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Monteregianite-(Y) mineral

Hydrated potassium-sodium-yttrium double-sheet silicate mineral with current September 2026 IMA-CNMNC approved formula KNa2YSi8O19·5H2O, status Rn (renamed), and special-procedure tag 1987 s.p. (originally approved as monteregianite by the IMA Commission on New Minerals and Mineral Names prior to publication by Chao 1978, and suffixed Monteregianite-(Y) in 1987; listed under 1987 s.p. in the IMA Master List rather than a numbered CURIE). Chao (1978, pp. 561–562) described the holotype specimen (preserved at the National Museum of Natural Sciences, Ottawa, specimen 37130; formerly known as UK-6 in Chao et al. 1967) from miarolitic cavities, thermally metamorphosed inclusions, and rheomorphic breccias in nepheline syenite at Mont St-Hilaire, Quebec, Canada, where it is usually associated with calcite, pectolite, microcline, albite, aegirine, and arfvedsonite and minor amounts of phlogopite, fluorite, quartz, ekanite, sepiolite, ashcroftine, lorenzenite, narsarsukite, natrolite, harmotome, apophyllite, molybdenite, and pyrite. Chemical analysis performed by D.C. Mah on approximately one gram of hand-picked colorless material following the procedures of Hounslow & Moore (1966), combined with electron-microprobe analysis for Y2O3 and thermogravimetric/thermal analysis to 1000 °C for H2O (Chao 1978, Table 3 and prose, pp. 561, 563), gave SiO2 60.30, Al2O3 0.50, Y2O3 11.97, CaO 0.65, MgO 0.15, BaO 0.35, MnO n.d., FeO n.d., Na2O 9.14, K2O 5.36, H2O 11.40, total 99.82 wt%, corresponding to the empirical formula (Na4.50K1.80)(Y1.85Ca0.20Mg0.06Ba0.04)(Si15.87Al0.15)O38·10.02H2O (printed in the Abstract on p. 561 with minor rounding/typographical variants Na4.56K1.80, Ca0.19, and Al0.16), simplified to (Na,K)6Y2Si16O38·10H2O; a partial electron-microprobe analysis of a mauve variety reported in prose on p. 563 gave 10.67% Y2O3, 1.38% MnO, 5.89% K2O, and 9.37% Na2O. Physical, optical, and crystallographic determinations in Chao (1978, pp. 561–563, Table 1 on p. 562, and Table 2 on p. 563 comparing monteregianite with the macdonaldite-group minerals rhodesite, macdonaldite, and delhayelite) show needle-shaped crystals in irregular and radiating clusters (Fig. 1), elongate tabular crystals in parallel groups (Fig. 2), or irregular micaceous masses (0.05 to 3 mm, bounded by {010}, {001}, and {100} pinacoids and occasional {101} prisms), colorless, white, grey, or rarely mauve or pale green color, white streak, vitreous to silky lustre, perfect {010}, very good {001}, and good to fair {100} cleavages, Mohs hardness ~3½, Dmeas = 2.42(2) g/cm3 (determined by flotation in diluted bromoform and by use of a Berman balance), Dcalc = 2.391 g/cm3 (for Z = 4 of (Na,K)6Y2Si16O38·10H2O), ready etching by cold 1:1 HCl, HNO3, and H2SO4 along cleavage planes (pp. 561–562), and biaxial (+) optics (Na light, spindle stage) with alpha = 1.510(1), beta = 1.513(1), gamma = 1.517(1), 2Vmeas = 87(1)°, 2Vcalc = 82°, orientation X = c, Y = a, Z = b, optic plane perpendicular to the axis of elongation (a), and inconspicuous dispersion; Weissenberg, precession, and least-squares powder-diffraction refinement (Table 1, p. 562; 114.6 mm camera, CuKalpha radiation, lambda = 1.5418 Å, Si internal standard; strongest eight lines: 12.00 (100)(020), 7.03 (100)(200), 6.55 (40)(002), 6.02 (50)(220,040), 4.42 (100)(042), 3.405 (50)(062), 3.026 (50)(034,440), and 2.873 (80)(044) Å) initially indexed the mineral as orthorhombic Bmab or B2ab with a = 14.014(4), b = 23.910(5), c = 13.096(2) Å and a pronounced pseudocell with a and c halved in Pmmb, P2mb, or Pm2b. Ghose, Sen Gupta, and Campana (1987; spelled montregianite throughout their paper) determined and refined the crystal structure by single-crystal MoKalpha X-ray diffraction on a 0.34 x 0.32 x 0.34 mm Mont St. Hilaire cleavage fragment donated by G.Y. Chao (after an initial orthorhombic Cmca refinement on 2209 reflections to R = 0.066 showed anomalously large Si–O bond-length standard deviations, 13724 reflections were recollected on a Syntex P1 four-circle diffractometer to 2theta = 65°, yielding 5669 inequivalent and 4877 observed reflections refined to R = 0.059, Rw = 0.061; Tables 1–4, pp. 366–373), establishing true monoclinic (pseudo-orthorhombic, 2/m) symmetry in standard space group P21/n with a = 9.512(2), b = 23.956(4), c = 9.617(2) Å, beta = 93.85(1)°, V = 2186.5(6) Å3, Z = 2 for Na4K2Y2Si16O38·10H2O (Z = 4 for KNa2YSi8O19·5H2O), Dcalc = 2.41 g/cm3, and mu(MoKalpha) = 35.45 cm-1 (non-standard pseudo-orthorhombic setting C1121/a: a = 13.973(2), b = 13.064(2), c = 23.956(4) Å, gamma = 90.62(1)°, V = 4372.8(10) Å3, Z = 4, Table 1, p. 366). The structure consists of two types of layers alternating along [010] parallel to the (010) perfect cleavage (pp. 365, 370–373): (1) an open mixed octahedral sheet of isolated [YO6] octahedra (mean Y–O = 2.261(30) Å; octahedral Y site refined with 0.60 Y + 0.40 Ce in Table 2, p. 366, and prose, p. 370) and three distinct [NaO4(H2O)2] octahedra (Na(1) occupancy 0.95, mean Na–O = 2.493(32) Å for 6 bonds or 2.551 Å including a weak 7th O(5B) bond at 2.900(6) Å; Na(2A) occupancy 0.47, mean 2.416(30) Å; Na(2B) occupancy 0.45, mean 2.411(26) Å; Table 2, p. 366, Table 4, p. 368, and prose, p. 371) forming elliptical eight-membered octahedral rings, and (2) an apophyllite-type double silicate sheet with four- and eight-membered tetrahedral rings (bridging Si(1) and Si(4) tetrahedra with mean Si–O = 1.598 Å and Si(1)–O(1)–Si(4) = 176.5(3)°, and six other tetrahedra with three bridging and one nonbridging oxygen and mean Si–O = 1.613 Å; Table 4, pp. 368–369, and prose, pp. 371–373) housing split ten-coordinate [KO6(H2O)4] sites (K(1) occupancy 0.62, mean K–O = 2.978 Å; K(2) occupancy 0.38, mean K–O = 2.991 Å, separated by 0.34 Å; Table 2, p. 366, Table 4, p. 368, and prose, p. 372) and six independent water positions W(1)–W(6) (W(1) and W(2) fully occupied at 1.0 in the octahedral sheet; W(3) occupancy 0.95, W(4) 0.46, W(5) 0.35, and W(6) 0.37 in the channels; Table 2, p. 366, and prose, p. 372). The second reference listed in the IMA Master List (Journal of Physical Chemistry B 102 (1998), 4379) was not inspected in full text and no claims from that 1998 study are asserted here. Distinct from macdonaldite-group silicates (rhodesite, macdonaldite, delhayelite), apophyllite, ashcroftine-(Y), and elemental yttrium; no criticality designation, microbial mechanism, or industrial recovery yield is asserted.

