenitic clasts and fragments, howardites are polymict breccias. However, they can also contain dark clasts of carbonaceous Click on Term to Read More
RegolithMixture of unconsolidated rocky fragments, soil, dust and other fine granular particles blanketing the surface of a body lacking an atmosphere. Regolith is the product of "gardening" by repeated meteorite impacts, and thermal processes (such as repeated heating and cooling cycles). Click on Term to Read More brecciaWork in Progress ... A rock that is a mechanical mixture of different minerals and/or rock fragments (clasts). A breccia may also be distinguished by the origin of its clasts: (monomict breccia: monogenetic or monolithologic, and polymict breccia: polygenetic or polylithologic). The proportions of these fragments within the unbrecciated material Click on Term to Read More
Fell April 22, 1942
31° 10′ S., 127° 45′ E.
An 11.355 kg stone ~18 cm in diameter fell in Equatoria, South Sudan, at 7:00 in the evening. The mass was recovered on the Kapoeta–Nathalani Road. The main massLargest fragment of a meteorite, typically at the time of recovery. Meteorites are commonly cut, sliced or sometimes broken thus reducing the size of the main mass and the resulting largest specimen is called the "largest known mass". Click on Term to Read More
currently resides with the Sudan Geological Survey in Khartoum.
Kapoeta has a composition of a microbreccia formed through impact gardening of the compacted regolith of its 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. Click on Term to Read More
, probably the asteroid/planetoid 4 VestaThird largest and fourth brightest asteroid; it was discovered in 1807 by Heinrich Olbers and named for the ancient Roman goddess of the hearth. 4 Vesta has a basaltic surface composition and an average density not much less than that of Mars. Evidently lava once flowed here indicating that the
. Kapoeta consists of mineralInorganic substance that is (1) naturally occurring (but does not have a biologic or man-made origin) and formed by physical (not biological) forces with a (2) defined chemical composition of limited variation, has a (3) distinctive set of of physical properties including being a solid, and has a (4) homogeneous Click on Term to Read More
and rock fragments, primarily eucriteMost common type of achondrite meteorite and a member of the HED group. Eucrites are basalts composed primarily of pigeonite and anorthite (An60-98). Eucrites have been placed into three subgroups based on mineralogical and chemical differences. • Non-cumulate eucrites represent the upper crust that solidified on a magma ocean after Click on Term to Read More
and diogeniteDiogenites belong to the evolved achondrite HED group that also includes howardites and eucrites. They are named after the Greek philosopher Diogenes of Apollonia, of the 5th century BCE, who was the first to suggest that meteorites come from outer space (a realization forgotten for over 2,000 years). They are Click on Term to Read More
sourced, having a mixing ratio of 2 parts eucritic to 1 part diogenitic material, and which spans the known range of Fe/(Fe+Mg) ratios of HED samples. This mixing ratio corresponds to an Al-oxide content near 8–9 wt%, which some have defined as a compositional cluster to which the regolithic howardites belong. Kapoeta has a cumulateIgneous rock composed of crystals that have grown and accumulated (often by gravitational settling) in a cooling magma chamber. Click on Term to Read More
/noncumulate eucriteMost common type of achondrite meteorite and a member of the HED group. Eucrites are basalts composed primarily of pigeonite and anorthite (An60-98). Eucrites have been placed into three subgroups based on mineralogical and chemical differences. • Non-cumulate eucrites represent the upper crust that solidified on a magma ocean after Click on Term to Read More
ratio commensurate with that of known eucritesMost common type of achondrite meteorite and a member of the HED group. Eucrites are basalts composed primarily of pigeonite and anorthite (An60-98). Eucrites have been placed into three subgroups based on mineralogical and chemical differences. • Non-cumulate eucrites represent the upper crust that solidified on a magma ocean after Click on Term to Read More
. Unlike most howardites which are fragmental breccias, Kapoeta is one of a small number of howardites that are distinguished as regolithic breccias (e.g.
, LEW 85313, MET 00423, PRA 04401, SCO 06040, and EET 87513) (Warren et al.
, 2009; Cartwright et al.
, 2012). Consistent with this category, Kapoeta is enriched in solar-wind noble gasesElement occurring in the right-most column of the periodic table; also called "inert" gases. In these gases, the outer electron shell is completely filled, making them very unreactive. Click on Term to Read More
, contains high siderophile abundances (e.g.
, >300 PPMParts per million (106).
Ni; high Ir), contains an abundance of glasses (mostly spheroidal or turbid-brown), and incorporates xenoliths of black, carbonaceous chondriteCarbonaceous chondrites represent the most primitive rock samples of our solar system. This rare (less than 5% of all meteorite falls) class of meteorites are a time capsule from the earliest days in the formation of our solar system. They are divided into the following compositional groups that, other than Click on Term to Read More
fragments and microclasts. The carbonaceous (CM) fragments are probably a late addition to the regolith breccia, and contain planetary gases in addition to solar-wind implanted gases (Cartwright et al.
