Tuzlaite is a

borate A borate is any of a range of boron oxyanions, anions containing boron and oxygen, such as orthoborate , metaborate , or tetraborate ; or any salt of such anions, such as sodium metaborate, and borax . The name also refers to esters of su ...

mineral, associated with

halide In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fl ...

s, named after the

Tuzla Tuzla (, , ) is the List of cities in Bosnia and Herzegovina, third-largest city of Bosnia and Herzegovina and the administrative center of Tuzla Canton of the Federation of Bosnia and Herzegovina. As of 2013, it has a population of 110,979 inha ...

salt mines in

Bosnia and Hercegovina Bosnia and Herzegovina, sometimes known as Bosnia-Herzegovina and informally as Bosnia, is a country in Southeast Europe. Situated on the Balkans, Balkan Peninsula, it borders Serbia to the east, Montenegro to the southeast, and Croatia to th ...

. A multitude of rare evaporate minerals have been discovered there, it being the only major evaporate deposit in the

Balkans The Balkans ( , ), corresponding partially with the Balkan Peninsula, is a geographical area in southeastern Europe with various geographical and historical definitions. The region takes its name from the Balkan Mountains that stretch throug ...

.Vladimir Bermanec, Thomas Armbruster, Darko Tibljas, Darko Sturman, Goran Kniewald; Tuzlaite, NaCa ₅O₈(OH)₂�3H₂O, a new mineral with a pentaborate sheet structure from the Tuzla salt mine, Bosnia and Hercegovina. ''American Mineralogist'' 1994;; 79 (5-6): 562–569. This mineral has been approved as tuzlaite by the International Commission on New Minerals and Mineral Names.

Occurrence

Tuzlaite is found alongside several rare evaporates such as

northupite Northupite is an uncommon evaporite mineral, with the chemical formula Na3Mg(CO3)2Cl. It occurs as colourless to dark grey or brown octahedral crystals and as globular masses. In synthetic material it forms a series with tychite (Na6Mg2(CO3)4SO4 ...

searlesite Searlesite is a sodium borosilicate mineral, with the chemical formula NaBSi2O5(OH)2. It was discovered in 1914 at Searles Lake, California, and was named to honor John W. Searles (16 November 1828 – 7 October 1897), California American pionee ...

, and bradleyite. Between the layers of salt, there are approximately 50m thick layers of grey to black

dolomitic Dolomite () is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite (see Dolomite (rock)). An alternative name sometimes ...

marl Marl is an earthy material rich in carbonate minerals, Clay minerals, clays, and silt. When Lithification, hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae. M ...

s that occasionally get cut by white veinlets composed of the mineral tuzlaite. These veinlets can be surrounded by a coronitic

halite Halite ( ), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, pi ...

phase that can be dissolved off with H₂O, leaving us with colorless to white crystals of tuzlaite up to 0.5mm in length. Most of these crystals can be intergrown, but some are suitable for X-ray single-crystal structure analysis.

Physical and Optical Properties

Tuzlaite ranges from white to colorless with a perfect cleavage parallel to . The hardness of the mineral is within the range of 2 to 3 on the

Mohs Hardness scale The Mohs scale ( ) of mineral hardness is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by the Germ ...

. The lustre of Tuzlaite is silky to pearly and is reliant on its growing conditions and the size of the crystal with no reaction to short-wave and long-wave

UV light Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of t ...

. Tuzalite decomposes in hydrochloric acid leaving a transparent solution with no residue, but does not react with H₂O. Tuzlaite has refractive indices ''n''_x = 1.532(2), ''n''_y = 1.544(2), and ''n''_z = 1.561(2). The optical orientation is ''Y'' = ''b'', ''Z'':''a'' = 14° (in acute angle β). It is optically positive with Δ = 0.029(l), measured with a compensator and calculated from refractive indices. The optic axial angle was measured as 2''V''_z = 82(1)°; 2''V''_z = 80.9° was calculated from refractive indices. Indicatrix dispersion wasn't observed.

Chemistry

(1) Tuzla mine in Bosnia-Herzegovina; average of six analyses by flamephotometry, TGA, and crystal-structure analysis; corresponds to Na_1.00(Ca_0.87Na_0.10Sr_0.01)_Σ=0.98B_4.98Al_0.02 O_7.92(OH)₂ • 3H₂O.John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, and Monte C. Nichols, Eds., Handbook of Mineralogy, Mineralogical Society of America, Chantilly, VA 20151-1110, USA. http://www.handbookofmineralogy.org/ . (2) NaCaB₅O₈(OH)₂ • 3H₂O.

Crystal Structure

All atoms in the structure for tuzlaite were refined and located. Tuzlaite has a pentaborate sheet structure with layers parallel to (001). These sheets are connected by Ca and Na coordinated with three H₂O molecules, where Ca is eightfold coordinated by six borate O atoms and two H₂O molecules. Na is sevenfold coordinated by four borate O atoms and three H₂O molecules. Na and Ca polyhedra form continuous chains with a Ca-Ca-Na-Na-Ca-Ca sequence. Face sharing occurs between Ca and Na polyhedra. Na and Ca polyhedral chains penetrate the ten-membered borate rings excentrically; thus the remaining space is filled by H₂O molecules, which are linked by H bonds to the borate sheet.

See More

List of Minerals This is a list of minerals which have Wikipedia articles. Minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various ''species''. Within a mineral speci ...

References

{{Reflist Wikipedia Student Program Borate minerals Evaporite Monoclinic minerals