Landesite
Chemical formula: Mn²⁺₉Fe³⁺₃(PO₄)₈(OH)₃(H₂O)₉
A rare manganese and iron phosphate, found in granitic pegmatites as an alteration product of other phosphate minerals.
Properties
- Mohs hardness
- 3-3.5
- Color
- red brown; yellowish brown in transmitted light
- Luster
- Vitreous to Resinous
- Streak
- Yellow-brown
- Density
- 3.026
- Cleavage
- On {010}, perfect; one poor at right angles to the perfect cleavage.
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Landesite is identified by its characteristic habit of small, tabular crystals forming rosetted aggregates, brown color, and occurrence in granitic pegmatites. Identification usually requires magnification and often advanced research methods, such as chemical analysis (EDS) or X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other brown phosphate minerals found in pegmatites, such as strengite, rockbridgeite, or stewartite. Distinguishing it from these minerals based on visual characteristics is very difficult and usually requires laboratory analysis. Landesite often forms pseudomorphs after other minerals, which further complicates identification. ## Crystal Forms It forms thin, tabular crystals with a hexagonal or octagonal outline. These crystals often group into radial, rosetted, or spherulitic aggregates. It also occurs as granular aggregates and as pseudomorphs after other minerals, e.g., reddingite.
Geological environment
## Genesis Landesite is a secondary phosphate mineral, formed in oxidation zones and by hydrothermal alteration in granitic pegmatite deposits. It forms as a result of the alteration of primary manganese and iron phosphates, such as reddingite, under low-temperature conditions. ## Mineral Associations It often co-occurs with minerals from which it forms or which accompany it during alteration. Typical associated minerals include reddingite, strengite, rockbridgeite, stewartite, hureaulite, phosphosiderite, as well as quartz, muscovite, and other pegmatite minerals. ## Localities The most important landesite localities worldwide are pegmatites in South Dakota (USA), especially in the Keystone and Custer area (e.g., Tip Top mine, Bull Moose). It is also found in New Ross, Nova Scotia (Canada - type locality), in the Hagendorf-Süd pegmatites in Bavaria (Germany), and in Mangualde (Portugal).
Rarity
Rare
For collectors
## Quality Criteria Specimens with well-formed, sharp crystals forming aesthetic, rosetted aggregates are most valued by collectors. The contrasting color of the host rock matrix, which highlights the brown color of landesite, is important. Due to its rarity, even microscopic but well-defined crystals are valuable. Specimens from historical localities, such as South Dakota, are particularly sought after. ## Popular Localities Collectors most highly value specimens from classic localities in South Dakota, USA (Tip Top, Bull Moose, White Elephant mines), which have yielded the best known crystals of this mineral.
Care and storage
## Cleaning Due to its fragility and small crystal size, mechanical cleaning is not recommended. Compressed air can be used to remove dust. Any wet cleaning should be performed with the utmost caution, using only distilled water and without immersing the specimen. ## What to Avoid Avoid contact with acids and other chemicals that may damage the mineral. Landesite is sensitive to high temperatures, which can lead to its dehydration and destruction. It should be protected from ultrasound and vibrations. ## Storage Landesite specimens, especially micromounts, are best stored in enclosed, padded boxes to protect them from dust, mechanical damage, and sudden changes in humidity.