Calciosamarskite
Chemical formula: (Ca,Fe³⁺,Fe²⁺,Y)(Nb⁵⁺Ta⁵⁺,Ti⁴⁺)O₄
A rare mineral from the samarskite group, an oxide of niobium, tantalum, calcium, and iron, found in granitic pegmatites.
Properties
- Mohs hardness
- 5-6
- Color
- Black
- Luster
- Vitreous to resinous
- Streak
- Brown-grey
- Density
- 4.48
- Cleavage
- None
- Fracture
- Conchoidal
- Transparency
- Opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Calciosamarskite is identified by its high density, black color, resinous luster on fresh fracture, and occurrence in granitic pegmatites. Its conchoidal fracture is also characteristic. Identification is confirmed by analytical methods, such as X-ray diffraction (after heating the sample for recrystallization) and chemical composition analysis. ## Distinguishing from Similar Minerals It can be confused with other black, heavy pegmatite minerals, such as samarskite-(Y), euxenite-(Y), columbite, or uraninite. It differs from samarskite-(Y) by the dominance of calcium over yttrium. It is distinguished from euxenite by its chemical composition and subtle structural differences. Uraninite is significantly heavier and more strongly radioactive. Certain differentiation requires advanced laboratory tests. ## Crystal Forms Crystals are extremely rare, poorly formed, with a thick-tabular or prismatic habit. Most often, it forms irregular, massive aggregates embedded in the host rock (quartz, feldspar).
Geological environment
## Genesis Calciosamarskite is an accessory mineral in complex granitic pegmatites, especially those enriched in niobium, tantalum, and rare earth elements. It forms during the late stages of pegmatitic magma crystallization. ## Mineral Associations It most often co-occurs with quartz, microcline, albite, muscovite, biotite, as well as other rare minerals such as cyrtolite (a variety of zircon), euxenite-(Y), fergusonite-(Y), monazite, xenotime, uraninite, and allanite. ## Localities Important localities worldwide include Hybla and Madawaska in Ontario (Canada), from which the type material originates; pegmatites in the Iveland and Evje areas (Norway); the Urals (Russia); and some pegmatites in Colorado and North Carolina (USA).
Rarity
Very rare
For collectors
## Quality Criteria The most valued specimens by collectors are those with well-formed, even if only partially, crystals, which is a great rarity for this mineral. The size of the specimen and its association with other accompanying minerals, forming an aesthetic composition, are also important. Specimens embedded in quartz or feldspar are typical but less attractive than those showing crystal faces. ## Popular Localities Specimens from the historical localities in Ontario, Canada (Hybla, Madawaska) and from Norwegian pegmatites in the Iveland area are considered classic and most desirable.
Care and storage
## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush to remove dust. Avoid water and any chemical agents that could react with the mineral's surface. ## What to Avoid As a metamict mineral (with a crystal lattice destroyed by radiation), it is sensitive to temperature changes. It should not be heated. Avoid contact with chemicals, acids, and bases. Due to the presence of radioactive elements, direct, prolonged contact should be limited, and it should be stored away from other radiation-sensitive minerals. ## Storage It is recommended to store specimens in separate, padded boxes to prevent abrasions and mechanical damage. Keep it in a dry place, away from heat sources and direct sunlight. Due to its radioactivity, specimens should be stored in a well-ventilated area, away from places of constant human presence.