Machiite

Chemical formula: Al₂Ti₄+₃O₉

An extremely rare aluminum and titanium oxide, known exclusively from the Allende meteorite, named after a Japanese mineralogist.

## Characteristics Machiiite is a mineral known only from microscopic inclusions in the Allende meteorite, which fell in Mexico in 1969. It occurs as extremely small, subhedral (partially formed) grains, typically ranging from 1 to 10 micrometers in size. Due to its size, its visual characteristics cannot be assessed with the naked eye and require advanced analytical techniques, such as scanning electron microscopy. ## Physical Properties Due to the microscopic size of the grains, most of machiiite's physical properties, such as hardness, density, luster, or transparency, have not been directly measured, but only estimated based on its chemical composition and crystal structure. The density calculated from the formula and unit cell parameters is 4.61 g/cm³. ## Colors and Varieties In backscattered electron (BSE) images, where color depends on the average atomic number, machiiite appears dark gray. Its true color is unknown. No varieties of this mineral have been distinguished. ## History and Name The mineral was officially recognized by the International Mineralogical Association (IMA) in 2016 (IMA2016-029). The name honors Dr. Yasunori Miura (b. 1949), a retired professor from Yamaguchi University in Japan, for his contributions to extraterrestrial material research, including the analysis of impact craters. The discovery was made during the study of calcium-aluminum-rich inclusions (CAIs) in the famous Allende meteorite.

Properties

Density: 4.61
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of machiiite is possible only through advanced laboratory techniques. This requires chemical analysis using an electron microprobe (EDS/WDS) and structural studies by electron backscatter diffraction (EBSD) on polished meteorite samples. Its characteristic chemical composition (high titanium and aluminum content) and unique crystallographic structure are crucial for identification. ## Distinguishing from Similar Minerals Within CAI inclusions in the Allende meteorite, machiiite can be confused with other titanium and aluminum oxides, such as hibonite (CaAl₁₂O₁₉) or anosovite ((Ti³⁺,Ti⁴⁺)₂Ti⁴⁺O₅). Differentiation requires precise chemical analysis, as machiiite is characterized by a specific Al to Ti ratio and the absence of calcium, unlike hibonite. ## Crystal Forms Machiiite forms very small, subhedral grains, meaning its crystals are only partially developed and do not have fully formed, flat faces. It occurs as single, isolated grains within other minerals.

Geological environment

## Genesis Machiiite is a mineral of extraterrestrial origin. It formed at a very early stage of the Solar System's formation, under conditions of high temperature and low pressure, in a gas-rich protoplanetary cloud. It is believed to have condensed directly from gas or crystallized from a primordial melt within calcium-aluminum-rich inclusions (CAIs), which are among the oldest solids in our system. ## Mineral Associations Machiiite occurs in the Allende meteorite in close association with other minerals typical of CAIs, such as perovskite (CaTiO₃), spinel (MgAl₂O₄), and melilite (a group of minerals, mainly åkermanite and gehlenite). ## Localities The only confirmed locality for machiiite in the world is the Allende carbonaceous chondrite, which fell in Chihuahua, Mexico, on February 8, 1969. This is the type locality for this mineral.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, machiiite is not traded as a separate specimen. Its collector value is associated with the entire fragment of the Allende meteorite in which it was identified. For collectors and scientific institutions, specimens that have been studied and have documented presence of rare mineral phases, such as machiiite, are of greatest importance. The value of such a specimen depends on its size, provenance, and the quality of scientific documentation. ## Popular Localities The only source of machiiite is the Allende meteorite. Fragments of this meteorite are available on the collector's market, but those containing confirmed machiiite are mainly found in the collections of research institutions and universities.

Care and storage

## Cleaning Due to its microscopic size and occurrence exclusively as inclusions within other material, cleaning individual machiiite specimens is neither possible nor practiced. ## What to Avoid Specimens of the Allende meteorite containing machiiite should be protected from moisture, chemical contaminants, and extreme temperatures to preserve the integrity of the entire specimen. ## Storage The Allende meteorite, as the parent material for machiiite, should be stored under stable conditions, preferably in a dry environment (e.g., in a container with a desiccant), away from direct sunlight and contaminants, to prevent the degradation of associated minerals.

Sources

IMA Mineral List (CNMNC)