2009/06/01 by F. C. Hawthorne, Neil A. Ball, Jim Nizamoff +1 · 1 citation
Environmental Science · Chemistry · Materials Science · #Chemical Synthesis and Characterization #Radioactive element chemistry and processing #Crystal Structures and Properties
paper · doi:10.1180/minmag.2009.073.3.415
openalex publication_date 2009/06/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/11
Abstract Zigrasite, ideally MgZr(PO 4 ) 2 (H 2 O) 4 , is a new secondary phosphate mineral from the giant 1972 gem tourmaline-bearing pocket at the Dunton Quarry, Newry, Oxford County, Maine, USA. It occurs as subhedral blocky grains sometimes exceeding 1 mm in maximum dimension and perched on tourmaline. These grains are complex aggregates ofthree distinct phases, zigrasite and two unnamed phases: the Ca analogue of zigrasite, CaZr(PO 4 ) 2 (H 2 O) 4 , and Zr(PO 3 OH) 2 (H 2 O) 4 . Zigrasite is associated with tourmaline, microcline, quartz, albite, beryl, amblygonite-montebrasite, childreniteeosphorite and apatite, and crystallized as one of the latest minerals during pocket formation. It is offwhite to pale yellow or light tan, translucent with a white streak and a vitreous lustre, and shows light blue to pale yellow cathodoluminescence. Mohs hardness is 3 and the measured and calculated densities are 2.76(4) and 2.66 g/cm 3 . The mineral has imperfect cleavage in two directions, parallel to (010) and (001), shows no parting, is brittle and has a hackly fracture. In transmitted light, it is colourless and non-pleochroic, biaxial negative with α 1.597(1), β 1.622 (1), γ 1.635 (1), with 2V (meas) = 65.5(4)º and 2V (calc.) = 71º. Zigrasite is triclinic, P , a 5.3049(2) Å, b 9.3372(4) Å, c 9.6282(5) Å, α 97.348(1)º, β 91.534(1)º, γ 90.512(4)º, V 472.79(5) Å3, Z = 2. The seven strongest lines in the X-ray powder diffraction pattern are as follows: d (Ê), I , ( hkl ): 9.550, 100, (001); 4.108, 70, ; 4.008, 50, (111); 4.589, 40, (110); 3.177, 40, (112); 3.569, 30, (0 2), 2.660, 30, (200),(11),(130); 3.273, 20, ( 12). Chemical analysis by electron microprobe gave P 2 O 5 37.59, ZrO 2 32.27, HfO 2 0.34, FeO 0.20, MgO 10.37, ZnO 0.17, F 0.13, LOI 18.60, less O:F 0.05 = total 99.62 wt.%. The resulting empirical formula is ( –)Σ= 0.99 (Zr 0.99 Hf 0.01 )Σ= 1.00 P 2.00 O 8 (H 2 O) 4 on the basis of12 O atoms with H 2 O = 4 per formula unit from crystal-structure analysis, and the end-member formula is MgZr(PO 4 ) 2 (H 2 O) 4 .