{{Infobox mineral | name = Tuzlaite | category = Borates | image = | caption = | formula = NaCaB<sub>5</sub>O<sub>8</sub>(OH)<sub>2</sub> · 3H<sub>2</sub>O | IMAsymbol =Tuz | molweight = | strunz =6.EC.25 | system = Monoclinic | class =2/m - Prismatic | symmetry = P21/c | unit cell = a = 6.506(1) b = 13.280(3) c = 11.462(3) β = 92.97(2)◦ Z=4 | color = Colorless to White | habit = Prismatic crystals, elongated along [001] | twinning = | cleavage = On {001}, perfect | fracture = | tenacity = | mohs = 2 - 3 | luster = Silky to pearly | polish = | refractive = | opticalprop = Biaxial Positive | birefringence = | dispersion = | pleochroism = | fluorescence=None | absorption = | streak =White | gravity = | density =2.23 g/cm | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = | other = | references =<ref>Vladimir Bermanec, Thomas Armbruster, Darko Tibljas, Darko Sturman, Goran Kniewald; Tuzlaite, NaCa[B5O8(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.</ref><ref>Warr, Laurence N. (2021-05-18). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine: 1–30. {{doi|10.1180/mgm.2021.43}}. ISSN 0026-461X.</ref><ref>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/.</ref> }} '''Tuzlaite''' is a borate mineral, associated with halides, named after the Tuzla salt mines in Bosnia and Hercegovina. A multitude of rare evaporate minerals have been discovered there, it being the only major evaporate deposit in the Balkans.<ref name=":0">Vladimir Bermanec, Thomas Armbruster, Darko Tibljas, Darko Sturman, Goran Kniewald; Tuzlaite, NaCa[B<sub>5</sub>O<sub>8</sub>(OH)<sub>2</sub>]·3H<sub>2</sub>O, a new mineral with a pentaborate sheet structure from the Tuzla salt mine, Bosnia and Hercegovina. ''American Mineralogist'' 1994;; 79 (5-6): 562–569.</ref> This mineral has been approved as tuzlaite by the International Commission on New Minerals and Mineral Names.<ref>{{Cite journal |last=Warr |first=Laurence N. |date=2021-05-18 |title=IMA–CNMNC approved mineral symbols |journal=Mineralogical Magazine |volume=85 |issue=3 |pages=291–320 |doi=10.1180/mgm.2021.43 |bibcode=2021MinM...85..291W |issn=0026-461X|doi-access=free }}</ref>
== Occurrence == Tuzlaite is found alongside several rare evaporates such as northupite, searlesite, and bradleyite. Between the layers of salt, there are approximately 50m thick layers of grey to black dolomitic marls that occasionally get cut by white veinlets composed of the mineral tuzlaite.<ref name=":1" /> These veinlets can be surrounded by a coronitic halite phase that can be dissolved off with H<sub>2</sub>O, 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.<ref name=":0" />
== Physical and Optical Properties == Tuzlaite ranges from white to colorless with a perfect cleavage parallel to {001}. The hardness of the mineral is within the range of 2 to 3 on the Mohs Hardness scale. 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. Tuzalite decomposes in hydrochloric acid leaving a transparent solution with no residue, but does not react with H<sub>2</sub>O.<ref name=":0" />
Tuzlaite has refractive indices ''n''<sub>x</sub> = 1.532(2), ''n''<sub>y</sub> = 1.544(2), and ''n''<sub>z</sub> = 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''<sub>z</sub> = 82(1)°; 2''V''<sub>z</sub> = 80.9° was calculated from refractive indices. Indicatrix dispersion wasn't observed.<ref name=":0" />
== Chemistry == {| class="wikitable" | |(1) |(2) |- |B<sub>2</sub>O<sub>3</sub> |52.19 |52.24 |- |Al<sub>2</sub>O<sub>3</sub> |0.26 | - |- |CaO |14.64 |16.83 |- |SrO |0.21 | - |- |Na<sub>2</sub>O |10.25 |9.30 |- |H<sub>2</sub>O |21.66 |21.63 |- |Total |99.21 |100.00 |} (1) Tuzla mine in Bosnia-Herzegovina; average of six analyses by flamephotometry, TGA, and crystal-structure analysis; corresponds to Na<sub>1.00</sub>(Ca<sub>0.87</sub>Na<sub>0.10</sub>Sr<sub>0.01</sub>)<sub>Σ=0.98</sub>B<sub>4.98</sub>Al<sub>0.02</sub> O<sub>7.92</sub>(OH)<sub>2</sub> • 3H<sub>2</sub>O.<ref name=":1">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/ .</ref>
(2) NaCaB<sub>5</sub>O<sub>8</sub>(OH)<sub>2</sub> • 3H<sub>2</sub>O.<ref name=":1" />
== 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 H<sub>2</sub>O molecules, where Ca is eightfold coordinated by six borate O atoms and two H<sub>2</sub>O molecules. Na is sevenfold coordinated by four borate O atoms and three H<sub>2</sub>O 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 H<sub>2</sub>O molecules, which are linked by H bonds to the borate sheet.<ref name=":0" />
== See More == List of Minerals
== References == {{Reflist}} <references group="" responsive="1"></references>
Category:Wikipedia Student Program Category:Borate minerals Category:Evaporite Category:Monoclinic minerals