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 lustre. Rubicline has been classified as both triclinic and monoclinic. The crystal does not show twinning. Rubicline is a feldspar in the Strunz classification group 9.FA.30. Other minerals in this group include adularia, anorthoclase, buddingtonite, celsian, hyalophane, microcline, monalbite, orthoclase, and sanidine.
Rubicline is radioactive as summarized in the table below.
* If held in hand for one hour.
1. ^ a b Rubicline at Webminerals