Article · Wikipedia archive · Last revised Aug 5, 2026

Rubicline

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).

Last revised
Aug 5, 2026
Read time
≈ 2 min
Length
511 w
Citations
16
Source
Wikipedia ↗
Rubicline
General
CategoryTectosilicate minerals
GroupFeldspar group
SeriesAlkali feldspar series
Formula(Rb, K)[AlSi3O8]
IMA symbolRub1
IMA statusApproved (1998)
Strunz classification9.FA.30
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
Space groupB2/m (no. 12)
Identification
Formula mass313.11 g/mol
ColorColorless
Cleavage{001}
Mohs scale hardness6
LusterVitreous
DiaphaneityTransparent
Density2.8 g/cm3
Optical propertiesbiaxial
Refractive indexnα = 1.520 nβ = 1.524 nγ = 1.527
Birefringenceδ = 0.007
DispersionStrong
Other characteristicsRadioactive
References23

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,4 along with trace amounts of caesium oxide (Cs2O) and iron(III) oxide (Fe2O3).5

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.5 It has also been found in Mozambique6 and the Kola Peninsula in Russia.7 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.4 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.4

Unlike microcline, which can be yellow, red, or green, rubicline is colorless. It is also transparent, brittle,5 and has a vitreous luster.8 Rubicline has been classified as both triclinic and monoclinic.48 The crystal does not show twinning. Other minerals in this group include adularia, anorthoclase, buddingtonite, celsian, hyalophane, microcline, monalbite, orthoclase, and sanidine.8

Like all rubidium compounds, rubicline is mildly radioactive. Activity and dose rate of various amounts of rubicline are listed in the table below.2

Specimen weight/size Calculated
activity (Bq) 		Calculated
activity (Ci) 		Estimated
activity GR(api) 		Estimated
exposure (mRem)/hr*
1000 g / 8.79 cm 183,355 4.96×10−6 8,449.31 2.78
100 g / 4.08 cm 18,336 4.96×10−7 844.93 0.28
10 g / 1.89 cm 1,834 4.96×10−8 84.49 0.03
1 g / 8.79 mm 183 4.96×10−9 8.45 0.00
0.1 g / 4.08 mm 18 4.96×10−10 0.84 0.00
0.01 g / 1.89 mm 2 4.96×10−11 0.08 0.00
0.001 g / 0.88 mm 0 4.96×10−12 0.01 0.00
  • If held in hand for one hour.
  • Government estimate of average annual exposure (360 mRem)
  • Max permissible adult dose 50,000 mRem/yr (hands), 15,000 mRem/yr (eyes)
  • Lethal exposure 400,000 to 500,000 mRem
References

References

  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. Rubicline at Webminerals
  3. Rubicline at Mindat
  4. Kyono, A. & Kimata, M. (August 2001). "Refinement of the crystal structure of a synthetic non-stoichiometric Rb-feldspar" (PDF). Mineralogical Magazine. 65 (4): 523–531. Bibcode:2001MinM...65..523K. CiteSeerX 10.1.1.580.3483. doi:10.1180/002646101750377542. S2CID 95219083.
  5. Teertstra, David K.; et al. (December 2008). "Rubicline, a new feldspar from San Piero in Campo, Elba, Italy". American Mineralogist. 83 (11–12): 1335–1339. doi:10.2138/am-1998-11-1223.
  6. Teertstra, D. K.; Cerny, P.; Hawthorne, F. C. (1999). "Subsolidus rubidium-dominant feldspar from the Morrua pegmatite, Mozambique: paragenesis and composition". Mineralogical Magazine. 63 (3): 313–320. Bibcode:1999MinM...63..313T. CiteSeerX 10.1.1.607.9008. doi:10.1180/002646199548538. ISSN 0026-461X. S2CID 53607085.
  7. "Rubicline R070044". RRUFF. Retrieved 15 February 2010.
  8. Ralph, Jolyon & Chau, Ida (2010). "Rubicline". Mindat.org. Retrieved 15 February 2010.