Zhanghengite

Chemical formula: CuZn

Zhanghengite is a naturally occurring copper-zinc alloy (brass), originally discovered in a meteorite.

## Characteristics Zhanghengite is a mineral from the native elements group, a natural alloy of copper and zinc, making it the natural equivalent of brass. It typically forms very fine, irregular grains or lamellae with a metallic appearance, most often embedded in the matrix of other meteoritic minerals. Its identification is almost exclusively possible using advanced analytical techniques, such as electron microprobe analysis, due to the microscopic size of its grains. ## Physical Properties This mineral is characterized by a metallic luster and is opaque. Its Mohs hardness is approximately 4, and its density is high, estimated at 7.65 g/cm³. It is malleable and ductile, similar to synthetic brass. ## Colors and Varieties Zhanghengite ranges in color from golden-yellow to coppery-red, depending on the precise ratio of copper to zinc. No varieties of zhanghengite are distinguished. ## History and Name The mineral was first identified in 1985 in the Boxian chondrite meteorite, which fell in 1977 in Anhui Province, China. Its name honors Zhang Heng (78-139 AD), a prominent Chinese astronomer, mathematician, and inventor from the Han Dynasty, credited with inventing the first seismoscope. ## Uses Zhanghengite has no industrial application due to its extreme rarity and microscopic size. Its significance is purely scientific and collectible, especially for collectors specializing in meteoritic minerals.

Properties

Mohs hardness: 5
Color: Golden-yellow
Luster: Metallic
Streak: Bronze
Density: 0
Cleavage: None
Fracture: Hackly
Transparency: Opaque
Crystal system: Isometric

Diagnostic features

## Identification Identifying zhanghengite in the field or in a collection is impossible without specialized laboratory equipment. Identification requires chemical composition analysis (EDS/WDS) and crystal structure analysis (XRD) on polished meteorite sections. Its golden-yellow color in reflected light is an indication but not a diagnostic feature. ## Distinguishing from Similar Minerals At the microscopic level, it can be confused with other natural alloys, such as aurichalcite (brass of a different composition) or danbaite. Differentiation requires precise analysis of the Cu to Zn ratio. It differs from native copper in color (it is more yellow than red). ## Crystal Forms Zhanghengite occurs as anhedral (irregular) grains and lamellae, typically not exceeding 0.1 mm in size. It rarely forms poorly developed, cubic crystals.

Geological environment

## Genesis Zhanghengite is an extraterrestrial mineral. It forms under specific reducing conditions during metamorphic or shock processes occurring within the parent bodies of asteroids from which meteorites originate. Its presence indicates an oxygen- and sulfur-poor environment. ## Mineral Associations This mineral co-occurs with other minerals typical of meteorites, such as kamacite, taenite, troilite, schreibersite, as well as olivine and pyroxene in the chondritic matrix. ## Localities Confirmed occurrences of zhanghengite are limited to a few meteorites. Besides the type locality in the Boxian meteorite (Anhui, China), it has also been identified in the Allende meteorite (Mexico) and in cosmic dust samples collected in the stratosphere.

Rarity

Extremely rare

For collectors

## Quality Criteria Since zhanghengite is a microscopic mineral, it is not evaluated in terms typical for collectible specimens (luster, form, purity). Its collectible value lies in the mere fact of possessing a meteorite fragment in which the presence of this rare mineral has been confirmed. The value of the specimen is therefore the value of the meteorite itself, rather than zhanghengite as such. ## Popular Localities The only source of specimens are the meteorites in which it has been identified, primarily Boxian and Allende. Fragments of these meteorites are available on the collector's market, but zhanghengite is not visible to the naked eye within them.

Care and storage

## Cleaning Specimens containing zhanghengite (usually meteorite fragments) should not be wet-cleaned. Dust should only be removed with a soft brush or compressed air from a safe distance. ## What to Avoid Contact with water, chemicals, acids, and bases must be strictly avoided, as they can quickly damage this metallic mineral. High humidity leads to oxidation and corrosion. It should be protected from temperature changes and direct sunlight. ## Storage Meteorite fragments with zhanghengite should be stored in dry, stable conditions. The best solution is airtight containers (e.g., membrane boxes) with a desiccant (e.g., silica gel) to prevent oxidation.