Roselite Crystals

Roselite is a captivating mineral species with a delicate rose-red to pink hue and a mesmerizing vitreous to resinous luster. Roselite (sometimes called alpha-roselite to distinguish it from its triclinic dimorph, beta-roselite) is a rare cobalt arsenate from the oxidation zone of cobalt arsenide deposits. 

Roselite owes its name to the mineralogist Gustave Rose of the University of Berlin. It occurs in small elongated prismatic crystals, pink to purple and purplish red, frequently grouped in spherolitic aggregates. It is a rare mineral coveted by collectors because of its attractive color.

Roselite's formation is attributed to the weathering of cobalt-rich mineral deposits, typically found in hydrothermal veins or pegmatites. As these primary minerals undergo decomposition in the presence of water and oxygen, they release cobalt ions, which combine with arsenic and other elements to form roselite. The process often occurs in acidic environments, contributing to the mineral's association with other arsenic-bearing minerals.

Crystals of Roselite. From: Aghbar Mine (Arhbar Mine), Aghbar, Bou Azer District, Tazenakht, Ouarzazate Province, Souss-Massa-Draâ Region, Morocco. Photo: Domenico Preite

Occurrence of Roselite

Roselite is a secondary mineral that can be found in cobalt-rich hydrothermal deposits at localities including Germany, Bou Azzer, Morocco, and Spain, among other localities. It is typically associated with other cobalt minerals, such as cobaltite and erythrite. It also forms in the oxidized zones of lead-zinc-silver deposits.

Physical Properties of Roselite:

• Formula: Ca₂(Co²⁺, Mg)[AsO₄]₂·H₂O 
• Crystal system: Monoclinic
• Color: Dark rose-red, pink
• Luster: Vitreous, Sub-Vitreous, Resinous
• Transparency: Transparent, Translucent
• Hardness: 3½ on Mohs scale
• Specific gravity: 3.46 - 3.74 g/cm3 (Measured) 3.65 g/cm3 (Calculated)
• Cleavage: Perfect on {010}, imperfect on {100}
• Fracture: Uneven
• Streak: White to pale pink