Dondoellite, Ca2Fe(PO4)2·2H2O, a New Mineral Species Polymorphic with Messelite, from Rapid Creek, Yukon, Canada
Bibliographic record
Abstract
ABSTRACT A new mineral species, dondoellite, ideally Ca2Fe(PO4)2·2H2O, was found in the Grizzly Bear Creek, Dawson mining district, Yukon, Canada. It is polymorphic with messelite, a member of the fairfieldite group. Dondoellite occurs as spherical aggregates (diameters up to 2 cm) of radiating bladed crystals. Associated minerals include hydroxylapatite, siderite, and quartz. No twinning or parting is observed. The mineral is colorless to pale yellow in transmitted light, is transparent with white streak, and has vitreous luster. It is brittle and has a Mohs hardness of 3½–4, with perfect cleavage on {001}. The measured and calculated densities are 3.14(5) and 3.15 g/cm3, respectively. Optically, dondoellite is biaxial (+), with α = 1.649(5), β = 1.654(5), γ = 1.672(5) (white light), 2V (meas.) = 55(2)°, 2V (calc.) = 58°. An electron probe microanalysis yields an empirical formula (based on 10 O apfu) Ca1.99(Fe0.89Mg0.13Mn0.01)Σ1.03(P1.00O4)2·2H2O, which can be simplified to Ca2(Fe2+,Mg,Mn2+)(PO4)2·2H2O. Dondoellite is triclinic, space group P, a = 5.4830(2), b = 5.7431(2), c = 13.0107(5) Å, α = 98.772(2), β = 96.209(2), γ = 108.452(2)°, V = 378.71(2) Å3, and Z = 2. The crystal structure of dondoellite is characterized by isolated FeO4(H2O)2 octahedra that are linked by corner-sharing with PO4 tetrahedra to form so-called kröhnkite-type [Fe(PO4)2(H2O)2]2– chains along [100], similar to that observed in messelite. These chains are connected to one another by large Ca2+ cations and H bonds to form layers parallel to (001). The layers are further linked together by Ca–O and H bonds. However, unlike messelite, the crystal structure of dondoellite contains two symmetrically independent PO4 tetrahedra (P1O4 and P2O4) and two distinct CaO7(H2O) polyhedra (Ca1 and Ca2). The kröhnkite-type chains in dondoellite are constructed with P1O4 tetrahedra on one side and P2O4 tetrahedra on the other. Topologically, the dondoellite structure can be considered a combination of the collinsite and messelite structures alternating along [001], thus representing a new structure type for minerals with kröhnkite-type chains. The discovery of dondoellite raises the question as to whether polymorphs of fairfieldite, Ca2Mn2+(PO4)2·2H2O, or collinsite, Ca2Mg(PO4)2·2H2O, might also be found in nature.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.020 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".