Definition
Volborthite is a rare copper vanadate mineral with the chemical formula Cu₃V₂O₇(OH)₂·2H₂O. It belongs to the category of secondary minerals that form through the alteration of primary vanadium‑bearing ores.
Overview
Volborthite typically occurs as prismatic or tabular crystals, often displaying a deep blue to green‑blue coloration. It is most commonly found in oxidized zones of copper‑vanadium ore deposits, where it precipitates from hydrothermal fluids at relatively low temperatures. Known localities include the Czech Republic, Russia, the United States (Arizona), and several sites in Africa and Australia.
Etymology / Origin
The mineral is named after the Russian mineralogist and chemist George Volborth (also transliterated as Georgy Volbort), who made significant contributions to the study of vanadium minerals in the early 20th century.
Characteristics
- Crystal system: Monoclinic
- Space group: P2₁/c
- Unit cell parameters: a ≈ 10.36 Å, b ≈ 7.65 Å, c ≈ 7.03 Å; β ≈ 115.2° (values may vary slightly among studies)
- Hardness: 3–3.5 on the Mohs scale
- Specific gravity: 3.8–4.0
- Optical properties: Biaxial (+); refractive indices nα ≈ 1.788, nβ ≈ 1.802, nγ ≈ 1.814; measured 2V angle ≈ 70°
- Pleochroism: Distinct, ranging from pale blue to deep blue depending on crystal orientation
- Solubility: Soluble in dilute hydrochloric acid, releasing copper and vanadium ions
Volborthite is of interest to mineral collectors due to its vivid color and relatively well‑formed crystals, though it is not considered a major ore of copper or vanadium because of its rarity.
Related Topics
- Copper minerals: malachite, azurite, cuprite
- Vanadium minerals: vanadinite, descloizite, roscoelite
- Secondary oxidation minerals: commonly form in the supergene enrichment zones of base‑metal deposits
- Mineral classification systems: Strunz classification (8.BB.20) and Dana classification (40.03.02.01)
Note: The information presented reflects current scientific consensus as of the latest available mineralogical literature.