Hiroseite
Chemical formula: Fe<sup>2+</sup>SiO<sub>3</sub>
Hiroseite is an extremely rare mineral from the pyroxene group, a high-pressure polymorph of ferrosilite, discovered in a meteorite.
Description
## Characteristics Hiroseite is a mineral from the orthopyroxene group, representing a high-pressure polymorph of ferrosilite with an orthorhombic structure. It occurs as microscopic, anhedral (irregular) grains up to 200 micrometers in size, embedded in the meteorite matrix. Due to its composition and microscopic nature, typical macroscopic specimens do not exist, and its appearance can only be assessed under a microscope. Grains typically have a dark color, ranging from dark brown to black. ## Physical Properties As a member of the pyroxene group, its hardness is estimated to be around 6 on the Mohs scale. The luster is typically vitreous. The density, calculated based on its chemical composition and unit cell parameters, is approximately 3.95 g/cm³, which is a high value resulting from its high iron content. ## Colors and Varieties Observed colors are dark brown and black. The mineral does not form color varieties or commercial varieties – it is a mineral species defined solely by its crystal structure and chemical composition. ## History and Name Hiroseite was officially approved by the International Mineralogical Association (IMA) in 2017. Its name honors Kei Hirose, a Japanese geophysicist and professor at the Tokyo Institute of Technology, for his contributions to the study of matter under conditions prevailing deep within the Earth. The mineral was discovered and identified in samples of the Suizhou meteorite, which fell in China in 1986. ## Uses Hiroseite has no commercial or industrial applications. Its significance is purely scientific, providing valuable information about processes occurring under extremely high pressure and temperature conditions, such as those found in planetary interiors or during meteorite impacts.
Diagnostic features
## Identification Identification of hiroseite is impossible without advanced analytical techniques. Due to the microscopic size of the grains and their occurrence within another rock, its recognition requires the use of an electron microscope with a microanalyzer (EDS/WDS) to determine its chemical composition, and X-ray diffraction (XRD) or electron diffraction to confirm its unique orthorhombic crystal structure. ## Distinguishing from Similar Minerals Hiroseite is a polymorph of ferrosilite and clinoferrosilite. All three have similar chemical compositions (close to FeSiO₃) but differ in crystal structure. Ferrosilite also crystallizes in the orthorhombic system, but under different pressure conditions, while clinoferrosilite crystallizes in the monoclinic system. Distinguishing them requires specialized crystallographic studies. It is distinguished from other pyroxenes in the enstatite-ferrosilite series by its almost pure iron composition. ## Crystal Forms This mineral does not form well-developed crystals. It occurs exclusively as irregular, anhedral grains within the parent rock.
Geological environment
## Genesis Hiroseite forms under conditions of extremely high pressure and temperature. Its presence in the Suizhou meteorite is the result of shock metamorphism that occurred during a cosmic collision. The impact generated pressures of about 20 GPa, leading to the phase transformation of low-pressure pyroxenes present in the meteorite into their high-pressure counterparts, such as hiroseite. ## Mineral Associations In the Suizhou meteorite, hiroseite occurs in association with other high-pressure minerals, such as ringwoodite, wadsleyite, majorite (pyroxene-rich garnet), and lingunite (a high-pressure polymorph of feldspar). It also co-occurs with olivine and low-pressure pyroxenes in less shocked parts of the meteorite. ## Localities The only confirmed locality of hiroseite in the world is the Suizhou meteorite, an L6 chondrite, which fell in 1986 in Hubei Province, China. This is its type locality.
Rarity
Extremely rare
Collector aspects
## Quality Criteria Hiroseite is not a collectible mineral in the traditional sense. It does not form aesthetic specimens, and its value is purely scientific and historical. For research institutions and specialized meteorite collectors, the value of a specimen (a thin section or meteorite fragment) lies in the confirmed presence of this extremely rare mineral, documented by appropriate analyses. ## Popular Localities The only source of hiroseite is the Suizhou meteorite. Specimens of this meteorite are very rarely available on the commercial market, and fragments containing confirmed hiroseite are mainly found in institutional and university collections.
Care and storage
## Cleaning Hiroseite specimens exist exclusively as microscopic inclusions within the parent meteorite. They do not require and are not amenable to standard cleaning. The meteorite itself, as the parent rock, should be protected from contamination and moisture. ## What to Avoid Avoid contact with chemicals, especially strong acids, which could dissolve the mineral or its surrounding matrix. The specimen (meteorite fragment) is sensitive to shocks and drops, which can cause it to fracture. Avoid abrupt temperature changes. ## Storage Meteorite fragments containing hiroseite should be stored under stable room conditions, in a dry environment, preferably in a closed box or display case, to protect them from dust and mechanical damage.