Rubicline, also referred to as Rb-microcline, is the rubidium

Rubidium

Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group. Its atomic mass is 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other elements in group 1, such as very rapid...

 analogue of microcline

Microcline

Microcline is an important igneous rock-forming tectosilicate mineral. It is a potassium-rich alkali feldspar. Microcline typically contains minor amounts of sodium. It is common in granite and pegmatites. Microcline forms during slow cooling of orthoclase; it is more stable at lower temperatures...

, an important tectosilicate mineral. Its chemical formula

Chemical formula

A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 is (Rb, K)[AlSi₃O₈] with an ideal composition of RbAlSi₃O₈. Chemical analysis by electron microprobe

Electron microprobe

An electron microprobe , also known as an electron probe microanalyzer or electron micro probe analyzer , is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials...

 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

Caesium oxide

Caesium oxide or cesium oxide describes inorganic compounds composed of caesium and oxygen. The following binary oxides of caesium are known: Cs11O3, Cs4O, Cs7O, and Cs2O. Both the oxide and suboxides are brightly coloured...

 (Cs₂O) and iron(III) oxide

Iron(III) oxide

Iron oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron oxide , which is rare, and iron oxide , which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main...

 (Fe₂O₃).

Rubicline was first discovered in 1998 in Elba

Elba

Elba is a Mediterranean island in Tuscany, Italy, from the coastal town of Piombino. The largest island of the Tuscan Archipelago, Elba is also part of the National Park of the Tuscan Archipelago and the third largest island in Italy after Sicily and Sardinia...

, Italy

Italy

Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

, by a team from the University of Manitoba

University of Manitoba

The University of Manitoba , in Winnipeg, Manitoba, Canada, is the largest university in the province of Manitoba. It is Manitoba's most comprehensive and only research-intensive post-secondary educational institution. It was founded in 1877, making it Western Canada’s first university. It placed...

. It was the first mineral to have been discovered with rubidium as an essential constituent. It has also been found in Mozambique

Mozambique

Mozambique, officially the Republic of Mozambique , is a country in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi and Zambia to the northwest, Zimbabwe to the west and Swaziland and South Africa to the southwest...

 and the Kola Peninsula

Kola Peninsula

The Kola Peninsula is a peninsula in the far northwest of Russia. Constituting the bulk of the territory of Murmansk Oblast, it lies almost completely to the north of the Arctic Circle and is washed by the Barents Sea in the north and the White Sea in the east and southeast...

 in Russia

Russia

Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

. 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

Albite

Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi3O8. It is a tectosilicate. Its color is usually pure white, hence...

 in a solvent of RbCl. This mixture was then placed in a silver tube containing H₂O, heated to 400 °C

Celsius

Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...

 and pressurized to 60 MPa

Pascal (unit)

The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...

.

Unlike microcline, which can be yellow, red, or green, rubicline is colorless. It is also transparent

Transparency and translucency

In the field of optics, transparency is the physical property of allowing light to pass through a material; translucency only allows light to pass through diffusely. The opposite property is opacity...

, brittle

Brittle

A material is brittle if, when subjected to stress, it breaks without significant deformation . Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound. Brittle materials include most ceramics and glasses ...

, and has a vitreous lustre. Rubicline has been classified as both triclinic and monoclinic. The crystal does not show twinning

Crystal twinning

Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals....

. Rubicline is a feldspar in the Strunz classification

Strunz classification

Nickel–Strunz classification is a scheme for categorizing minerals based upon their chemical composition, introduced by German mineralogist Karl Hugo Strunz in his 1941 Mineralogische Tabellen. The 4th edition was edited by Christel Tennyson too . It was followed by A.S...

 group 9.FA.30. Other minerals in this group include adularia, anorthoclase

Anorthoclase

The mineral anorthoclase is a crystalline solid solution in the alkali feldspar series, in which the sodium-aluminium silicate member exists in larger proportion. It typically consists of between 10 and 36 percent of KAlSi3O8 and between 64 and 90 percent of NaAlSi3O8....

, buddingtonite

Buddingtonite

Buddingtonite is an ammonium feldspar with formula: NH4AlSi3O8 . It forms in hydrothermal areas by alteration of primary feldspar minerals. It is an indicator of possible gold and silver deposits, as they can become concentrated by hydrothermal processes...

, celsian

Celsian

Celsian is an uncommon feldspar mineral, barium aluminosilicate, BaAl2Si2O8. The mineral occurs in contact metamorphic rocks with significant barium content. Its crystal system is monoclinic, and it is white, yellow, or transparent in appearance. In pure form, it is transparent...

, hyalophane

Hyalophane

Hyalophane or jaloallofane is a crystalline mineral with chemical formula [AlSi2O8] and a hardness of 6 – 6½. It is part of the feldspar group of tectosilicates, and is considered a barium-rich potassium feldspar...

, microcline, monalbite, orthoclase

Orthoclase

Orthoclase is an important tectosilicate mineral which forms igneous rock. The name is from the Greek for "straight fracture," because its two cleavage planes are at right angles to each other. Alternate names are alkali feldspar and potassium feldspar...

, and sanidine

Sanidine

Sanidine is the high temperature form of potassium feldspar 4O8. Sanidine most typically occurs in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the monoclinic crystal system. Orthoclase is a monoclinic polymorph stable at lower temperatures...

.

Rubicline is radioactive as summarized in the table below.

Specimen weight/size	Calculated activity (Bq Becquerel The becquerel is the SI-derived unit of radioactivity. One Bq is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. The Bq unit is therefore equivalent to an inverse second, s−1... )	Calculated activity (Ci Curie The curie is a unit of radioactivity, defined asThis is roughly the activity of 1 gram of the radium isotope 226Ra, a substance studied by the pioneers of radiology, Marie and Pierre Curie, for whom the unit was named. In addition to the curie, activity can be measured using an SI derived unit,... )	Estimated activity GR(api)	Estimated exposure (mRem Röntgen equivalent man Named after Wilhelm Röntgen , the roentgen equivalent in man or rem is a unit of radiation dose equivalent... )/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