Boron adsorption by Ca forms of montmorillonite, illite, and kaolinite was determined as a function of pH and boron concentration in solution. Data from batch experiments were compared with results computed for each clay according to fitted adsorption coefficients (maximum boron adsorption and affinity constants related to the binding energy). The agreement between calculated values and experimental results indicates that a phenomenological equation can be used to predict boron adsorption on clays as a function of both of these variables. For the solution-to-clay ratios examined, the water content does not affect the boron-surface interaction as expressed by the above adsorption parameters. Because the affinity of clays for B(OH)4− is much stronger than for B(OH)3 , the adsorption maximum was obtained only under alkaline conditions at approximately pH 9.0 to 9.7. It is suggested that the pH of maximum adsorption is a function of the ratios of affinity coefficients of the three species B(OH)3, B(OH)4−, and OH− competing for the same adsorption sites. The adsorption coefficients indicate that in some cases the difference in the amount of adsorbed boron between montmorillonite and kaolinite could be either small or large, depending on the circumstances. The main factor that would affect this difference is the total amount of boron in the suspension. Estimated value of the adsorption maximum was 2.94, 11.8 and 15.1 µmole/g for Ca-kaolinite, Ca-montmorillonite, and Ca-illite, respectively.

An assemblage of clay minerals, Na-zeolites, Fe- and Sb-sulfides, and borates occurs in cavities in the basalt flow that underlies the main borax ore body exposed by the U.S. Borax open pit at Boron, Kern County, California. Analcime and saponite are widespread in cavities and fractures near the top of the basalt. Part of the basalt recently exposed, although restricted in distribution, contains a much more diverse assemblage of diagenetic minerals. Although only a few different minerals occur in each cavity, the composite order of deposition is: ferroan saponite, pyrrhotite, saponite, phillipsite, gmelinite, clinop-tilolite, herschelite, analcime, greigite, rhodochrosite, searlesite, borax, calcite, and colemanite. In some cavities early-formed zeolites appear to have dissolved as later ones crystallized.

Microprobe analyses of the zeolites yielded the following compositions: phillipsite, Na4.28K0.08(Al4.36-Si11.64O32)·xH2O (Si/Al = 2.67); gmelinite, Na6.64K0.10(Al6.80Si17.22O48· xH2O (Si/Al = 2.53); herschelite, Na2.96K0.24(Al3.21Si8.79O24)· xH2O (Si/Al = 2.75); clinoptilolite, Na6.48K0.56(Al7.15Si28.77O72) · xH2O (Si/Al = 4.02); analcime, Na14.02K0.09(Al13.33Si34.44O96)· xH2O (Si/Al = 2.58).

These zeolites formed by reactions between the basalt and evolving fluids, which were controlled by the development of an overlying, Na-borate lake. The wide distribution of saponite, analcime, and searlesite suggests that these minerals formed by the diagenetic reaction between basaltic glass and Na- borate water. The localized occurrence of the complex mineral assemblage, including some of the saponitic clay and the zeolites, phillipsite, gmelinite, and clinoptilolite, formed through a different process, perhaps deuteric or hydrothermal alteration of the basalt, before the lake developed. Because these zeolites are extraordinarily rich in Na, cation exchange may have taken place as the pore fluids became increasingly Na rich. In the latest stages of mineral growth, each of these zeolites was apparently partially dissolved and epitaxially overgrown by a second generation crystal, phillipsite on phillipsite, herschelite on gmelinite, and sodian heulandite on clinoptilolite.

The effects of exchangeable Na and Ca and the ionic strength of NaCl and CaCl2 solutions on the boron adsorption by the Na and Ca forms of montmorillonite and illite at pH 9 were studied. The boron adsorption by montmorillonite was greater for the Ca form than for the Na form at any boron activity in solution and at any ionic strength. For example, the amount of boron adsorbed by Na- and Ca-montmo-rillonite was 2.9 and 4.3 μmole/g, respectively, at an ionic strength of 0.36 and a boron activity of 0.875 mmole/liter in equilibrium solution. The boron adsorption by illite was much greater than by montmorillonite. For example, the amount of boron adsorbed by Na-montmorillonite and Na-illite was 1.5 and 8.7 μmole/g, respectively, at an ionic strength of 0.02 and a boron activity of 0.5 mmole/liter. However, the nature of the exchangeable cation had little effect on the boron adsorption by illite. The effect of the ionic strength on the boron adsorption by Na-montmorillonite was greater than that observed for either Camontmorillonite or illite. The data suggest that the negative electric field around the clay particles is one of the main factors controlling boron adsorption at alkaline pHs.

