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. Minerals with complex anion groups such as the sil ...

. Allendeite was discovered in a small ultra

refractory In materials science, a refractory (or refractory material) is a material that is resistant to decomposition by heat or chemical attack and that retains its strength and rigidity at high temperatures. They are inorganic, non-metallic compound ...

inclusion Inclusion or Include may refer to: Sociology * Social inclusion, action taken to support people of different backgrounds sharing life together. ** Inclusion (disability rights), promotion of people with disabilities sharing various aspects of lif ...

within the Allende meteorite. This inclusion has been named ACM-1. It is one of several

scandium Scandium is a chemical element; it has Symbol (chemistry), symbol Sc and atomic number 21. It is a silvery-white metallic d-block, d-block element. Historically, it has been classified as a rare-earth element, together with yttrium and the lantha ...

rich

minerals In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): M ...

that have been found in

meteorites A meteorite is a rock that originated in outer space and has fallen to the surface of a planet or moon. When the original object enters the atmosphere, various factors such as friction, pressure, and chemical interactions with the atmospheri ...

. Allendeite is

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

, with a calculated

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

of 4.84 g/cm³. The new mineral was found along with hexamolybdenum. These minerals, are believed to demonstrate conditions during the early stages of the

Solar System The Solar SystemCapitalization 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 "Sola ...

, as is the case with many CV3 carbonaceous chondrites such as the Allende meteorite. It is named after the Allende meteorite that fell in 1969 near Pueblito de Allende, Chihuahua,

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

Occurrence

Allendeite was found as nano-crystals in an ultra

inclusion in the Allende meteorite. 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 propo ...

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 electrons as a source of illumination. It uses electron optics that are analogous to the glass lenses of an optical light microscope to control the electron beam, for instance focusing i ...

. 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, Education center, education and Research institute, research centers, created by the Federal government of the United States, U.S. government "for the increase a ...

National Museum of Natural History The National Museum of Natural History (NMNH) 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. With 4.4 ...

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

micron The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...

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 as , known as the perovskite (stru ...

, various

osmium Osmium () is a chemical element; it has Symbol (chemistry), symbol Os and atomic number 76. It is a hard, brittle, bluish-white transition metal in the platinum group that is found as a Abundance of elements in Earth's crust, trace element in a ...

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

molybdenum Molybdenum is a chemical element; it has Symbol (chemistry), symbol Mo (from Neo-Latin ''molybdaenum'') and atomic number 42. The name derived from Ancient Greek ', meaning lead, since its ores were confused with lead ores. Molybdenum minerals hav ...

tungsten Tungsten (also called wolfram) is a chemical element; it has symbol W and atomic number 74. It is a metal found naturally on Earth almost exclusively in compounds with other elements. It was identified as a distinct element in 1781 and first ...

alloy An alloy is a mixture of chemical elements of which in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...

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, gro ...

, panguite, kangite, tazheranite,

thortveitite Thortveitite is a rare mineral consisting of scandium yttrium silicate (Sc,Y)2Si2O7. It is the most widespread scandium mineral, but natural thortveitite is not widely exploited as a source of scandium metal. Most scandium is derived from mine ta ...

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

Appearance

Color Color (or colour in English in the Commonwealth of Nations, Commonwealth English; American and British English spelling differences#-our, -or, see spelling differences) is the visual perception based on the electromagnetic spectrum. Though co ...

, streak, luster,

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to plastic deformation, such as an indentation (over an area) or a scratch (linear), induced mechanically either by Pressing (metalworking), pressing or abrasion ...

, tenacity,

cleavage Cleavage may refer to: Science * Cleavage (crystal), the way in which a crystal or mineral tends to split * Cleavage (embryo), the division of cells in an early embryo * Cleavage (geology), foliation of rock perpendicular to stress, a result of ...

fracture Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress (mechanics), stress. The fracture of a solid usually occurs due to the development of certain displacemen ...

, and

refractive index In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...

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