Apexite, NaMg(PO4)center dot 9H(2)O, a new struvite-type phase with a heteropolyhedral cluster

作者：Kampf Anthony R^*; Mills Stuart J; Nash Barbara P; Jensen Martin; Nikischer Tony

来源：American Mineralogist, 2015, 100(11-12): 2695-2701.

DOI：10.2138/am-2015-5457

• Apexite
• new mineral
• crystal structure
• struvite-type
• heteropolyhedral cluster
• hazenite
• Apex mine
• Nevada

Apexite (IMA2015-002), NaMg(PO4)center dot 9H(2)O, is a new mineral from the Apex mine, Lander County, Nevada, U.S.A., where it occurs as a low-temperature secondary mineral on massive quartz matrix in association with andersonite, calcite, cejkaite, gaylussite, and goethite. Apexite forms colorless needles up to 0.5 mm in length. The streak is white. Crystals are transparent and have vitreous to satiny luster. The Mohs hardness is about 2, the tenacity is brittle, the fracture is curved, and crystals exhibit one perfect cleavage on {100}. The measured density is 1.74(1) g/cm(3) and the calculated density is 1.741 g/cm(3). Electron microprobe analyses provided: Na2O 9.26, MgO 14.42, P2O5 23.31, H2O 53.01 (structure), total 100.00 wt% (normalized). The empirical formula (based on 13 O apfu) is: Na0.91Mg1.09P1.00O13.00H17.91. Apexite is triclinic, P (1) over bar, a = 6.9296(7), b = 11.9767(13), c = 14.9436(19) angstrom, alpha = 92.109(6), beta = 102.884(7), gamma = 105.171(7)degrees, V= 1160.9(2) angstrom(3), and Z = 4. The eight strongest lines in the X-ray powder diffraction pattern are [d(obs) in angstrom(I)(hkl)]: 14.63(35)(001); 5.11(61)(021,(1) over bar(1) over bar1,110,(1) over bar 20); 4.68(75)(0 (2) over bar2,(1) over bar(1) over bar2,1 (2) over bar1,0 (1) over bar3); 4.301(96)(102,013,022,(1) over bar 13); 4.008(44) ((1) over bar(1) over bar3,1 (2) over bar2); 2.876(46)(040); 2.762(100)((2) over bar(1) over bar3,2 (3) over bar1,0 (3) over bar4,(2) over bar 04,015); and 2.507(30)(212,025,(2) over bar(2) over bar3). Apexite is a new stmvite-type phase with a unique structure (R-1= 4.44% for 1401 F-o> 4 sigma F) consisting of four components: (1) a [Na2Mg4(H2O)(14)](10+) heteropolyhedral cation cluster; (2) a trans edge-sharing chain of Na(H2O)(6) octahedra; (3) an isolated PO4 group; and (4) an isolated H2O group. The structural components are linked to one another only via hydrogen bonds. Its structure is related to that of hazenite.

• 出版日期2015-12