• journal_title：American Mineralogist
• Contributor：Peter Bačík ; Jan CemPírek ; Pavel Uher ; Milan Novák ; Daniel Ozdín ; Jan FiliP ; Radek Škoda ; Karel Breiter ; Mariana Klementová ; Rudolf ĎuĎa ; Lee a. Groat
• Publisher：Mineralogical Society of America
• Date：2013-02-01
• Format：text/html
• Language：en
• Identifier：10.2138/am.2013.4293
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：98
• issue：2-3
• firstpage：485
• section：Article

Oxy-schorl (IMA 2011-011), ideally Na(Fe²⁺b>2b>Al)Alb>6b>Sib>6b>O1b>8b>(BOb>3b>)b>3b>(OH)b>3b>O, a new mineral species of the tourmaline supergroup, is described. In Zlatá Idka, Slovak Republic (type locality), fan-shaped aggregates of greenish black acicular crystals ranging up to 2 cm in size, forming aggregates up to 3.5 cm thick were found in extensively metasomatically altered metarhyolite pyroclastics with Qtz+Ab+Ms. In Přibyslavice, Czech Republic (co-type locality), abundant brownish black subhedral, columnar crystals of oxy-schorl, up to 1 cm in size, arranged in thin layers, or irregular clusters up to 5 cm in diameter, occur in a foliated muscovite-tourmaline orthogneiss associated with Kfs+Ab+Qtz+Ms+Bt+Grt. Oxy-schorl from both localities has a Mohs hardness of 7 with no observable cleavage and parting. The measured and calculated densities are 3.17(2) and 3.208 g/cm³ (Zlatá Idka) and 3.19(1) and 3.198 g/cm³ (Přibyslavice), respectively. In plane-polarized light, oxy-schorl is pleochroic; <em>Oem> = green to bluish-green, <em>Eem> = pale yellowish to nearly colorless (Zlatá Idka) and <em>Oem> = dark grayish-green, <em>Eem> = pale brown (Přibyslavice), uniaxial negative, ω = 1.663(2), ɛ = 1.641(2) (Zlatá Idka) and ω = 1.662(2), ɛ = 1.637(2) (Přibyslavice). Oxy-schorl is trigonal, space group <em>Rem>3<em>mem>, <em>Zem> = 3, <em>aem> = 15.916(3) Å, <em>cem> = 7.107(1) Å, <em>Vem> = 1559.1(4) ų (Zlatá Idka) and <em>aem> = 15.985(1) Å, <em>cem> = 7.154(1) Å, <em>Vem> = 1583.1(2) ų (Přibyslavice). The composition (average of 5 electron microprobe analyses from Zlatá Idka and 5 from Přibyslavice) is (in wt%): SiOb>2b> 33.85 (34.57), TiOb>2b> <0.05 (0.72), Alb>2b>Ob>3b> 39.08 (33.55), Feb>2b>Ob>3b> not determined (0.61), FeO 11.59 (13.07), MnO <0.06 (0.10), MgO 0.04 (0.74), CaO 0.30 (0.09), Nab>2b>O 1.67 (1.76), Kb>2b>O <0.02 (0.03), F 0.26 (0.56), Cl 0.01 (<0.01), Bb>2b>Ob>3b> (calc.) 10.39 (10.11), Hb>2b>O (from the crystal-structure refinement) 2.92 (2.72), sum 99.29 (98.41) for Zlatá Idka and Přibyslavice (in parentheses). A combination of EMPA, Mössbauer spectroscopy, and crystal-structure refinement yields empirical formulas (Nab>0.591b>Cab>0.103b>□b>0.306b>)b>∑1.000b>(Alb>1.885b>Fe²⁺b>1.108b>Mnb>0.005b>Tib>0.002b>)b>∑3.000b>(Alb>5.428b>Mgb>0.572b>)b>∑6.000b>(Sib>5.506b>Alb>0.494b>)b>∑6.000b>Ob>18b> (BOb>3b>)b>3b>(OH)b>3b>(Ob>0.625b>OHb>0236b>Fb>0.136b>Clb>0.003b>)b>∑1000b> for Zlatá Idka, and (Nab>0.586b>Cab>0.017b>Kb>0.006□0.391b>)b>∑1.000b>(Fe²⁺b>1.879b>Mnb>0.015b> Alb>1.013b>Tib>0.093b>)b>∑3.00b>(Alb>5.732b>Mgb>0.190b>Fe³⁺b>0.078b>)b>∑6.000b>(Sib>5.944b>Alb>0.056b>)b>∑6.000b>Ob>18b>(BOb>3b>)b>3b>(OH)b>3b>(Ob>0.579b>Fb>0.307b>OHb>0.115b>)b>∑1.000b> for Přibyslavice. Oxy-schorl is derived from schorl end-member by the AlOFeb>–1b>(OH)b>–1b> substitution. The studied crystals of oxy-schorl represent two distinct ordering mechanisms: disorder of R²⁺ and R³⁺ cations in octahedral sites and all O ordered in the <em>Wem> site (Zlatá Idka), and R²⁺ and R³⁺ cations ordered in the <em>Yem> and <em>Zem> sites and O disordered in the <em>Vem> and <em>Wem> sites (Přibyslavice).