Samuelsonite

Chemical formula: Ca<sub>9</sub>Mn<sup>2+</sup><sub>4</sub>Al<sub>2</sub>(PO<sub>4</sub>)<sub>10</sub>(OH)<sub>2</sub>

Samuelsonite is a very rare mineral from the phosphate group, found as small, bladed crystals in unique granitic pegmatites.

## Characteristics Samuelsonite is a complex phosphate of calcium, manganese, and aluminum. It occurs as very small, bladed or tabular crystals, usually not exceeding 1 mm in length. It forms radial aggregates or appears as single crystals embedded in other minerals. It is transparent to translucent, with a vitreous luster. ## Physical Properties The mineral is characterized by a hardness of 5 on the Mohs scale. Its density is estimated at approximately 3.43 g/cm³. It exhibits perfect cleavage in one direction. ## Colors and Varieties Samuelsonite is colorless, white, or has a pale gray hue. No varieties have been distinguished. ## History and Name The mineral was first described in 1977 by Paul B. Moore and Takaharu Araki. The name honors Peter B. Samuelson, an American mineral collector who discovered the first specimens of this mineral at the Palermo No. 1 Quarry in New Hampshire, USA. ## Uses Due to its extreme rarity and small crystal size, samuelsonite has no industrial application. It is solely an object of interest for collectors specializing in rare minerals (so-called micromounts) and scientists.

Properties

Mohs hardness
5
Luster
Vitreous
Streak
White
Density
3.43
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Amateur identification of samuelsonite is practically impossible due to its small size and similarity to other phosphates. Recognition requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS/WDS). In a collection, it can be identified based on a label from a confirmed locality. ## Distinguishing from Similar Minerals It can be confused with other rare, colorless or white phosphates found in pegmatites, such as wardite, eosphorite, or zanazziite. Differentiation without specialized equipment is impossible. Co-occurrence with other minerals from the Palermo pegmatites is key. ## Crystal Forms It forms elongated, bladed crystals with a rectangular cross-section, often flattened. They usually occur as radial or randomly oriented aggregates embedded in other minerals, mainly quartz.

Geological environment

## Genesis Samuelsonite is a hydrothermal mineral, crystallizing in the late stage of evolution of complex granitic pegmatites rich in phosphorus. It forms in rock cavities and fissures as a result of alterations of earlier phosphates. ## Mineral Associations This mineral co-occurs with other phosphates characteristic of pegmatites. At the type locality (Palermo No. 1), it was found in association with quartz, brazilianite, whitlockite, apatite, wardite, eosphorite, and zanazziite. ## Localities Samuelsonite is an extremely rare mineral, known from only a few locations worldwide. The most important and type locality is the Palermo No. 1 Quarry in North Groton, New Hampshire, USA. Its occurrence has also been confirmed in the Tip Top pegmatite in Custer County, South Dakota, USA.

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of samuelsonite primarily depends on the richness of the aggregates and the size of individual crystals, although these rarely exceed a millimeter. Specimens with well-formed, radial aggregates on a contrasting matrix, e.g., in quartz druses, are highly valued. Association with other rare phosphates is also important. ## Popular Localities By far the most valued and known specimens come from the discovery site – the Palermo No. 1 Quarry in New Hampshire, USA. This is the classic and most important locality for this mineral.

Care and storage

## Cleaning Samuelsonite specimens should be cleaned very carefully, preferably using compressed air to remove dust. Contact with water is not recommended, especially if the mineral occurs on a sensitive matrix. If necessary, a soft brush can be used. ## What to Avoid Avoid contact with all chemicals, acids, and detergents. The mineral is sensitive to ultrasound, which can damage delicate crystals. It should not be heated or exposed to sudden temperature changes. ## Storage Samuelsonite collections, usually in the form of micromounts, should be stored in closed, stable boxes that protect against dust, moisture, and mechanical damage. Due to the small size of the crystals, proper labeling of the container is crucial.

External references

Sources

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