Boron adsorption on 2-0.2-μm size fractions of kaolinite at 25° ± 2°C at pH values between 6.0 and 10.5 was studied. The kaolinite sample was pretreated to remove any surface oxide and hydroxide coatings. The initial concentrations of boron in solution ranged between 2 and 10 mg/liter with either KClO4 or Ca(ClO4)2 as background electrolyte at constant ionic strength of 0.09 ± 0.01 mole/liter. Boron speciation in equilibrium solutions was calculated by using the chemical equilibrium computer program GEOCHEM. The adsorption of boron on kaolinite in either medium showed similar dependence on pH and initial boron concentrations. Boron adsorption at higher pHs was noticeably higher in Ca(ClO4)2 medium as compared to KClO4 medium. These differences were attributed to the formation and adsorption of CaB(OH4)+ ion-pair species.

Boron sorption by hydrous Al-oxide was studied as a function of concentration, pH, temperature and in the presence of oxalate and phosphate. For comparison sorption of B was also measured with charcoal as adsorbent.

At constant pH a Langmuir type equation was found to fit the results well at pH values below 7.2 where only boric acid molecules are present in solution. B sorption was dependent on pH with maximum sorption at pH 8.5. Oxalate and phosphate ligands form strong bonds to AI and were found to reduce B sorption. Sorption of boric acid molecules decreased with increasing temperature and the isosteric heat of reaction was 13.8 kJ mol−1. These results indicate that there are two mechanisms of sorption on hydrous Al-oxide, physical sorption of boric acid molecules and ligand exchange (chemisorption) of borate, and both mechanisms are favored onto the oxide.

Boron adsorption at constant ionic strength [0.09 ± 0.01 moles/liter of KClO4 or Ca(ClO4)2] on 0.2−2 μm clay fraction of pretreated kaolinite was modeled using both phenomenological equations and surface complexation reactions. Phenomenological equations were expressed as linear relationships between the distribution coefficient and adsorption density or equilibrium concentration. The normalized form of the isotherms allowed the distribution coefficient to be predicted over a wide range of adsorption densities or equilibrium concentrations and pH. The Langmuir isotherm revealed a weak two-part linear trend supported by a similar behavior of the van Bemmelen-Freundlich isotherm. Potential adsorption mechanisms were assessed from these isotherms. The bases for the inner-sphere (surface coordination) and outer-sphere (ion-pair) surface reactions were postulated, and equations were developed and incorporated into the generalized triple-layer surface-complexation model [TL(g)-SCM]. Boron adsorption was best modeled using the inner-sphere complexes. The results confirm that the generalized triple-layer surface-complexation model can provide information regarding plausible reactions at the substrate/aqueous interface. Intrinsic constants for postulated surface reactions were derived as fitting parameters over a range of pH and initial boron concentrations.

The incorporation of boron (B) and nitrogen (N) into illite is the key demand-side process responsible for the diagenetic budget of these elements in sedimentary basins, with important implications for pore-water chemistry, natural-gas composition, and borehole geophysics. The purpose of the present study was to take advantage of recent advances in quantitative mineral analysis of sedimentary rocks which have opened new possibilities for investigating this particular process. In order to avoid complications with recycled (detrital) N and B, clays from pyroclastic horizons of sedimentary rocks (bentonites) were used. The B and N contents in illite-smectite were measured in samples from different sedimentary basins, representing a complete range of diagenetic alteration. The bulk-rock chemical measurements, performed on raw rock samples in order to avoid any loss of exchangeable B and N, were referred to the contents of illite-smectite clays and to the content of illite alone, both measured by a combination of XRD and chemistry-based techniques.

