Ramsdellite

Chemical formula: Mn<sup>4+</sup>O<sub>2</sub>

A rare manganese oxide mineral, a polymorphic variety of pyrolusite, forming black, fibrous or radiating aggregates.

## Characteristics Ramsdellite is a manganese(IV) oxide and one of the polymorphic varieties of the mineral pyrolusite. It occurs much less frequently than pyrolusite. It usually forms fibrous, radiating, reniform, or massive aggregates. Well-formed crystals are rare and typically appear as small, prismatic columns with striated surfaces. The mineral has a black color and a metallic luster. ## Physical Properties Its Mohs hardness is approximately 3. It is a brittle mineral with a density of about 4.7 g/cm³. It exhibits distinct cleavage in two directions. The luster is metallic, becoming dull on weathered surfaces. It is opaque. ## Colors and Varieties This mineral is always black or steel-gray. No color or commercial varieties are distinguished. It often occurs in intimate intergrowth with other manganese oxides, especially pyrolusite and hollandite, which can make identification difficult without advanced studies. ## History and Name The name ramsdellite was given in honor of Lewis S. Ramsdell (1895–1975), an American mineralogist and crystallographer from the University of Michigan, who first thoroughly studied and described this crystalline phase of manganese oxide in 1932. The mineral was formally described and named by Michael Fleischer and Wallace E. Richmond in 1943 based on material from Lake Valley, New Mexico, USA. ## Uses Due to its rarity, ramsdellite has no industrial significance as a manganese ore. However, it is an interesting object for advanced systematic mineral collectors and scientific institutions studying the mineralogy of manganese oxides.

Properties

Mohs hardness
3
Luster
Metallic
Streak
Black
Density
4.65-4.83
Cleavage
Perfect on {010}, good on {110}
Fracture
Uneven
Transparency
Opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Characteristic features of ramsdellite include its black color, metallic luster, and typical forms of occurrence – fibrous or radiating aggregates. The streak on an unglazed porcelain plate is black or brownish-black. Compared to massive pyrolusite, ramsdellite more often forms aggregates with a distinct internal structure. ## Distinguishing from Similar Minerals The most difficult task is distinguishing ramsdellite from pyrolusite (its polymorph). Both have identical chemical compositions, black color, and streak. However, pyrolusite is more common, crystallizes in the tetragonal system, and often forms dendrites or acicular aggregates. Certain differentiation of these two minerals is almost exclusively possible using X-ray diffraction (XRD) methods. It can also be confused with other black manganese oxides, such as hollandite, cryptomelane, or goethite, from which it differs in crystal form (if present) and physical properties, but certain identification often requires laboratory analysis. ## Crystal Forms Ramsdellite crystallizes in the orthorhombic system. Well-formed crystals are rare, usually appearing as short, prismatic columns, often with longitudinal striations on the faces. It is most commonly found in the form of fibrous, radiating, reniform aggregates, as well as compact and earthy masses.

Geological environment

## Genesis Ramsdellite is a secondary mineral, forming in the oxidation zones of manganese ore deposits. It forms under low temperature and pressure conditions, often as a result of the weathering of other manganese minerals, such as hausmannite or rhodochrosite. It can also form in bog and lake sediments rich in manganese. ## Mineral Associations It most often co-occurs with other manganese oxides, with which it is closely related genetically and chemically. Its typical associated minerals include pyrolusite, hollandite, cryptomelane, goethite, as well as calcite and quartz. ## Localities Among the most important and classic localities for ramsdellite are Lake Valley in Sierra County, New Mexico (USA), where it was first thoroughly described. Other known occurrences include Butte, Montana (USA), the Mistake Mine in Arizona (USA), and Třebíč in the Czech Republic. Occurrences have also been reported in Germany (Ilfeld, Harz), India, Japan, and Mexico.

Rarity

Rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, visible crystals, which is a great rarity for this mineral. Rich, radiating aggregates with a distinct structure and intense, metallic luster are also highly prized. A well-documented locality is also important, especially if it is a type locality – Lake Valley. The purity of the specimen and the absence of mechanical damage significantly increase its value. ## Popular Localities Specimens from Lake Valley, New Mexico, and the Mistake Mine in Arizona, USA, are considered classic and most sought after by collectors specializing in systematic minerals.

Care and storage

## Cleaning Ramsdellite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its brittleness and the possible presence of loose fibers, avoid washing under running water. If it is necessary to remove dirt, a damp cloth or cotton swab can be used to gently wipe the surface. ## What to Avoid Avoid contact with acids and other strong chemicals that may react with manganese oxides. The mineral is brittle, so it must be protected from impacts, drops, and vibrations. It should not be heated or exposed to sudden temperature changes. ## Storage It is recommended to store specimens in separate, padded collector boxes to prevent abrasion and mechanical damage. Protect it from dust, which can accumulate in porous aggregates and be difficult to remove. Display should be in stable conditions, away from direct sunlight and sources of moisture.

External references

Sources

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