Yuanfuliite

Chemical formula: Mg(Fe<sup>3+</sup>,Al)O(BO<sub>3</sub>)

A very rare magnesium and iron borate, forming hard, black, and lustrous crystals in skarns.

## Characteristics Yuanfuliite is a mineral from the borate group, chemically classified as a magnesium and iron oxyborate (with a possible admixture of aluminum). It typically forms well-developed, prismatic or tabular crystals of a black, less commonly brownish-black color. Their surface is characterized by a strong, almost adamantine luster. Specimens most often occur as single crystals embedded in rock or small aggregates thereof. ## Physical Properties This mineral is characterized by high hardness, measuring 7.5 on the Mohs scale, which makes it scratch-resistant. It has a relatively high density, about 3.92 g/cm³. It is opaque, and its luster is described as vitreous to subadamantine. It exhibits distinct cleavage in two directions. ## Colors and Varieties The dominant and essentially only color of yuanfuliite encountered is black. Shades of very dark brown are observed less frequently. No color or commercial varieties are distinguished. ## History and Name The mineral's name, approved by the International Mineralogical Association (IMA) in 1994, honors the Chinese geologist and discoverer, Professor Yuan Fuli (1893–1987). It was first described from the boron-rich Zhuanmiao deposit in Liaoning Province, China, which is its type locality. ## Uses Due to its extreme rarity, yuanfuliite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced collections of rare and systematic minerals.

Properties

Mohs hardness
7.5
Luster
Vitreous, Sub-Adamantine
Streak
Light brown
Density
3.92
Cleavage
Good on {100} and {010}
Fracture
Uneven
Transparency
Opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Characteristic features of yuanfuliite include its black color, high hardness (7.5 on the Mohs scale), strong luster, and specific occurrence environment (boron skarns). Crystals often have the form of elongated prisms. ## Distinguishing from Similar Minerals It can be confused with black tourmaline (schorl), which, however, crystallizes in the trigonal system and often has visible striations on the prism faces. It can also resemble minerals from the ludwigite-vonsenite group, which typically form fibrous or acicular aggregates and have lower hardness. Definitive differentiation often requires advanced studies, e.g., chemical analysis. ## Crystal Forms It crystallizes in the orthorhombic system. It forms columnar, prismatic, or tabular crystals, often elongated along one axis. It also occurs as granular aggregates in the host rock.

Geological environment

## Genesis Yuanfuliite is a mineral of metamorphic origin. It forms under conditions of high-temperature contact metamorphism, in boron-rich zones, referred to as magnesian skarns. It forms at the contact of magmatic intrusions with carbonate rocks, mainly dolomites. ## Mineral Associations It most often co-occurs with other rare borates, such as suanite and szaibelyite, as well as sinhalite, forsterite, phlogopite, spinel, and magnetite. ## Localities The most important and type locality is the Zhuanmiao boron deposit in Liaoning Province, China. It is also known from genetically similar deposits, such as Titovskoe on the Kola Peninsula in Russia and from Sierra de Baza in Spain.

Rarity

Very rare

For collectors

## Quality Criteria The most highly valued specimens are those with sharply terminated, well-formed, and highly lustrous crystals. The size of the crystals is of great importance, as most of them are small (a few millimeters). The attractiveness of a specimen is significantly enhanced by its occurrence on a light rock matrix or in association with other rare accessory minerals, e.g., suanite. ## Popular Localities By far the best and most sought-after specimens come from the type locality in China (Zhuanmiao, Liaoning). Material from Russia is also known but less commonly found on the collector's market.

Care and storage

## Cleaning Specimens should be cleaned very carefully, preferably dry, using a soft brush to remove dust. In case of heavier soiling, brief cleaning in distilled water with a soft brush is permissible. After contact with water, the specimen should be immediately and thoroughly dried. ## What to Avoid Ultrasonic cleaners, strong detergents, acids, and organic solvents should be strictly avoided. The mineral is sensitive to sudden temperature changes. It should not be exposed to prolonged direct sunlight. ## Storage It is recommended to store in stable room conditions, away from sources of moisture and contaminants. The safest method is to keep the specimen in a separate, padded display box to avoid the risk of mechanical damage.

External references

Sources

Read more