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
Why this work is in the frame
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Bibliographic record
Abstract
© Walter de Gruyter Berlin/Boston 2016. Maruyamaite, ideally K(MgAl2)(Al5Mg)Si6O18(BO3)3(OH)3O, 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/cm3. 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) Å3, 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)(132), 3.995 (69)(240), 4.237(59)(231), 2.046(54)(162), 3.498(42)(012), 1.923(36)(372), 6.415(23)(111), 1.595(22)(5.10.0), 5.002(21)(021), and 4.610(20)(030). The crystal structure of maruyamaite was refined to an R1 index of 1.58% using 1149 unique reflections measured with MoKα X-radiation. Analysis by a combination of electron microprobe and crystal-structure refinement gave SiO2 36.37, Al2O3 31.50, TiO2 1.09, Cr2O3 0.04, Fe2O3 0.33, FeO 4.01, MgO 9.00, CaO 1.47, Na2O 0.60, K2O 2.54, F 0.30, B2O3(calc) 10.58, H2O(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 (K0.53Na0.19Ca0.26□0.02)ΣX=1.00(Mg1.19Fe0.552+Fe0.053+ Ti0.14Al1.07)□Y=3.00(Al5.00Mg1.00)(Si5.97Al0.03O18)(BO3)3(OH)3(O0.602 F0.16OH0.24). Maruyamaite, ideally K(MgAl2) (Al5Mg)(BO3)3(Si6O18)(OH)3O, is related to oxy-dravite: ideally Na(MgAl2)(Al5Mg)(BO3)3(Si6O18)(OH)3O, by the substitution XK → XNa.
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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 | 0.003 | 0.002 |
| Meta-epidemiology (narrow) | 0.006 | 0.005 |
| Meta-epidemiology (broad) | 0.006 | 0.002 |
| Bibliometrics | 0.001 | 0.003 |
| Science and technology studies | 0.004 | 0.009 |
| Scholarly communication | 0.003 | 0.004 |
| Open science | 0.005 | 0.003 |
| Research integrity | 0.003 | 0.004 |
| Insufficient payload (model declined to judge) | 0.000 | 0.001 |
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 it