Rubicline
{{Short description|Rubidium feldspar mineral}}
{{Infobox mineral
| name = Rubicline
| category = Tectosilicate minerals, feldspar group
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| image = Rubicline.jpg
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| formula = (Rb, K)[AlSi3O8]
| molweight = 313.11 g/mol
| strunz = 9.FA.30
| dana =
| system = Triclinic
| class = Pinacoidal ({{overline|1}})
(same H-M symbol)
| symmetry = P{{overline|1}}
| color = Colorless
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| cleavage = {001}
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| luster = Vitreous
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| diaphaneity = Transparent
| gravity =
| density = 2.8 g/cm3
| polish =
| opticalprop = biaxial
| refractive = nα = 1.520 nβ = 1.524 nγ = 1.527
| birefringence = δ = 0.007
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| dispersion = Strong
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| other = Radioactive
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| references = [http://www.webmineral.com/data/Rubicline.shtml Rubicline at Webminerals][http://www.mindat.org/min-7276.html Rubicline at Mindat]
}}
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).{{cite journal|title = Rubicline, a new feldspar from San Piero in Campo, Elba, Italy|author = Teertstra, David K.|journal = American Mineralogist|date = December 2008|volume = 83|issue = 11–12|pages = 1335–1339|url = http://ammin.geoscienceworld.org/cgi/content/abstract/83/11-12_Part_1/1335|display-authors=etal|doi = 10.2138/am-1998-11-1223}}
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{{cite journal|title = Subsolidus rubidium-dominant feldspar from the Morrua pegmatite, Mozambique: paragenesis and composition|author1=Teertstra, D. K. |author2=Cerny, P. |author3=Hawthorne, F. C. |journal = Mineralogical Magazine|date = 1999|volume = 63|issue = 3|pages = 313–320|issn = 0026-461X|doi=10.1180/002646199548538|bibcode=1999MinM...63..313T |citeseerx=10.1.1.607.9008 |s2cid=53607085 }} and the Kola Peninsula in Russia.{{cite web|title = Rubicline R070044|url = http://rruff.info/rubicline/names/asc/|publisher = RRUFF|accessdate = 15 February 2010}} 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.{{cite journal|title = Refinement of the crystal structure of a synthetic non-stoichiometric Rb-feldspar|author1=Kyono, A. |author2=Kimata, M. |name-list-style=amp |journal = Mineralogical Magazine|date = August 2001|volume = 65|issue = 4|pages = 523–531|url = http://rruff.info/uploads/MM65_523.pdf|doi=10.1180/002646101750377542|bibcode=2001MinM...65..523K |citeseerx=10.1.1.580.3483 |s2cid=95219083 }} 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.{{cite web|title = Rubicline|url = http://www.mindat.org/min-7276.html|publisher = Mindat.org|author1=Ralph, Jolyon |author2=Chau, Ida |name-list-style=amp |date = 2010|accessdate = 15 February 2010}} 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 rubidium compounds, rubicline is mildly radioactive. Activity and dose rate of various amounts of rubicline are listed in the table below.
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!Specimen weight/size !Calculated !Calculated !Estimated !Estimated | ||||
| 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