Both B and N (as NH4) are present in illite, so their contents in illite-smectite clay increase in a more or less linear manner with progressing illitization. Thus, during diagenesis, the illite-smectite clay is a net consumer of B and N from the pore water. The amount of N in individual illite layers decreases during diagenesis and the amount of B either decreases or remains stable. Bentonitic illite must acquire both B and N from outside of the bentonite bed. In one diagenetic cycle, bentonitic illite fixes up to 800–1000 ppm B and up to >1% N expressed as (NH4)2O, corresponding to >20% of the fixed cation sites.

Differences in equilibration rates among crystals of different sizes may be used to deduce paleofluid changes over time if the crystal-growth mechanism is known. To explore isotopic equilibration rates as a function of illite growth, we studied B-isotope changes during illitization of smectite. Montmorillonite (<2.0 µm SWy-1, K saturated) was reacted with aqueous boric acid (1000 ppm B) at 300°C, 100 MPa in sealed Au capsules (1:1 fluid:mineral ratio). The initial fluid was 0‰ (NBS 951 standard) but after R1 ordering occurred (65 days of reaction) the fluid was changed to −7‰ in order to examine the rate of isotopic re-equilibration. Samples were taken intermittently throughout the experiment. Each aliquot was NH4 exchanged and size separated into fine (<0.2 µm), medium (0.2–2.0 µm) and coarse (>2.0 µm) fractions. The isotopic composition of B in the tetrahedral sheet was then measured for comparison with the predicted equilibrium values.

The fine fraction showed equilibrium isotope ratios within 10 days, indicating that small, newly nucleated crystals precipitate in equilibrium with the fluid under supersaturated, closed conditions. These fine-fraction minerals did not re-equilibrate when the fluid was changed. The medium fraction gradually equilibrated with the initial fluid as illite grew to values >50%, but did not re-equilibrate with the later fluid. The coarse fraction was slow to begin recrystallization, perhaps due to dissolution kinetics of large crystals or the presence of detrital contaminants. However, it showed the fastest rate of isotopic change with crystal growth after R1 ordering. We conclude that at 300°C, the initial B–O bonds formed in illite are stable, and isotopic re-equilibration only occurs on new crystal growth. Therefore, different isotope ratios are preserved in different crystal size fractions due to different rates of crystal growth. Large crystals may reflect equilibrium with recent fluid while smaller crystals may retain isotope compositions reflecting equilibrium with earlier fluids.

Boron has been shown to be a useful trace element in clay-mineralization reactions, raising the possibility that B studies may provide a means to investigate environmental controls on palagonitization. The objective of the present study was to address calibration, matrix effects, and B exchangeability issues such that meaningful secondary ion mass spectrometry (SIMS) microanalysis of B in thin sections of palagonite will be feasible. Silver Hill illite (IMt-1) was found to be a suitable calibration reference material, based on compositional similarity, relatively high B content, and ease of mounting on thin-section samples for SIMS microanalysis. Matrix effects of borated sideromelane and illite were compared and found to be similar, confirming previous studies which showed no matrix effects for B among minerals. Boron substitutes for Si in tetrahedral sites and also can be adsorbed in exchangeable sites of 2:1 clay minerals. Similarly, B can be found in tetrahedral and exchangeable sites within palagonite, which consists of both layered and amorphous volumes. In order to measure tetrahedral B content and isotopic ratio in the palagonite, exchangeable B was removed by soaking sample thin sections in a 1 M NH4Cl solution until exchangeable cation concentrations were constant. Treated samples showed decreases in B content and isotopic ratio with exchange. Extraction of exchangeable B permits the direct measurement of tetrahedral B content and isotopic ratio. The exchange technique devised and tested here should have broad applicability to thin-section microanalysis of B in clay and clay-like materials where cation exchange can be used for surface-analytical techniques. The present study represents an initial attempt to address samplepreparation, calibration, and potential matrix-effects problems for analyses by SIMS. Further refinements may improve the accuracy of the measurements, but the results presented here indicate that meaningful measurements are possible.

