Morelandite
Chemical formula: Ca<sub>2</sub>Ba<sub>3</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>3</sub>Cl
A very rare calcium barium arsenate of the apatite group, occurring as small, hexagonal crystals.
Properties
- Mohs hardness
- 4.5
- Luster
- Vitreous to resinous
- Streak
- White
- Density
- 4.9-4.98
- Cleavage
- Indistinct on {0001}
- Fracture
- Conchoidal to uneven
- Transparency
- Transparent to translucent
- Crystal system
- Hexagonal
Diagnostic features
## Identification Identifying morelandite is difficult. Key diagnostic features include: high density (easily felt in hand even with a small specimen), hexagonal crystal form (if visible), and occurrence in a specific geological environment. Positive identification almost always requires advanced analytical methods, such as energy-dispersive spectroscopy (EDS) or X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Morelandite is visually almost indistinguishable from other colorless or white minerals of the apatite supergroup, such as hedyphane, mimetite, pyromorphite, or fluorapatite, which can occur in similar forms. It differs from them in chemical composition (dominance of barium and calcium). It is distinguished from most apatites by its significantly higher density. ## Crystal Forms It forms short, prismatic crystals with a hexagonal cross-section, terminated by flat pinacoids. It also occurs as granular aggregates, radial aggregates, or as single, embedded grains.
Geological environment
## Genesis Morelandite is a mineral of metamorphic origin. It forms in metamorphosed, stratiform zinc, iron, and manganese ore deposits. In the type locality (Sterling Hill), it occurs within highly metamorphosed ore lenses in marbles (the so-called Franklin Marble). ## Mineral Associations This mineral co-occurs with other, often rare minerals. In Sterling Hill, these include: franklinite, willemite, calcite, andradite, hardystonite, and baryte. In Långban, Sweden, it is accompanied by: berzeliite, braunite, hausmannite, and calcite. ## Localities The most important and historically significant localities for this very rare mineral are the Sterling Hill Mine in New Jersey (USA) and the deposits in Långban (Värmland, Sweden). These are the only places from which well-documented specimens originate.
Rarity
Very rare
For collectors
## Quality Criteria Specimens with well-formed, sharp, and transparent crystals are most highly valued, even if they are small. Contrast with the matrix is very important, for example, white morelandite crystals on dark franklinite. Due to its rarity, even microscopic but well-formed crystals in a rich mineral association are considered valuable. ## Popular Localities Specimens from the two classic localities, Sterling Hill in the USA and Långban in Sweden, are by far the most sought after by collectors. Material from these places is considered exemplary for the species.
Care and storage
## Cleaning Specimens should be cleaned with great care, using a soft brush to remove dust. If necessary, distilled water can be used. Ultrasonic cleaners should be avoided, as they can damage the brittle crystals. ## What to Avoid Morelandite is an arsenate, which means it contains toxic arsenic. Inhaling dust during cleaning or preparation of the specimen should be avoided. Hands should be thoroughly washed after any contact with the mineral. It must not be heated or exposed to acids, which can decompose it, releasing toxic compounds. Due to its hardness of 4.5, it is susceptible to scratching by harder minerals (e.g., quartz). ## Storage It is recommended to store specimens in separate, sealed collector boxes to protect them from mechanical damage and dust. The label should include a warning about the mineral's toxicity. Store in a place inaccessible to children and pets.