In a study of regolithic howardites conducted by Cartwright et al.
(2013), it was concluded that noble gasElement occurring in the right-most column of the periodic table; also called "inert" gases. In these gases, the outer electron shell is completely filled, making them very unreactive. Click on Term to Read More
analysis is the most important indicator among those used for determining a regolithic origin. They resolved two trends that exist among regolithic howardites: 1) the presence of a trapped solar windSupersonic flow of high-speed charged particles continuously blowing off a star (mostly e- and p+). When originating from stars other than the Sun, it is sometimes called a "stellar" wind. The solar wind may be viewed as an extension of the corona into interplanetary space. The solar wind emanates radially
or fractionated solar wind noble gas component, and/or 2) the presence of a planetary noble gas component (such as the dominant Q-gases or the exotic HL-noble gases), known to be associated with xenolithic carbonaceous 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 Click on Term to Read More
clasts; the presence of only cosmogenic noble gases is not prognostic of a regolithic origin.
It is proposed by Warren et al.
(2009) that the regolithic howardites represent a rare ancient phase of regolith gardening that has since been destroyed within the last 1 b.y. in the large impact which produced the Vestoids. The tight clustering of the Al-oxide composition near 8–9 wt% and the consistency of the ~1:2 mixing ratio of eucrite to diogeniteDiogenites belong to the evolved achondrite HED group that also includes howardites and eucrites. They are named after the Greek philosopher Diogenes of Apollonia, of the 5th century BCE, who was the first to suggest that meteorites come from outer space (a realization forgotten for over 2,000 years). They are Click on Term to Read More
for the regolithic howardites infers a single large impact excavation into shallow eucrite and deeper diogenite layers; these layers were proportionately equal with respect to asteroid radius. This was followed by shallow lateral mixing and homogenization to produce a specific regolith grade/maturity consistent with a high diversity of components. The high siderophile content of the regolithic howardites compared to other HED breccia types is consistent with an extended period of impact gardening that homogenized impactor and regolith materials.
The larger carbonaceous impactor fragments are composed of fine-grained matrixFine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. Click on Term to Read More
material with embedded 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 Click on Term to Read More
resembling those of the CM2 type, while the carbonaceous chondrite microclasts (CCMs) are smaller than 1 mm and comprise three different types: 1) tochilinite-rich, consistent with CM2 chondrite material; 2) magnetite-rich, olivine-poor; and 3) magnetite-rich, olivine-rich, the latter two types having no representative meteorites in our collections (Gounelle et al.
, 2005). In common with Antarctic micrometeorites, these three CCM types have a combined D/H ratio nearly identical to that of the Earth, and it is argued that CCMs might represent the same material which delivered water to the accreting Earth, a theory consistent with research results obtained by the Carnegie Institution for Science and published in Science Express
, July 12, 2012. In their analysis of platinum group elementsElements with geochemical properties similar to Pt (platinum) including Ru, Rh, Pd, Os, Ir, and sometimes Au. These occur in nature in close association with one another and with Ni and Cu. They are among the least abundant of the Earth’s naturally occurring elements. Click on Term to Read More
to discern the impactor types present in howardites, Wee et al.
(2010) identified a wide variety of material including various subgroups of carbonaceous, ordinary, and enstatiteA mineral that is composed of Mg-rich pyroxene, MgSiO3. It is the magnesium endmember of the pyroxene silicate mineral series - enstatite (MgSiO3) to ferrosilite (FeSiO3). Click on Term to Read More 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 Click on Term to Read More
. Kapoeta exhibits high abundances of impactor material equivalent to ~10% chondritic debris, with 2–3% comprising CM chondriteClass of carbonaceous chondrites named after the Mighei meteorite that fell in Ukraine in 1889. They represent samples of incompletely serpentinized primitive asteroids and have experience extremely complex histories. CM meteorites are generally petrologic level type 2 though a few examples of CM1 and CM1/2 also exist. Compared to CI Click on Term to Read More
Also present in the Kapoeta regolith breccia are impact-melt clasts of howardite material, as well as glass spherules which have been shown to be a product of impact rather than fire-fountaining (Boesenberg and Mandeville, 2007). All of these disparate components were mixed together over eons of continuous bombardment to the surface of the HED-parent asteroid. Based on Hf–W systematics of a limited number of howardites, an isochron was gleaned which is consistent with ages previously determined for eucrites and diogenitesDiogenites belong to the evolved achondrite HED group that also includes howardites and eucrites. They are named after the Greek philosopher Diogenes of Apollonia, of the 5th century BCE, who was the first to suggest that meteorites come from outer space (a realization forgotten for over 2,000 years). They are Click on Term to Read More
(Lee and Fukuyama, 2009). A breccia compaction age of 2 b.y. has been calculated by investigators. As evidenced by the presence of solar-wind-implanted noble gases, Kapoeta was part of a regolith on its parent body for at least a time, and a high Ni content has been found to be diagnostic of such a regolithic origin. This regolith residence was followed by a period of burial lasting several millions of years which drove 26
Al to extinctionIn astronomy, the dimming of starlight as it passes through the interstellar medium. Dust scatters some of the light, causing the total intensity of the light to diminish. It is important to take this effect into account when measuring the apparent brightness of stars. The dark bands running across portions Click on Term to Read More
. Based on data from the cosmogenic radionuclideRadioactive isotope - Atomic nuclide that decays radioactively . Click on Term to Read More 36
Cl, a CRE age of ~3 m.y. was derived. These data also suggest that the meteoroidSmall rocky or metallic object in orbit around the Sun (or another star).