TiAl alloys are potential structural high-temperature structural materials at a service temperature of ~900 °C, while poor ductility at room temperature and high creep rate at the elevated temperature limits the applications. To improve the room-temperature and high-temperature mechanical properties of Ti–44Al–5Nb–3Cr–1.5Zr, Mo and B were introduced into this system and Ti–44Al–5Nb–3Cr–1.5Zr–xMo–yB alloys were proposed. And then, we, respectively, studied the microstructures and mechanical properties of Ti–44Al–5Nb–3Cr–1.5Zr–xMo–0B and Ti–44Al–5Nb–3Cr–1.5Zr–1Mo–yB to elucidate the role for the addition of Mo and B. It is found that Mo can increase the fraction of B2 phase in the alloys and the microstructures of the alloys are greatly refined by the addition of B. The compression test results indicate that Mo has a positive influence on the high-temperature compressive properties of TiAl-based alloys, whereas B addition can improve their room-temperature compressive properties of Ti–44Al–5Nb–3Cr–1.5Zr–1Mo–yB alloys; the morphology of borides in each sample should be the structural origin for these phenomena.

The determination of low boron concentrations in silicate glasses by electron probe microanalysis (EPMA) remains a significant challenge. The internal interferences from the diffraction crystal, i.e. the Mo-B4C large d-spacing layered synthetic microstructure crystal, can be thoroughly diminished by using an optimized differential mode of pulse height analysis (PHA). Although potential high-order spectral interferences from Ca, Fe, and Mn on the BKα peak can be significantly reduced by using an optimized differential mode of PHA, a quantitative calibration of the interferences is required to obtain accurate boron concentrations in silicate glasses that contain these elements. Furthermore, the first-order spectral interference from ClL-lines is so strong that they hinder reliable EPMA of boron concentrations in Cl-bearing silicate glasses. Our tests also indicate that, due to the strongly curved background shape on the high-energy side of BKα, an exponential regression is better than linear regression for estimating the on-peak background intensity based on measured off-peak background intensities. We propose that an optimal analytical setting for low boron concentrations in silicate glasses (≥0.2 wt% B2O3) would best involve a proper boron-rich glass standard, a low accelerating voltage, a high beam current, a large beam size, and a differential mode of PHA.

The evolution of the nitrogen and boron content of shales during diagenesis and anchimetamorphism was studied in the Carboniferous rocks of Donbas by means of the bulk rock chemical analysis and the XRD quantification of mineral composition, aided by CEC and EGME sorption measurements. The contributions of the organic-bound N and B were taken into account, based on the literature data (B) and on the relationship established in the course of this study (N). 28–98% of the total N and 80–100% of the total B are contained in the mineral fraction of the investigated shales.

The mineral nitrogen is located mostly in illite and accounts for 3 to 64% of the sites available for its fixation in 1Md illite. The fixation of N by illite seems to diminish in the course of diagenesis, but additional fixation occurs in newly formed 2M1 illite during the anchimetamorphic stage. The volume of N contained in illite in most samples greatly surpasses the N available locally from the organic matter contained in shale. Modelling indicates that the measured level of N for K substitution in illite corresponds to the capture in 30 vol.% of shale of all N released in a basin containing 5 vol.% of coal.

Boron is held predominantly by the 1Md fraction (illite+smectite). During diagenesis boron is redistributed into the 1Md illite, and during anchimetamorphism it is released from the 1Md illite and incorporated into new 2M1 illite. No indication of the net enrichment of pore water in B due to the clay alteration process was found.

