Smaltite is a mineral belonging to the cobaltite group, composed primarily of a cobalt–nickel arsenide with the idealized chemical formula $(Co,Ni)As_2$. It crystallizes in the cubic crystal system and is typically found as metallic‑lustered, gray to silver‑white aggregates.
Classification
- Mineral class: Sulfides and sulfosalts (arsenides)
- Mineral group: Cobaltite group
- Crystal system: Isometric (cubic)
- Space group: P2₁3
Chemical composition
Smaltite is a solid‑solution series dominated by cobalt (Co) and nickel (Ni) substituting for one another within the arsenide lattice. Minor amounts of iron (Fe) and manganese (Mn) can also be present. The general formula is expressed as $(Co,Ni)As_2$, indicating variable Co:Ni ratios that differentiate smaltite from the closely related mineral cobaltite $(Co,Fe)AsS$.
Physical properties
| Property | Value |
|---|---|
| Color | Gray‑white to silvery metallic |
| Streak | Gray |
| Luster | Metallic |
| Hardness (Mohs) | 5.5–6 |
| Density | 6.5–7.0 g cm⁻³ (depends on Co/Ni ratio) |
| Cleavage | None; exhibits conchoidal fracture |
| Habit | Massive, granular, or as well‑formed cubic crystals |
Occurrence and geological context
Smaltite occurs in hydrothermal vein deposits, particularly in association with arsenopyrite, nickeline, cobaltite, and native cobalt. Notable localities include:
- Freiberg District, Saxony, Germany – classic European occurrences where the mineral was first described in the 19th century.
- Kola Peninsula, Russia – numerous cobalt‑nickel arsenide deposits.
- Southeastern United States (e.g., Tennessee, North Carolina) – minor occurrences within skarn and metamorphic assemblages.
- Canada (Ontario, Quebec) – reported in nickel‑cobalt sulfide and arsenide mineralization.
The mineral typically forms at moderate temperatures (200–400 °C) within reducing, arsenic‑rich fluids that interact with cobalt‑ and nickel‑bearing source rocks.
History of the term
The name “smaltite” derives from “smalt,” a deep blue cobalt glass pigment historically produced from cobalt ores. Early mineralogists adopted the term to denote cobalt‑rich arsenide minerals that were sources of the pigment. The designation was formalized in the mid‑19th century, although later mineralogical revisions have sometimes re‑classified smaltite specimens as members of the cobaltite–smaltite solid‑solution series.
Economic and industrial relevance
While smaltite itself is not a major ore mineral, its presence indicates cobalt and nickel enrichment in a deposit. Extraction of cobalt and nickel from smaltite‑bearing ores can be economically viable when associated with higher‑grade sulfide minerals. Historically, smaltite contributed to cobalt production for blue pigments and later for alloying and battery applications.
Associated minerals
- Cobaltite (CoAsS)
- Nickeline (NiAs)
- Arsenopyrite (FeAsS)
- Skutterudite ((Co,Ni)As₃)
Analytical identification
Identification of smaltite relies on a combination of:
- X‑ray diffraction (XRD) – characteristic cubic diffraction pattern matching space group P2₁3.
- Electron microprobe analysis – quantifies Co/Ni ratios and confirms arsenic dominance.
- Physical examination – metallic luster, conchoidal fracture, and specific gravity consistent with smaltite.
References (selected)
- Mindat.org. “Smaltite.” Accessed 2026.
- Palache, C., Berman, H., & Frondel, C. Dana’s System of Mineralogy, 8th ed., Wiley, 1991.
- IMA–CNMNC (International Mineralogical Association – Commission on New Minerals, Nomenclature and Classification). “Mineral Symbol: Sm” (2025).
Note: The information presented reflects current consensus in mineralogical literature and does not include unverified or speculative data.
