What is Kupletskite?
Kupletskite is a complex manganese-titanium silicate of the astrophyllite group, prized for bronze-brown crystals from alkaline complexes.
Mineralogy and crystal structure
Reference formula: K2(Mn,Fe)7Ti2Si8O24(O,OH)7. Kupletskite has a complex layered silicate structure with variable potassium, manganese, iron, titanium and niobium. Polytypism and substitutions are common, so the displayed COD model is a representative kupletskite polytype. Kupletskite is classified with silicates and has a triclinic crystal system. Typical hardness is 4–5 on the Mohs scale and specific gravity is approximately 3.3–3.5.
Colour, lustre and habit
Typical colours include brown, reddish-brown, black, yellow-brown. The usual prismatic, bladed, radiating habit and vitreous, pearly, sub-metallic lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Kupletskite forms in or is associated with alkaline nepheline-syenite complexes and late-stage pegmatitic cavities. Important documented localities include the Lovozero massif in Russia, Mont Saint-Hilaire in Canada and Greenland.
Bronze geometry for the advanced collector
Kupletskite brings the visual language of a rare-element pegmatite into a cabinet: dark bronze colour, sharp blades and a formula full of geological information. It is a strong specimen for collectors who enjoy complex silicates and classic alkaline localities.
Collecting and care
Protect bladed crystals from impact and avoid aggressive cleaning that can remove matrix or alter soft surfaces.