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Microbial & Biochemical Mechanisms (1)

Monteregianite-(Y) other Laboratory reversible zeolitic dehydra

Laboratory reversible zeolitic dehydration-rehydration and high-temperature vitrification of natural monteregianite-(Y)

other

Simultaneous thermogravimetric (TGA) and derivative thermogravimetric (DTG) analyses together with DTA (solid) and DTG (dashed) curves recorded at a heating rate of 10 °C/min in air (Chao 1978, pp. 563–564, Fig. 3) show that dehydration of monteregianite-(Y) begins almost immediately on heating and is essentially complete near 400 °C in three distinct stages at 25–80 °C, 80–200 °C, and 200–400 °C with weight loss in the approximate ratio 1:2:2, and a total weight loss of 11.40 wt% after heating to 1000 °C. On cooling from 650 °C to room temperature, approximately 99% of the lost water is recovered within two hours, and the rehydrated material yields an X-ray powder diffraction pattern identical to that of unheated monteregianite-(Y), demonstrating the zeolitic nature of the water. Material quenched from 750 °C shows signs of melting, and material quenched from 1000 °C is amorphous to X-rays. Infrared spectra (Chao 1978, pp. 563–564, Fig. 4) corroborate three groups of structurally distinct water via resolved O–H stretching bands at 3460, 3510, and 3610 cm-1 alongside H–O–H bending at 1630 cm-1, which Ghose, Sen Gupta, and Campana (1987, p. 372, Table 2 on p. 366, and Table 4 on p. 368) assign respectively to H-bonded octahedral-sheet water molecules W(1) and W(2) (occupancy 1.0, leaving near the 240 °C dehydration peak), weakly bifurcated H-bonded channel water W(3) (occupancy 0.95), and non-H-bonded channel water molecules W(4) (occupancy 0.46), W(5) (occupancy 0.35), and W(6) (occupancy 0.37) leaving at the start of the 80–200 °C stage after disordered channel water leaves at 25–80 °C.

