Segelerite

Chemical formula: CaMgFe₃+(PO₄)₂(OH)·₄H₂O

Segelerite is a rare, hydrated calcium, magnesium, and iron phosphate, forming small, vitreous crystals with a characteristic yellowish-green color.

## Characteristics Segelerite is a mineral from the phosphate group, chemically classified as a hydrated calcium, magnesium, and iron phosphate. It occurs as small, tabular or prismatic crystals, rarely exceeding a few millimeters in length. It typically forms radial aggregates, rosettes, or occurs as crusts. Its most distinctive feature is its intense yellowish-green to olive-green color. ## Physical Properties This mineral is characterized by a vitreous luster and is transparent to translucent. Its Mohs hardness is 4, classifying it as a relatively soft mineral. The density of segelerite is calculated to be 2.78 g/cm³. ## Colors and Varieties Segelerite occurs in shades from yellowish-green to olive-green. No distinct color varieties or commercial varieties have been identified. ## History and Name The mineral's name honors Curt G. Segeler (1901-1989), an American chemist and amateur mineralogist from Brooklyn, New York, who specialized in minerals of the apatite group. Segelerite was first described in 1974 based on material from the Tip Top mine in Custer County, South Dakota, USA. ## Applications Segelerite has no industrial applications. Its significance is purely scientific and as a collector's item, being a prized micromineral due to its rarity and attractive crystal forms.

Properties

Mohs hardness: 4
Luster: Vitreous
Streak: Pale greenish yellow
Density: 2.78
Cleavage: Good on {010}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Segelerite can be identified by its characteristic yellowish-green color, vitreous luster, and typical forms of occurrence – radial aggregates and small, tabular crystals. Its geological environment is also key – zones of hydrothermal alteration in granitic pegmatites. ## Distinguishing from Similar Minerals It can be confused with other secondary phosphates of similar color, such as rockbridgeite, strengite, or phosphosiderite. Distinguishing it often requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS). The mineralogical context and co-occurrence with other pegmatite phosphates (e.g., jahnsite, ludlamite) are important diagnostic clues. ## Crystal Forms Segelerite crystals are usually small, tabular, flattened parallel to {010}, or short-prismatic. They most often form fan-shaped and radial aggregates, as well as spherical clusters and crusts on other minerals.

Geological environment

## Genesis Segelerite is a secondary phosphate mineral that forms as a result of hydrothermal processes or weathering in complex granitic pegmatites. It forms in rock cavities and fissures through the alteration of primary phosphates, such as triplite. ## Mineral Associations This mineral co-occurs with other phosphates, which is typical for its genetic environment. The most common associated minerals include: jahnsite-(CaMnMg), rockbridgeite, ludlamite, strengite, phosphosiderite, triplite, pyrite, and quartz. ## Localities The most important and type locality for segelerite is the Tip Top mine in Custer County, South Dakota, USA, from which the best-known specimens originate. It is also known from several other pegmatites worldwide, including the Palermo No. 1 mine in Grafton County, New Hampshire, USA, and from rare occurrences in pegmatites in Hagendorf, Bavaria, Germany.

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp crystals forming aesthetic, radial aggregates. An intense, pure, yellowish-green color without brown tarnish is highly valued. A contrasting combination with a white rock matrix or other well-formed associated minerals (e.g., ludlamite) significantly increases the specimen's value. Due to the small size of its crystals, segelerite is primarily of interest to micromineral collectors. ## Popular Localities By far the most desirable and classic locality for segelerite is the Tip Top mine in South Dakota, USA. Specimens from this location are considered exemplary for this mineral species.

Care and storage

## Cleaning Segelerite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its softness and potential reactivity, washing in water should be avoided, especially the use of ultrasonics, which can damage delicate crystals. ## What to Avoid Contact with acids and other chemicals should be avoided. As a hydrated mineral, it can be sensitive to high temperatures, which can lead to dehydration and structural damage. It should also be protected from mechanical damage and scratching. ## Storage Collector's specimens of segelerite, especially microminerals, are best stored in sealed "micromount" boxes, which protect them from dust, moisture, and physical damage. Exposure to direct sunlight and extreme temperature fluctuations should be avoided.