Maruyamaite, K(MgAl <sub>2</sub> )(Al <sub>5</sub> Mg)Si <sub>6</sub> O <sub>18</sub> (BO <sub>3</sub> ) <sub>3</sub> (OH) <sub>3</sub> O, a potassium-dominant tourmaline from the ultrahigh-pressure Kokchetav massif, northern Kazakhstan: Description and crystal structure
Bibliographic record
Abstract
Maruyamaite, ideally K(MgAl 2 )(Al 5 Mg)Si 6 O 18 (BO 3 ) 3 (OH) 3 O, was recently approved as the first K-dominant mineral-species of the tourmaline supergroup. It occurs in ultrahigh-pressure quartzofeldspathic gneisses of the Kumdy-Kol area of the Kokchetav Massif, northern Kazakhstan. Maruyamaite contains inclusions of microdiamonds, and probably crystallized near the peak pressure conditions of UHP metamorphism in the stability field of diamond. Crystals occur as anhedral to euhedral grains up to 2 mm across, embedded in a matrix of anhedral quartz and K-feldspar. Maruyamaite is pale brown to brown with a white to very pale-brown streak and has a vitreous luster. It is brittle and has a Mohs hardness of ∼7; it is non-fluorescent, has no observable cleavage or parting, and has a calculated density of 3.081 g/cm 3 . In plane-polarized transmitted light, it is pleochroic, O = darkish brown, E = pale brown. Maruyamaite is uniaxial negative, ω = 1.634, ε = 1.652, both ±0.002. It is rhombohedral, space group R3m , a = 15.955(1), c = 7.227(1) Å, V = 1593(3) Å 3 , Z = 3. The strongest 10 X-ray dif- fraction lines in the powder pattern are [ d in Å( I )( hkl )]: 2.581(100)(051), 2.974(85)(1̄32), 3.995 (69)(2̄40), 4.237(59)(2̄31), 2.046(54)(1̄62), 3.498(42)(012), 1.923(36)(3̄72), 6.415(23)(1̄11), 1.595(22)(5̄.10.0), 5.002(21)(021), and 4.610(20)(030). The crystal structure of maruyamaite was refined to an R 1 index of 1.58% using 1149 unique reflections measured with Mo K α X-radiation. Analysis by a combination of electron microprobe and crystal-structure refinement gave SiO 2 36.37, Al 2 O 3 31.50, TiO 2 1.09, Cr 2 O 3 0.04, Fe 2 O 3 0.33, FeO 4.01, MgO 9.00, CaO 1.47, Na 2 O 0.60, K 2 O 2.54, F 0.30, B 2 O 3 (calc) 10.58, H 2 O(calc) 2.96, sum 100.67 wt%. The formula unit, calculated on the basis of 31 anions pfu with B = 3, OH = 3.24 apfu (derived from the crystal structure) and the site populations assigned to reflect the mean interatomic distances, is (K 0.53 Na 0.19 Ca 0.26 □ 0.02 ) ΣX=1.00 (Mg 1.19 Fe0.552+Fe0.053+${\rm{Fe}}_{0.55}^{2 + }{\rm{Fe}}_{0.05}^{3 + }$ Ti 0.14 Al 1.07 ) □Y=3.00 (Al 5.00 Mg 1.00 )(Si 5.97 Al 0.03 O 18 )(BO 3 ) 3 (OH) 3 (O0.602−${\rm{O}}_{0.60}^{2 - }$F 0.16 OH 0.24 ). Maruyamaite, ideally K(MgAl 2 ) (Al 5 Mg)(BO 3 ) 3 (Si 6 O 18 )(OH) 3 O, is related to oxy-dravite: ideally Na(MgAl 2 )(Al 5 Mg)(BO 3 ) 3 (Si 6 O 18 )(OH) 3 O, by the substitution X K → X Na.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.005 | 0.002 |
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 source (direct Gemma or distilled Codex), 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".