Laihunite

Chemical formula: (Fe<sup>3+</sup>,Fe<sup>2+</sup>,&#9744;)<sub>2</sub>SiO<sub>4</sub>

Laihunite is a rare iron silicate, related to olivine, formed by the oxidation of fayalite and characterized by a dark, almost black color.

## Characteristics Laihunite is an iron silicate, closely related to the much more common fayalite (an iron-rich variety of olivine). It most often forms granular or massive aggregates, ranging in color from brownish-black to black. It rarely occurs as well-formed crystals, and its specimens usually appear as irregular grains embedded in the host rock. It is an opaque mineral, with a characteristic, slightly greasy or submetallic luster. ## Physical Properties Its Mohs hardness is about 6, which makes it a relatively hard mineral. It is distinguished by a significant density, ranging from 4.1-4.3 g/cm³, which is noticeable when compared to minerals of similar volume. The luster is most often greasy, transitioning to submetallic. It is a brittle mineral. ## Colors and Varieties Laihunite is uniform in color – it occurs in shades from dark brown to black. No color varieties or commercial varieties are distinguished. ## History and Name The mineral's name comes from its discovery locality – the Laihe (in older transcription Laihun) iron ore deposit in Liaoning Province, China. It was first described as a new mineral species in 1976 by a Chinese research group. Its status as a distinct mineral was debated but was ultimately approved by the International Mineralogical Association (IMA). ## Applications Laihunite has no industrial application. Due to its rarity and specific origin, it is a mineral of interest mainly to scientists and advanced collectors of systematic minerals.

Properties

Mohs hardness
6
Luster
Greasy to submetallic
Streak
Brownish black
Density
4.1-4.3
Cleavage
Poor on {010}
Fracture
Uneven to subconchoidal
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Features facilitating the identification of laihunite include its high density, black or brownish-black color, greasy or submetallic luster, and hardness (approx. 6 on the Mohs scale). A key indicator is its co-occurrence with fayalite, often in the form of its alteration products. ## Distinguishing from Similar Minerals - **Fayalite**: Laihunite is harder and denser than fayalite. Laihunite often forms veins or rims around fayalite relics, which may have a more greenish or brownish hue. - **Magnetite**: Laihunite does not exhibit magnetic properties or they are very weak, unlike strongly magnetic magnetite. Magnetite also usually has a more metallic luster. - **Ilmenite**: Ilmenite has a more distinct metallic luster and a different crystal structure. The streak of ilmenite is black to brownish-red. ## Crystal Forms Well-formed crystals are extremely rare. Laihunite almost always occurs as anhedral (irregular) grains, granular aggregates, or in massive forms.

Geological environment

## Genesis Laihunite is a secondary mineral, formed by the oxidation and dehydration processes of iron-rich olivine (fayalite). It forms under conditions of low-temperature metamorphism or during the weathering of igneous rocks containing fayalite. It is a typical component of some metamorphosed iron formations. ## Mineral Associations It most often co-occurs with its parent mineral – fayalite. It is also accompanied by magnetite, quartz, hematite, and amphiboles from the cummingtonite-grunerite group. ## Localities The most important and classic occurrence is the type locality – the Laihe deposit in Liaoning Province, China. It has also been reported in other iron formations worldwide, including the Mesabi Range area in Minnesota (USA) and in some meteorites as a product of fayalite alteration.

Rarity

Very rare

For collectors

## Quality Criteria The quality of laihunite specimens is primarily assessed based on its proportion in the sample mass and the confirmation of its identity. Since it does not form aesthetic crystals, rich aggregates where the mineral is clearly visible are most valued. An additional value is a clear association with relict fayalite, illustrating its formation process. ## Popular Localities Specimens from the type locality in China (Laihe) are by far the most valued and sought after by collectors. Material from other localities is rarely available on the collector's market and is mainly of scientific importance.

Care and storage

## Cleaning Laihunite specimens are best cleaned dry using a soft brush. If necessary, distilled water can be used, and then the specimen should be thoroughly dried. Ultrasonic cleaners should be avoided, as they can cause cracks in the brittle mineral grains. ## What to Avoid The mineral should be protected from contact with strong acids and other aggressive chemicals. As an oxidation product, it is relatively stable, but prolonged exposure to high humidity is recommended to be avoided. ## Storage Store in a dry place, preferably in a closed display box, to protect it from dust and scratches from harder minerals. It does not require special lighting conditions.

Sources

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