Nearly boron-free kornerupine is locally abundant in pods or lenses of coarse-grained, non-foliated, Mg- and Al-rich rocks that occur at high metamorphic grades in early Proterozoic metapelitic rocks from the Reynolds Range, Northern Territory, Australia. This is the third reported occurrence of boron-free kornerupine worldwide. The samples consist almost entirely of coarse-grained kornerupine and its breakdown products sapphirine, cordierite, and gedrite or orthopyroxene. The kornerupine contains only 0.45 wt.% B2O3, corresponding to 0.098 B atoms per 22 (O, OH), and closely approximates 11:10:11 in terms of molar ratios of (MgO + FeOtotal):Al2O3:SiO2, with XMg = Mg/(Mg + Fetotal) = 0.874. The unusual textures and bulk compositions of the rocks in the pods are interpreted to have resulted from metasomatism and high-grade metamorphism (750 to 800° and ∼ 4.5 kbar) of precursors that may have included sedimentary Mg-rich clays. Rocks containing boron-poor, and relatively boronrich kornerupine (2.18 wt.% B2O3; XMg = 0.892) are separated in outcrop by as little as 10 m of the foliated cordierite-quartzite country rock and other rock types, suggesting that the compositions or amounts of the metasomatic fluids varied on a local scale.

Accessory tourmaline in metasediments from the Sinai crystalline basement exhibits textural and chemical signatures that relate to the evolution of regional metamorphism and deformation during the Pan-African orogeny and testifies to different P-T path segments. Tourmaline inclusions in various porphyroblasts were formed during the prograde phase of metamorphism; acicular to prismatic crystals in the matrix, oriented sub-parallel to, and enveloped by, the main foliation crystallized syntectonically under prograde and peak metamorphic conditions; tourmaline cross-cutting the main foliation may have formed just after the peak or during the retrograde phase of metamorphism. Some of the cores in tourmaline crystals, showing different colours, are interpreted as former detrital grains. The abundance of tourmaline decreases with increasing peak metamorphic conditions. The tourmaline investigated belongs to the schorl-dravitess group, generally with XMg of 0.42–0.73 and XCa = Ca/(Ca+Na+K+□) of 0.02–0.24, typical of tourmalines in metapelites and metapsammites; whereas detrital cores have been derived from various sources, including former tourmaline-quartz and pre-existing high-metamorphic rocks. Tourmaline of the Sinai metasediments was formed during metamorphism of the sedimentary precursors, essentially in a closed system, where clay minerals and organic matter, together with detrital tourmaline, served as the source of boron. Although a metamorphic facies should be defined by characteristic mineral assemblages present in metamorphic rocks, tourmaline chemistry is a good monitor of P-T conditions in the metapelites and semi-metapelites investigated, showing an increase in XMg with increasing metamorphic grade, where XturMg = 0.60 distinguishes between greenschist and lower-amphibolite facies, while XturMg = 0.65 could distinguish lower- from middle- to upper-amphibolite facies. The results of tourmaline-biotite geothermometry compare well with our former temperature estimates using conventional geothermometry and phase-diagram modelling.

The study focuses on the distribution of B, Be, Li, rare earth elements (REE), high-field-strength elements (HFSE), Th, U and Pb in fresh and hydrothermally altered ocean island basalts (OIB) from French Polynesia, and evaluates B/Be and Li/Be ratios as potential tracers of subducted components in the mantle. Hydrothermal solutions affecting the rocks during cooling were derived from meteoric water, sea water and magmatic fluids. The concentrations of REE, HFSE, Th and Be in the OIB were not affected by secondary processes except during advanced stages of subaerial hydrothermal alteration where saponite was a dominant secondary phase. This alteration modified the contents of these elements, changed REE patterns and produced a positive Ce anomaly. The subaerial and submarine hydrothermal alteration (T ∼ 70–100°C) may change U concentrations in OIB, whereas Pb was only marginally redistributed during alteration.

