What is Rubicline?
Rubicline is a rare rubidium-rich feldspar, prized by specialists for its unusual alkali chemistry and relationship to highly evolved granitic pegmatites.
Mineralogy and crystal structure
Reference formula: (K,Rb)AlSi3O8. Rubicline is monoclinic in the selected COD model and belongs to the feldspar framework family. Rubidium and potassium substitution is central to its identity, so exact composition and locality matter. Rubicline is classified with silicates and has a monoclinic crystal system. Typical hardness is 6–6.5 on the Mohs scale and specific gravity is approximately 2.5–2.7.
Colour, lustre and habit
Typical colours include colourless, white, pink, yellow, grey. The usual tabular, prismatic, granular habit and vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Rubicline forms in or is associated with fractionated lithium-caesium-tantalum pegmatites and late-stage alkali-rich cavities. Important documented localities include Madagascar, Canada, Russia, Afghanistan and other evolved pegmatite localities.
A pale feldspar with rare rubidium chemistry
Rubicline is a collector mineral where the label is the value: a pale feldspar can record extreme fractionation and the late-stage chemistry of a lithium-rich pegmatite.
Collecting and care
Protect cleavage surfaces from impact and clean with mild water. Avoid acids and retain matrix and analytical information.
