Jianshuiite

Chemical formula: MgMn₄+₃O₇·₃H₂O

Jianshuiite is a rare hydrated magnesium manganese oxide, forming characteristic black, fibrous or spherulitic aggregates.

## Characteristics Jianshuiite is a mineral from the oxide group, visually presenting as aggregates of black, opaque crystals. It most often forms fibrous, radial, or spherulitic (spherical) aggregates. The individual "fibers" in these aggregates are actually elongated, platy crystals. Due to its structure and composition, it is classified as a mineral of the todorokite group. ## Physical Properties This mineral is characterized by a metallic to submetallic luster. It is relatively soft, with a Mohs hardness of approximately 2. It is opaque, and its density, calculated based on the chemical formula and cell parameters, is about 3.35 g/cm³. ## Colors and Varieties Jianshuiite occurs in a uniform, black color. No color varieties or commercial varieties are distinguished. ## History and Name The mineral's name comes from its discovery and first description locality – the Laochang manganese mine in Jianshui County, Honghe Prefecture, Yunnan Province, China. It was approved as a new mineral species by the International Mineralogical Association (IMA) in 1990. ## Uses Jianshuiite has no industrial applications. Its significance is limited to scientific and collecting interest, as a rare and well-defined representative of manganese oxides.

Properties

Mohs hardness: 2
Luster: Metallic
Streak: Black
Density: 3.35
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Key diagnostic features of jianshuiite include its black color, metallic luster, and characteristic occurrence in the form of radial, fibrous, or spherulitic aggregates. A black streak is also an important indicator. ## Distinguishing from Similar Minerals Jianshuiite can be confused with other black manganese oxides, such as pyrolusite, hollandite, cryptomelane, or todorokite. It differs from pyrolusite by its slightly lower hardness and lack of tendency to stain hands. Distinguishing it from other minerals in this group (so-called "black manganese minerals") based on visual features is often impossible and requires advanced analyses, e.g., X-ray diffraction (XRD). ## Crystal Forms This mineral forms microscopic, platy crystals that combine into characteristic aggregates. Most commonly observed are radial-fibrous forms, spherical aggregates (spherulites), and rosette aggregates.

Geological environment

## Genesis Jianshuiite is a secondary mineral, forming in the oxidation (weathering) zones of manganese ore deposits. It forms as a result of hydrothermal or weathering processes acting on earlier manganese minerals in a magnesium-rich environment. ## Mineral Associations This mineral often co-occurs with other manganese oxides, such as todorokite, birnessite, cryptomelane, as well as with calcite, dolomite, and quartz. ## Localities The most important and classic occurrence of jianshuiite is its type locality – the Laochang manganese mine in Jianshui County, China. It has also been identified in several other locations worldwide, including manganese ore mines in the Republic of South Africa (e.g., in the Kuruman area of the Kalahari Desert).

Rarity

Rare

For collectors

## Quality Criteria The most valuable jianshuiite specimens are characterized by well-formed, distinct spherulitic or radial aggregates with an intense luster. The absence of damage to delicate structures and aesthetic placement on the rock matrix are important. Contrast with a light-colored matrix mineral (e.g., calcite) can enhance the specimen's attractiveness. ## Popular Localities Specimens from the type locality in Laochang, China, are by far the most valued and sought after by collectors. They are considered classic for this mineral.

Care and storage

## Cleaning Jianshuiite specimens should only be dry-cleaned, using a soft brush or compressed air to remove dust. Avoid contact with water, which can react with the mineral or weaken its structure. ## What to Avoid Absolutely avoid contact with water, acids, and other chemicals. The mineral is soft and brittle, so it must be protected from impacts, scratches, and vibrations. It should not be subjected to ultrasonic cleaning. ## Storage It is recommended to store specimens in stable, closed collector's boxes that protect against dust, humidity, and mechanical damage. Avoid places with high air humidity.

Sources

IMA Mineral List (CNMNC)