Lipscombite

Chemical formula: Fe²⁺Fe³⁺₂(PO₄)₂(OH)₂

Lipscombite is a rare phosphate mineral, forming tiny, tetragonal crystals ranging in color from olive-green to black.

## Characteristics Lipscombite is a hydrated iron phosphate, belonging to the group of rare secondary minerals. It typically occurs as very small, lustrous crystals with a bipyramidal habit or in granular, rosette-like aggregates, as well as coatings and efflorescences. Its color is variable, most commonly dark green, olive-green, to almost black specimens are found. Less frequently, it takes on greenish or yellowish-brown hues, which is related to the oxidation state of iron in its structure. ## Physical Properties Lipscombite crystals exhibit a luster ranging from vitreous to almost metallic. The mineral is usually opaque, although very thin fragments can be translucent or even transparent. Its hardness on the Mohs scale is approximately 4.5-5, and its density is 3.66 g/cm³. ## Colors and Varieties The dominant colors are dark shades of green, from olive to blackish-green. Black specimens are also found, and weathering can lead to lighter, greenish or yellowish-brown coatings. No named varieties of this mineral are distinguished. ## History and Name The mineral was first described in 1953 by John W. Gruner. The name "lipscombite" honors William Lipscomb (1919-2011), a professor of chemistry at the University of Minnesota and later a Nobel laureate in chemistry (1976), for his work on the structure of boranes. ## Uses Lipscombite has no industrial application. It is solely an object of interest for collectors specializing in rare phosphate minerals and systematic mineralogists.

Properties

Mohs hardness: 4.5-5
Luster: Vitreous to metallic
Streak: Greenish-black
Density: 3.66
Cleavage: Imperfect on {001}
Fracture: Uneven
Transparency: Transparent,Translucent,Opaque
Crystal system: Tetragonal

Diagnostic features

## Identification Lipscombite is recognized by its characteristic, small, lustrous crystals with a tetragonal shape, often forming rosette-like or granular aggregates. Key features include its dark green to black color, vitreous luster, and occurrence in the oxidation zones of phosphate pegmatites. ## Distinguishing from Similar Minerals It can be confused with other dark secondary minerals such as rockbridgeite, strengite, or cacoxenite. It differs from rockbridgeite in crystal habit (rockbridgeite forms fibrous or radial aggregates). Distinguishing it from other microcrystalline phosphates often requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms It forms very small, dipyramidal crystals with a square cross-section. Most often, it occurs as granular, spherulitic, rosette-like aggregates or as thin coatings and efflorescences on other minerals.

Geological environment

## Genesis Lipscombite is a secondary mineral, formed as a result of hydrothermal alteration or weathering of primary phosphate minerals (mainly triphylite) in granite pegmatites rich in phosphorus. It forms in oxidation zones where the valence of iron changes. ## Mineral Associations It often co-occurs with minerals from which it forms or which accompany it during weathering. Typical associated minerals include triphylite, heterosite, rockbridgeite, strengite, cyrilovite, leucophosphite, as well as quartz, muscovite, and other pegmatite minerals. ## Localities The most important and type locality is the Sapucaia mine in Minas Gerais, Brazil. It is also known from several localities in the USA, including the Palermo and Fletcher mines in New Hampshire, the Foote mine in North Carolina, and the Black Hills in South Dakota. Its presence has also been confirmed in Spain and Germany.

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, though usually microscopic, crystals with a distinct luster and intense, dark green color. Contrastive placement on a light rock matrix, such as quartz or feldspar, enhances its attractiveness. Large, rich aggregates of rosettes or coatings are also sought after. ## Popular Localities Specimens from the type locality, the Sapucaia mine in Brazil, are considered classic and most desirable. Well-crystallized microcrystals from pegmatites in New Hampshire (USA) are also highly valued.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft brush to remove dust. The use of water is not recommended, as the mineral may be sensitive to moisture and react with it, especially if it contains admixtures of other soluble minerals. ## What to Avoid Contact with acids and other chemicals that can destroy the mineral should be strictly avoided. Lipscombite is sensitive to changes in humidity and temperature. It should not be heated or exposed to prolonged intense sunlight. ## Storage It is recommended to store specimens in stable conditions, preferably in sealed, dry containers or display boxes, away from sources of moisture and direct light. Due to the small size of the crystals, "micromount" boxes are ideal.