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Thomasclarkite-(Y) mineral

Hydrated sodium-yttrium bicarbonate-hydroxide mineral with current September 2026 IMA-CNMNC approved formula NaY(HCO3)(OH)3(H2O)2·2H2O and approval number IMA 1997-047. Grice and Gault (1998) characterized the cotype specimens (CMNMI 81553, CMNMI 81554, and CMNMI 81555, formerly provisional phase UK93) from a large late-stage hydrothermal miarolitic cavity on level 7 of the Poudrette quarry, Mont Saint-Hilaire, Rouville County, Quebec, Canada. Electron-microprobe WDS analysis (2 points on 1 grain, p. 1295) combined with thermogravimetric analysis yielded Na2O 6.72, CaO 0.33, Y2O3 14.52, La2O3 8.63, Ce2O3 17.11, Pr2O3 1.92, Nd2O3 5.63, Sm2O3 1.22, Gd2O3 1.22, Dy2O3 2.04, Er2O3 2.20, Yb2O3 1.32, ThO2 0.54, F 0.17, CO2 12.00, H2O 26.60, O=F -0.07, total 102.10 wt%, corresponding on the basis of 10 anions to the empirical formula (Na0.80Ce0.18Ca0.02)Sigma1.00(Y0.48La0.20Ce0.21Pr0.04Nd0.12Sm0.03Gd0.03Dy0.04Er0.04Yb0.03)Sigma1.22(HCO3)[O6.97F0.03]H9.93. Single-crystal X-ray diffraction refined in monoclinic space group P2 (pseudotetragonal cell a = 4.556(1), b = 13.018(6), c = 4.556(2) A, beta = 90.15(3) degrees, V = 270.2(2) A3, Z = 1, R = 0.055, wR2 = 0.157 for 1616 observed reflections with > 4sigma(F) using reflection twin law (101), twin fraction 0.496(9)) revealed a layered structure with 2-fold orientational disorder of the bicarbonate [HCO3]- groups and half-occupied W7 and OH4 sites. Hydrogen positions were not directly located by X-ray diffraction; the bicarbonate versus carbonate assignment rests on charge balance, C-O bond- valence sums, and infrared absorption bands. Laboratory thermogravimetric analysis showed a two-stage weight loss up to 510 degrees C, and the mineral dissolves readily with strong effervescence in 10% HCl. Distinct from adamsite-(Y), shomiokite-(Y), and elemental yttrium; no criticality designation, microbial mechanism, or industrial recovery yield is asserted.

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Identifiers & Classification

System Identifier Label
IMA IMA:1997-047 Thomasclarkite-(Y)

Microbial & Biochemical Mechanisms (1)

Thomasclarkite-(Y) other Laboratory thermal dehydration and dec

Laboratory thermal dehydration and decarbonation of natural thomasclarkite-(Y)

other

Heating a 5.970 mg powdered sample of natural thomasclarkite-(Y) under flowing dry nitrogen from room temperature to 1000 degrees C produced two resolved weight-loss stages between 20 and 510 degrees C totaling 2.302 mg (38.6 wt%), attributed by the authors to loss of weakly H-bonded [H2O] groups between 20 and 110 degrees C (1.222 mg, 20.5 wt%) followed by a bimodal DTG loss between 380 and 510 degrees C (1.080 mg, 18.1 wt%) from decomposition of (OH)- and (HCO3)- groups into H2O and CO2.

Experimental Context & Analytical Limits:
Thermal analysis in Grice and Gault (1998), pp. 1295-1296 and Figure 3 used a 5.970 mg powdered natural sample from Mont Saint-Hilaire in a Mettler-Toledo TA8000 / TG50 thermal system with an M3 microbalance heated from room temperature to 1000 degrees C at 5 degrees C/min under dry nitrogen flowing at 200 mL/min. Because the 380-510 degrees C step co- evolved H2O and CO2 without online gas analysis, the authors calculated ideal CO2 (12.0 wt%) from crystal-structure stoichiometry and subtracted it from the total 38.6 wt% TG weight loss to obtain 26.6 wt% total H2O.
Curated Evidence Points:
Pages 1295-1296 and Figure 3 report two TG/DTG weight-loss stages on the 5.970 mg sample (total loss 2.302 mg or 38.6 wt%): Stage 1 (20-110 degrees C) lost 1.222 mg (20.5 wt%, assigned to loss of weakly H-bonded [H2O] molecules), and Stage 2 (380-510 degrees C, bimodal DTG peak) lost 1.080 mg (18.1 wt%, assigned to combined loss of H2O and CO2 from (OH)- and (HCO3)- decomposition).
Because the bimodal 380-510 degrees C DTG peak reflects overlapping dehydroxylation and decarbonation without evolved-gas spectroscopy or diffraction identification of the heated solid residue, the partition of the 38.6 wt% total loss into 26.6 wt% H2O and 12.0 wt% CO2 relies on the ideal structural content of one (HCO3)- group per formula unit.

Sources & References

  1. ima_2026_09: IMA-CNMNC, The New IMA List of Minerals, September 2026, PDF page 216, Thomasclarkite-(Y) row: formula NaY(HCO3)(OH)3(H2O)2·2H2O, status A, IMA No. 1997-047, country Canada, reference Canadian Mineralogist 36 (1998), 1293; column definitions on PDF page 1.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-18)
  2. grice_gault_1998_thomasclarkite: Grice JD, Gault RA (1998), Thomasclarkite-(Y), a new sodium - rare-earth- element bicarbonate mineral species from Mont Saint-Hilaire, Quebec, Canadian Mineralogist 36:1293-1300. Complete 8-page primary PDF visually inspected: occurrence, cotypes CMNMI 81553-81555, and physical properties pp. 1293-1295; WDS chemical analysis and TG/DTG thermal analysis Figure 3 pp. 1295-1296; XRPD Table 1 p. 1296; monoclinic P2 crystal-structure refinement, (101) twinning, bicarbonate 2-fold disorder, and bond-valence Tables 2-5 pp. 1296-1299.
    https://www.rruff.net/doclib/cm/vol36/CM36_1293.pdf (accessed 2026-10-18)

Curation History

Timestamp Curator Action Summary
2026-10-19T05:22:00Z antigravity CREATE Created thomasclarkite-(Y) mineral record with verified IMA identity, monoclinic P2 disordered-bicarbonate structure characterization, and bounded laboratory TG/DTG thermal decomposition mechanism from the 1998 primary study.

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