BORALSILITE AND Li,Be-BEARING “BORON MULLITE” Al<sub>8</sub>B<sub>2</sub>Si<sub>2</sub>O<sub>19</sub>, BREAKDOWN PRODUCTS OF SPODUMENE FROM THE MANJAKA PEGMATITE, SAHATANY VALLEY, MADAGASCAR
Bibliographic record
Abstract
Boralsilite Al16B6Si2O37 and Li,Be-bearing “boron mullite” Al8B2Si2O19 were discovered as breakdown products of spodumene from the elbaite-subtype Manjaka granitic pegmatite, Sahatany Valley, Madagascar. The pegmatite mineral assemblage is relatively simple (Ab + Qz > Kfs > Tur + Spd > Ap + several accessory B-rich phases). This pegmatite forms an E–W-trending elongated body emplaced in an Mg-rich calc-silicate rock; the pegmatite exocontact locally contains thin reaction zones (Tur+Phl±Brl). Boralsilite assemblages are closely associated with prismatic spodumene crystals, up to 10 cm long, mostly as narrow albite > K-feldspar zones (albite > K-feldspar > boralsilite > “boron mullite”), up to ∼0.5 mm thick, or rarely as inclusions in the central parts of spodumene crystals. Long prismatic crystals and fibers of boralsilite, up to 200 μm long, and rare elongated grains of “boron mullite” Al8B2Si2O19, up to 100 μm long, are mostly enclosed in albite and rarely in K-feldspar. The EMP and LA-ICP-MS data yielded relatively variable Al/Si ratios (∼5.4–9.8; ∼3.2–4.6) and concentrations of B (∼48500–59500; ∼24000–28000 ppm), Li (688–1433; 3339–4287 ppm), and Be (288–1082; 1017–2728 ppm), in boralsilite and “boron mullite”, respectively. Textural relations of the boralsilite assemblage assuming immobile Al suggest the hypothetical reaction: 46 LiAlSi2O6 + 30 Na+ (melt/aq.) + 6 H3BO3 = Al16B6Si2O37 + 30 NaAlSi3O8 + 46 Li+ (melt/aq.) + 9 H2O + 4 O2; part of the Li may have entered rare secondary clay minerals and partly also the “boron mullite”, but most of the Li was mobilized. Fluid/melt with very high a (B2O3), a (Na), and low a (H2O), along with high a (CO2) indicated by the absence of significant amount of hydrous phases, very minor extent of exocontact reactions along the pegmatite, and secondary rhodochrosite, are responsible for the origin of boralsilite. Very late solidus or early subsolidus conditions at temperature ∼350–450 °C and pressure ∼2–3 kbar, estimated for the crystallization of the assemblage albite + boralsilite, are significantly lower than those given for fibrous boralsilite at other localities of mostly anatectic granitic pegmatites (Larsemann Hills, Antarctica; Almgjotheii, Norway; and Horni Bory, Czech Republic).
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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 | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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 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".