had a pre-atmospheric diameter of ~40 cm and that the Kapoeta 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 Click on Term to Read More
had been located several cm deep within this meteoroid.
Studies of orthopyroxeneOrthorhombic, low-Ca pyroxene common in chondrites. Its compositional range runs from all Mg-rich enstatite, MgSiO3 to Fe-rich ferrosilite, FeSiO3. These end-members form an almost complete solid solution where Mg2+ substitutes for Fe2+ up to about 90 mol. % and Ca substitutes no more than ~5 mol. % (higher Ca2+ contents occur Click on Term to Read More
crystals from selected howardites indicate a magnesium concentration in Kapoeta consistent with that of diogenites (Domeneghetti et al.
, 2000, 2004). The presence of exsolved augiteHigh-Ca clinopyroxene, (Ca,Mg,Fe)SiO3, that occurs in many igneous rocks, particularly those of basaltic composition. In order to be considered augite, the clinopyroxene must contain 20 to 45 mol % of calcium (Wo20 - 45). An important and unique Martian meteorite is NWA 8159, that has been classified as an augite Click on Term to Read More
, along with a slow cooling rate, suggests an origin of Kapoeta within a deep, plutonicGeology: Igneous intrusive body that forms when magma is injected into host rocks and solidifies. Plutons occur in the crust of asteroids undergoing differentiation or planets. Named after Pluto, the Roman god of the underworld. Plutonic rocks are the rocks found within a pluton. Astronomy: Category of planet including all Click on Term to Read More
, diogenitic source region, which experienced an ejection by impact. A more detailed scenario for the formation of the HED clan can be found on the Millbillillie
The basaltic achondriteAn achondrite is a type of stony meteorite whose precursor was of chondritic origin and experienced metamorphic and igneous processes. They have a planetary or differentiated asteroidal origin where the chondritic parent body reached a sufficient size that through heating due to radioactive decay of 26Al (aluminum isotope) and gravitational Click on Term to Read More
group is a complicated one to classify due to the diversity in the structural and mineralogical relationships among its members. This group is composed of brecciated and unbrecciated, monomict and polymict eucrites, diogenites, and howardites, and has recently undergone a redefinition. The monomict subgroup containing eucrites, cumulate eucrites, and diogenites is further subdivided into brecciated and unbrecciated members. The polymict subgroup samples a compositional and textural continuum of regolith and surface breccias consisting of eucrites, cumulate eucrites, diogenites, and howardites. Those meteorites containing more than 90% of a single component are given the prefix ‘polymict’ attached to their present description (e.g.
polymict eucrites contain less than 10% non-eucritic material; polymict diogenites contain more than 90% orthopyroxeniteA rock composed primarily of orthopyroxene. Non-terrestrial orthopyoxenites include diogenites and a single martian meteorite, ALH 84001, that was found in the Allan Hills region of Antarctica in 1984. ALH 84001 is a cumulate rock consisting of 97% coarse-grained, Mg-rich orthopyroxene, with small amounts of plagioclase, chromite, and carbonate. It Click on Term to Read More
). Those meteorites that contain less than 90% of any single component are defined as howardites. While this 10% level is still an arbitrary dividing line based simply on mineral mixing proportions, it represents an amount of orthopyroxene that can easily be detected by X-ray diffractionAnalytical technique used to determine the structures of crystalline solids. A monochromatic beam of X-rays (usually Cu-Kα) is diffracted off repeating planes of atoms in crystalline samples to produce a diffraction pattern. Through analysis of the diffraction pattern, atomic structures can often be determined.
techniques. An additional tool to distinguish polymict eucrites from howardites involves pyroxenes in the basaltic clasts—in howardites they are mostly unzoned, whereas in polymict eucrites they are usually zoned. The number of howardites in our collections is about one-third the number of eucrites and slightly less than the number of diogenites; however, the compositionally distinct subset of regolithic howardites is much more poorly sampled (Warren et al.
, 2009). A transmitted light view of a petrographic thin sectionThin slice or rock, usually 30 µm thick. Thin sections are used to study rocks with a petrographic microscope.
of Kapoeta can be seen on J. Kashuba’s page
. The Kapoeta specimen pictured above is a 2.4 g partial slice.