Manganosegelerite

Chemical formula: Mn<sup>2+</sup><sub>2</sub>Fe<sup>3+</sup>(PO<sub>4</sub>)<sub>2</sub>(OH)·4H<sub>2</sub>O

Manganosegelerite is a rare, hydrated manganese and iron phosphate, forming characteristic, radial aggregates of small, yellow crystals.

## Characteristics Manganosegelerite is a hydrated phosphate belonging to the segelerite group, in which manganese dominates specific positions in the crystal structure. It forms very characteristic, small aggregates, most often in the form of spherical or hemispherical clusters with a radial structure. These are composed of small, elongated, prismatic crystals. Specimens rarely exceed a few millimeters in diameter, making them primarily micro-collectible items. ## Physical Properties This mineral has a hardness of 4 on the Mohs scale, making it relatively soft and susceptible to scratching. It has a vitreous luster and is transparent to translucent. Its density is approximately 2.89 g/cm³. ## Colors and Varieties Manganosegelerite occurs in shades from light yellow, through golden yellow, to yellowish-brown and orange-brown. Its color is one of its main diagnostic features. No named varieties are distinguished. ## History and Name The name of the mineral refers to its chemical composition – the dominance of manganese (Latin: *manganum*) – and its relation to segelerite, of which it is a manganese analog. Segelerite was named after Arthur A. Segeler (1901-1989), an American mineral collector from New York who specialized in pegmatite minerals. ## Uses Due to its rarity and small crystal size, manganosegelerite has no industrial application. However, it is a valued and sought-after collector's mineral, especially among micromineral and systematic mineral collectors.

Properties

Mohs hardness
4
Luster
Vitreous
Streak
Light yellow
Density
2.89
Cleavage
Good on {010}
Fracture
Uneven
Transparency
Transparent to Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification The most important diagnostic feature of manganosegelerite is its mode of occurrence – it almost always forms spherical, radial aggregates composed of small, acicular or prismatic crystals. Its characteristic intense, yellow to orange-brown color and its occurrence environment in granitic pegmatites are also distinctive. ## Distinguishing from Similar Minerals Manganosegelerite is sometimes confused with other secondary phosphates of similar color and form. It can be distinguished from: - **Jahnsite-(CaMnMn)**: often has a more brownish or greenish hue and a slightly different crystal habit. - **Cacoxenite**: forms more fibrous, silky aggregates, with a more intense, golden-yellow color. - **Rockbridgeite**: usually has a darker, olive-green to almost black color. Definitive differentiation of these minerals often requires advanced studies, e.g., chemical analysis (EDS). ## Crystal Forms Crystals are strongly elongated, prismatic, but almost never occur as single individuals. They coalesce into characteristic, radial aggregates forming ideal spheres, hemispheres, or fan-shaped clusters on the surface of the host rock.

Geological environment

## Genesis Manganosegelerite is a secondary mineral. It forms in complex granitic pegmatites as a result of hydrothermal alteration or weathering of primary phosphate minerals, mainly from the triphylite group, such as triphylite and lithiophilite. ## Mineral Associations This mineral often co-occurs with other secondary phosphates. Its typical associated minerals include jahnsite-(CaMnMn), rockbridgeite, ludlamite, vivianite, hureaulite, as well as remnants of primary triphylite. ## Localities The most important and globally known locality for manganosegelerite, which is also its type locality, is the Tip Top mine in Custer County, South Dakota (USA). This is where the best, exemplary specimens of this mineral originate. It is also known from several other pegmatites in the Black Hills region of South Dakota.

Rarity

Very rare

For collectors

## Quality Criteria The most highly valued manganosegelerite specimens are those that exhibit perfectly formed, spherical aggregates with intense, vivid color and good luster. The completeness of the spheres and the absence of damage to the delicate crystals are important. The attractiveness of a specimen is enhanced by its placement on a contrasting rock matrix, as well as the presence of other rare phosphate minerals. ## Popular Localities By far the most sought-after specimens by collectors come from the Tip Top mine in South Dakota, USA. This locality is famous for the best-formed specimens of this mineral in the world, which serve as the standard for the species.

Care and storage

## Cleaning Manganosegelerite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Due to its low hardness, mechanical cleaning is risky. Ultrasonic cleaners are absolutely not recommended. ## What to Avoid The mineral is sensitive to high temperatures, which can lead to its dehydration (loss of water from the crystal lattice) and structural damage. Contact with acids and strong detergents should be avoided. Protect from impacts and scratching by harder minerals. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to avoid abrasions and mechanical damage. They should be protected from dust, direct sunlight, and sudden changes in temperature and humidity.

Sources

Read more