Experimental Context & Analytical Limits:
Laboratory simultaneous TGA/DTG, DTA (10 °C/min in air), quenching, room-temperature rehydration, X-ray powder diffraction, and infrared spectroscopic experiments on natural Mont St-Hilaire monteregianite-(Y) reported by Chao (1978, pp. 563–564, Figs. 3–4), structurally correlated with octahedral and channel water sites W(1)–W(6) by Ghose, Sen Gupta, and Campana (1987, pp. 365–366, 368, 372, Tables 2 and 4).
Curated Evidence Points:
Pages 563–564 and Figures 3–4 document simultaneous TGA and DTG analyses and DTA/DTG curves (heating rate 10 °C/min in air) showing three-stage dehydration at 25–80 °C, 80–200 °C, and 200–400 °C in an approximate 1:2:2 weight-loss ratio, 11.40 wt% total weight loss after heating to 1000 °C, ~99% recovery of lost water within two hours on cooling from 650 °C with an X-ray powder diffraction pattern identical to unheated monteregianite, signs of melting when quenched from 750 °C, X-ray amorphization when quenched from 1000 °C, and IR water bands at 1630 cm-1 (H–O–H bending) and 3460, 3510, and 3610 cm-1 (O–H stretching).
Pages 365–366, 368, and 372 and Tables 2 and 4 resolve six independent water positions in the monoclinic P21/n double-sheet silicate structure: two fully occupied octahedral-sheet water molecules W(1) and W(2) (occupancy 1.0, bonded to two Na atoms each and H-bonded to O(10A)/O(10B) at 2.874 and 3.019 Å, matched to the 3460 cm-1 IR band and the 240 °C dehydration peak) and four partially occupied channel water sites W(3) (occupancy 0.95, bonded to K at 2.89 Å and H-bonded to W(4)/W(5) at 2.984 and 2.987 Å, matched to the 3510 cm-1 band) and W(4)–W(6) (occupancies 0.46, 0.35, and 0.37, bonded to K without H bonding, matched to the 3610 cm-1 band and the onset of the 80–200 °C dehydration stage).

Sources & References

  1. ima_2026_09: IMA-CNMNC (Pasero M., 2026), The New IMA List of Minerals – A Work in Progress (Updated: September 2026), PDF p. 147, Monteregianite-(Y) row: status Rn, IMA No. 1987 s.p., formula KNa2YSi8O19·5H2O, country Canada, first reference Canadian Mineralogist 16 (1978), 561, second reference Journal of Physical Chemistry B 102 (1998), 4379.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-25)
  2. chao_1978_monteregianite: Chao GY (1978), Monteregianite, a new hydrous sodium potassium yttrium silicate mineral from Mont St-Hilaire, Quebec, The Canadian Mineralogist 16:561-565.
    https://www.rruff.net/doclib/cm/vol16/CM16_561.pdf (accessed 2026-10-25)
  3. ghose_1987_monteregianite: Ghose S, Sen Gupta PK, and Campana CF (1987), Symmetry and crystal structure of montregianite, Na4K2Y2Si16O38·10H2O, a double-sheet silicate with zeolitic properties, American Mineralogist 72:365-374.
    https://www.rruff.net/doclib/am/vol72/AM72_365.pdf (accessed 2026-10-25)

Curation History

Timestamp Curator Action Summary
2026-10-25T05:57:05Z antigravity CREATE Created Monteregianite-(Y) mineral record from the September 2026 IMA Master List (1987 s.p., status Rn), the complete 1978 Mont St-Hilaire type-description and thermal study by Chao (1978), and the complete 1987 monoclinic P21/n single-crystal structure refinement by Ghose, Sen Gupta, and Campana (1987).
2026-10-25T06:45:00Z antigravity EDIT Aligned all Chao (1978) and Ghose, Sen Gupta, and Campana (1987) table/page locators, analyst credit (D.C. Mah), printed empirical formula, powder XRD strongest lines, cleavage/density/optical/acid-etching properties, and TGA/DTG/DTA/IR thermal dehydration claims with the bounded primary-source passages to resolve #842 from independent review of PR #841.

Record source: data/records/monteregianite-y.yaml