Reddingite

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

Reddingite is a hydrated manganese phosphate, forming tabular or prismatic crystals ranging in color from pink to reddish-brown.

## Characteristics Reddingite is a secondary, hydrated manganese phosphate belonging to the reddingite group. It typically forms small, well-formed crystals with a tabular, thick-tabular, or short-prismatic habit. It also occurs as granular aggregates and radial clusters. It is a brittle mineral, and its surfaces are often covered with weathering products that mask its true color and luster. ## Physical Properties The Mohs hardness of reddingite is 3.5, making it a relatively soft mineral. It exhibits a vitreous luster, transitioning to resinous on some surfaces. It is transparent to translucent. Its density ranges from 3.10-3.21 g/cm³. ## Colors and Varieties This mineral exhibits various colors—it can be colorless, yellowish-white, pink, pale pinkish-red, up to reddish-brown and brown. A characteristic feature is its tendency to darken due to manganese oxidation, so fresh, pink specimens eventually turn brown or almost black. Reddingite forms an isomorphic series with phosphoferrite (iron-rich), where it is the manganese-dominant end-member. ## History and Name Reddingite was first described in 1878 by George J. Brush and Edward S. Dana. Its name comes from the town of Redding in Fairfield County, Connecticut (USA), where its type locality is located—the famous Branchville pegmatite quarry. ## Uses Reddingite has no industrial application. It is solely an object of interest for mineral collectors and scientists studying the genesis of pegmatite deposits.

Properties

Mohs hardness
3.5
Luster
Vitreous to Resinous
Streak
White
Density
3.1-3.21
Cleavage
Good on {010}
Fracture
Uneven
Transparency
Transparent to Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Reddingite can be identified by its characteristic crystal form (short prisms and tablets in the orthorhombic system), relatively low hardness, vitreous luster, and specific occurrence environment—granitic pegmatites. Its color, ranging from pink to brown, combined with its tendency to darken, is also an important clue. ## Distinguishing from Similar Minerals Reddingite is most often confused with phosphoferrite, with which it forms a continuous series. However, phosphoferrite is an iron-dominant member and usually has a more greenish hue. A definitive distinction between these two minerals often requires chemical analysis. It can also be confused with other secondary phosphates, but it differs from them in crystal form and physical properties. ## Crystal Forms Reddingite crystals are usually small, with a thick-tabular, equant, or short-prismatic habit. They often form overgrown groups and druses. It is also found as radial or spherulitic aggregates and in granular masses intergrown with other minerals.

Geological environment

## Genesis Reddingite is a secondary mineral, forming in complex granitic pegmatites. It forms as a result of hydrothermal alteration or weathering of primary manganese- and iron-rich phosphate minerals, such as lithiophilite and triphylite. It forms under low to medium temperature conditions. ## Mineral Associations This mineral often co-occurs with other phosphates. Its most common associated minerals include: lithiophilite, triphylite, eosphorite, fairfieldite, vivianite, strengite, hureaulite, rockbridgeite, as well as quartz and feldspars. ## Localities The most important and historical occurrence is the type locality in Branchville, Connecticut, USA. Significant specimens also come from the Palermo No. 1 mine in North Groton, New Hampshire, USA, and from the Hagendorf-Süd pegmatite in Bavaria, Germany. Other known localities include pegmatites in Minas Gerais, Brazil, and Western Australia.

Rarity

Not very common

For collectors

## Quality Criteria Specimens with well-formed, sharp, and lustrous crystals of significant transparency are most highly valued by collectors. An intense, pink or reddish color is desirable, although unoxidized specimens are rare. The aesthetic composition with associated minerals, such as quartz or other rare phosphates, is also of great importance. Specimens from the type locality (Branchville) have additional historical value. ## Popular Localities The most classic and sought-after specimens come from the USA, especially from the Palermo mine in New Hampshire, which has yielded some of the world's best reddingite crystals. German Hagendorf is also a source of good quality specimens. Historical specimens from Branchville, although often small and altered, are valuable due to their scientific significance.

Care and storage

## Cleaning Reddingite specimens should be cleaned very carefully, using a soft brush and distilled water. Avoid strong rubbing due to the mineral's low hardness. The use of ultrasonic cleaners is not recommended. ## What to Avoid The mineral is susceptible to scratches. Avoid contact with harder minerals and tools. As a hydrated mineral, it is sensitive to high temperatures, which can cause dehydration and structural damage. Some specimens may darken with prolonged exposure to light and air. Avoid contact with acids and other strong chemicals. ## Storage It is recommended to store specimens in separate, padded display boxes to protect them from mechanical damage and abrasions. It is also advisable to limit exposure to intense light to slow down the darkening process.

Sources

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