Philipsbornite

Chemical formula: Pb₂+Al₃(As₅+O₄)(As₅+O₃OH)(OH)₆

Philipsbornite is a rare lead-aluminum arsenate, forming tiny, white or colorless crystals, prized by collectors of rare minerals.

## Characteristics Philipsbornite is a rare mineral from the arsenate group, belonging to the crandallite group. It occurs as very small, tabular or pseudocubic crystals, often forming rosette-like aggregates or crusty coatings. Individual crystals rarely exceed 0.5 mm in size. It is a secondary mineral, formed in the oxidation zones of ore deposits. ## Physical Properties Philipsbornite crystals exhibit a hardness of approximately 4.5 on the Mohs scale. They have a vitreous to dull luster, and their density is about 4.15 g/cm³. They are brittle and translucent to opaque. ## Colors and Varieties This mineral is typically colorless, white, or pale yellow. No distinct color varieties or commercial varieties are recognized. ## History and Name Philipsbornite was first described in 1982 by P.J. Dunn, P.J. Sturman, and J.A. Nelen. The mineral is named in honor of Professor Helmuth von Philipsborn (1892-1983), a German mineralogist and crystallographer from the University of Regensburg, for his contributions to ore mineralogy. ## Uses Due to its rarity and small crystal size, philipsbornite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or micromounts.

Properties

Mohs hardness: 4.5
Luster: Vitreous
Streak: White
Density: 4.15
Cleavage: Good on {0001}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Trigonal

Diagnostic features

## Identification Amateur identification of philipsbornite is practically impossible due to the microscopic size of the crystals and their resemblance to many other secondary arsenate minerals. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS/WDS). ## Distinguishing from Similar Minerals Philipsbornite is visually indistinguishable from other minerals of the crandallite group, such as hidalgoite, hinsdalite, or segnitite, with which it often co-occurs and forms solid solutions. Differentiation is possible only through chemical analysis. ## Crystal Forms It forms tiny, tabular crystals with trigonal or hexagonal outlines, as well as pseudocubic (rhombohedral) crystals. These crystals often combine into rosette-like or spherulitic aggregates and form thin crusts and coatings.

Geological environment

## Genesis Philipsbornite is a secondary mineral, formed in the oxidation zones (so-called iron caps) of polymetallic deposits rich in arsenic and lead. It forms as a result of the weathering of primary sulfides and arsenides. ## Mineral Associations It most commonly co-occurs with other secondary arsenates and sulfates, such as segnitite, hidalgoite, beudantite, anglesite, cerussite, mimetite, pharmacosiderite, as well as with quartz, goethite, and hematite. ## Localities Key localities worldwide include the Tsumeb mine in Namibia (where it was discovered), Dundas in Tasmania (Australia), the Clara mine in the Black Forest (Germany), and deposits in the Atacama region of Chile. It also occurs in many other places worldwide as an accessory mineral.

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of philipsbornite primarily depends on the quality of the locality and associated minerals. The most prized specimens are those with well-formed, though still microscopic, crystals forming aesthetic groups on a contrasting matrix. Due to its microscopic nature, specimens are almost exclusively the domain of collectors specializing in micromounts. ## Popular Localities Specimens from the Tsumeb mine in Namibia and from Dundas in Tasmania are considered classic and most sought after by collectors.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Due to their fragility and small crystal size, wet cleaning or ultrasonic cleaning is not recommended. ## What to Avoid Avoid contact with acids and other chemicals that can damage the mineral. Crystals are brittle, so they should be protected from impacts and vibrations. ## Storage It is recommended to store specimens in specialized "micromount" boxes, which protect delicate crystals from mechanical damage and dust. Avoid exposure to extreme temperatures and humidity.

Sources

IMA Mineral List (CNMNC)