Category Feldspar group Strunz classification 9.FA.30 Space group P1 | Formula
(repeating unit) (Rb, K)[AlSi3O8] Crystal system Triclinic | |
Crystal class Pinacoidal (1)
(same H-M symbol) | ||
Rubicline, also referred to as Rb-microcline, is the rubidium analogue of microcline, an important tectosilicate mineral. Its chemical formula is (Rb, K)[AlSi3O8] with an ideal composition of RbAlSi3O8. Chemical analysis by electron microprobe indicated the average weight of the crystal is 56.66% SiO2, 16.95% Al2O3, and 23.77% Rb2O, along with trace amounts of caesium oxide (Cs2O) and iron(III) oxide (Fe2O3).
Rubicline was first discovered in 1998 in Elba, Italy, by a team from the University of Manitoba. It was the first mineral to have been discovered with rubidium as an essential constituent. It has also been found in Mozambique and the Kola Peninsula in Russia. Rubicline occurs as small, abundant, rounded grains found within veins of rubidian microcline. Pure rubicline with an ideal potassium-free composition has never been found in nature. Rubicline was synthesized in 2001 by placing powdered albite in a solvent of RbCl. This mixture was then placed in a silver tube containing H2O, heated to 400 °C and pressurized to 60 MPa.
Unlike microcline, which can be yellow, red, or green, rubicline is colorless. It is also transparent, brittle, and has a vitreous luster. Rubicline has been classified as both triclinic and monoclinic. The crystal does not show twinning. Other minerals in this group include adularia, anorthoclase, buddingtonite, celsian, hyalophane, microcline, monalbite, orthoclase, and sanidine.
Like all potassium compounds, rubicline is mildly radioactive. Activity and dose rate of various amounts of rubicline are listed in the table below.