Allendeite, Sc₄Zr₃O₁₂, is an

oxide mineral The oxide mineral class includes those minerals in which the oxide anion (O2−) is bonded to one or more metal alloys. The hydroxide-bearing minerals are typically included in the oxide class. The minerals with complex anion groups such as the ...

. Allendeite was discovered in a small ultra

refractory In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase ...

inclusion within the

Allende meteorite The Allende meteorite is the largest carbonaceous chondrite ever found on Earth. The fireball was witnessed at 01:05 on February 8, 1969, falling over the Mexican state of Chihuahua. After it broke up in the atmosphere, an extensive search for p ...

. This inclusion has been named ACM-1. It is one of several

scandium Scandium is a chemical element with the symbol Sc and atomic number 21. It is a silvery-white metallic d-block element. Historically, it has been classified as a rare-earth element, together with yttrium and the Lanthanides. It was discovere ...

rich

minerals In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...

that have been found in

meteorites A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object e ...

. Allendeite is

trigonal In crystallography, the hexagonal crystal family is one of the six crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the trigonal crystal ...

, with a calculated

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematicall ...

of 4.84 g/cm³. The new mineral was found along with

hexamolybdenum Hexamolybdenum is a molybdenum dominant alloy discovered during a nanomineralogy investigation of the Allende meteorite. Hexamolybdenum was discovered in a small ultrarefractory inclusion within the Allende meteorite. This inclusion has been nam ...

. These minerals, are believed to demonstrate conditions during the early stages of the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

, as is the case with many CV3

carbonaceous chondrites 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 prop ...

such as the Allende meteorite. It is named after the Allende meteorite that fell in 1969 near

Pueblito de Allende The term Navajo Pueblitos, also known as Dinétah Pueblitos, refers to a class of archaeological sites that are found in the northwestern corner of the American state of New Mexico. The sites generally consist of relatively small stone and tim ...

Chihuahua Chihuahua may refer to: Places *Chihuahua (state), a Mexican state **Chihuahua (dog), a breed of dog named after the state **Chihuahua cheese, a type of cheese originating in the state **Chihuahua City, the capital city of the state **Chihuahua Mun ...

Mexico Mexico ( Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guate ...

Occurrence

Allendeite was found as nano-crystals in an ultra

inclusion in the

. The Allende meteorite has shown to be full of new minerals, after nearly forty years it has produced one in ten of the now known minerals in meteorites. This CV3

carbonaceous chondrite 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 prop ...

was the largest ever recovered on earth and is referred to as the best-studied meteorite in history. The inclusion has only been viewed via

electron microscopy An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a ...

. The sample is one centimeter in diameter and has been entrusted to the

Smithsonian Institution The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums and education and research centers, the largest such complex in the world, created by the U.S. government "for the increase and diffusion of knowledge". Founded ...

National Museum of Natural History The National Museum of Natural History is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States. It has free admission and is open 364 days a year. In 2021, with ...

with the catalog number USNM7554. One crystal studied is a single 15 x 25

micron The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer ( American spelling), also commonly known as a micron, is a unit of length in the International System of Un ...

size with included

perovskite Perovskite (pronunciation: ) is a calcium titanium oxide mineral composed of calcium titanate (chemical formula ). Its name is also applied to the class of compounds which have the same type of crystal structure In crystallography, crystal ...

, various

osmium Osmium (from Greek grc, ὀσμή, osme, smell, label=none) is a chemical element with the symbol Os and atomic number 76. It is a hard, brittle, bluish-white transition metal in the platinum group that is found as a trace element in alloys, mos ...

iridium Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal (after osmium) with a density of ...

molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with le ...

tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...

alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductilit ...

s, and scandium-stabilized tazheranite. In fact, all allendeite was in contact with perovskite. The grains are anhedral, with no observable crystal forms or twinning.

Significance

Various

rich minerals have been found in meteorites, including;

davisite Davisite is an exceedingly rare mineral of the pyroxene group, with formula CaScAlSiO6. It is the scandium-dominant member.Mindat, http://www.mindat.org/min-38829.html It stands for scandium-analogue of other pyroxene-group members, esseneite, gros ...

panguite Panguite is a type of titanium oxide mineral first discovered as an inclusion within the Allende meteorite, and first described in 2012. The hitherto unknown meteorite mineral was named for the ancient Chinese god Pan Gu, the creator of the wo ...

kangite Kangite is an exceedingly rare scandium mineral, a natural form of impure scandium oxide ), with the formula . It crystallizes in the cubic crystal system diploidal class. In terms of chemistry it scandium-analogue of tistarite. Both kangite and tis ...

, tazheranite,

thortveitite Thortveitite is a rare mineral consisting of scandium yttrium silicate (Sc,Y)2Si2O7. It is the primary source of scandium. Occurrence is in granitic pegmatites. It was named after Olaus Thortveit, a Norwegian engineer. It is grayish-green, black ...

, and eringaite. Of these, allendeite is the most Sc rich, with only pretulite containing substantially more scandium.

Appearance

Color Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are assoc ...

, streak, luster,

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion (mechanical), abrasion. In general, different materials differ in their hardn ...

tenacity Tenacity may refer to: * Tenacity (psychology), having persistence in purpose * Tenacity (mineralogy) a mineral's resistance to breaking or deformation * Tenacity (herbicide), a brand name for a selective herbicide * Tenacity (textile strength) * ...

cleavage Cleavage may refer to: Science * Cleavage (crystal), in mineralogy and materials science, a process of splitting a crystal * Cleavage (geology), the foliation perpendicular to stress as a result of ductile deformation * Cleavage (embryo), in emb ...

, fracture,

, and

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, o ...

could not be observed because the grain size was too small and the section bearing the mineral was optically thick.

References

{{Reflist, 30em Natural materials Trigonal minerals Minerals in space group 148 Oxide minerals

Occurrence

Significance

Appearance

See also

References