Boron was enriched during submarine and subaerial hydrothermal alteration but was not noticeably affected in basalts altered by magmatic fluids at T > 200°C. Like B, the mobility of Li during the alteration varies with fluid temperature. Lithium became enriched in the basalts during advanced stages of lower T hydrothermal alteration (<100°C). However, this element was partly removed from the rocks during higher T alteration (>200°C) by magmatic fluids. Boron, Be and Li behave as incompatible trace elements in basaltic magmas. Beryllium content in primitive mantle is estimated to be 0.07 ppm. Fresh Polynesian OIB have low abundances of B and Li and low B/Be (2–5) and Li/Be (2.5–5) ratios compared with volcanic arc rocks, marine sediments and altered oceanic crust. Various OIB including even those which have HIMU- and EM-affinities have similar overlapping B/Be and Li/Be ratios. Both B and Li are probably stripped from a lithospheric slab during subduction-related metamorphism and are, thus, not involved in deep mantle recycling. The mantle-normalized trace element abundances of MORB and OIB usually display patterns characterized by negative B, Pb and Li anomalies. The patterns of continental crust and crustal rocks have distinct positive anomalies for these elements whereas continental basaltic rocks have variable relative abundances of B, Pb and Li. The anomalies of these elements in basalts can be useful in discriminating their tectonic setting and constraining the mantle source regions of basalts.

In 1884, Lorenzen proposed the formula MgAl2SiO6 for his new mineral kornerupine from Fiskenæsset and did not suspect it to contain boron. Lacroix and de Gramont (1919) reported boron in Fiskenæsset kornerupine, while Herd (1973) found none. New analyses (ion microprobe mass analyser and spectrophotometric) of kornerupine in three specimens from the type locality, including the specimens analysed by Lorenzen and Herd, indicate the presence of boron in all three, in amounts ranging from 0.50 to 1.44 wt.% B2O3, e.g. (Li0.04 Na0.01 Ca0.01) (Mg3.49 Mn0.01 Fe0.17 Ti0.01 Al5.64)Σ9.30 (Si3.67 Al1.02 B0.31)Σ5 O21 (OH0.99 F0.01) for Lorenzen's specimen. Textures and chemical compositions suggest that kornerupine crystallized in equilibrium in the following assemblages, all with anorthite (An 92–95) and phlogopite (XFe = atomic Fe/(Fe + Mg) = 0.028–0.035): (1) kornerupine (0.045)-gedrite (0.067); (2) kornerupine (0.038–0.050)-sapphirine (0.032–0.035); and (3) kornerupine (0.050)-hornblende. Fluorine contents of kornerupine range from 0.01 to 0.06%, of phlogopite, from 0.09 to 0.10%. In the first assemblage, sapphirine (0.040) and corundum are enclosed in radiating bundles of kornerupine; additionally sapphirine, corundum, and/or gedrite occur with chlorite and pinite (cordierite?) as breakdown products of kornerupine. Kornerupine may have formed by reactions such as: gedrite + sapphirine + corundum + B2O3 (in solution) + H2O = kornerupine + anorthite + Na-phlogopite under conditions of the granulite facies. Boron for kornerupine formation was most likely remobilized by hydrous fluids from metasedimentary rocks occurring along the upper contact of the Fiske⇒set gabbro-anorthosite complex with amphibolite.

Okayamalite, Ca2B2SiO7, tetragonal, P21m, a = 7.116, c = 4.815 Å, Z = 2, is a new member of melilite group, the boron analogue of gehlenite. Electron microprobe analysis gave CaO 46.28, B2O3 28.50, SiO2 24.24, Al2O3 0.36, total 99.38 wt.%, corresponding to Ca2.01B2.00Si0.98Al0.02O7, a natural counterpart of Ca2B2SiO7 known only synthetically. The strongest lines in the X-ray powder diffraction pattern are 3.479 (40)(111), 2.862 (55)(201), 2.654 (100)(211), 2.129 (20)(301), 1.920 (35)(212), 1.644 (29)(312), very close to those of the synthetic material (a = 7.115, and c = 4.812 ). It is creamy white in colour with an earthy appearance due to the fine grain size. Streak white, cleavage not observed. Hardness ∼5½. Density calculated on the ideal formula is 3.30 g/cm3. It is optically uniaxial negative with ω = 1.700, and ɛ = 1.696. It occurs as patches of a few millimetres across in grey homogeneous-looking aggregate of wollastonite, vesuvianite, calcite and johnbaumite from Fuka mine, Bicchu-cho, Okayama Prefecture, Japan. The patches consist of very fine grains of the mineral up to 30 μm. Okayamalite is considered to be a product after the reaction formula: CaCO3 + CaSiO3 + B2O3 = Ca2B2SiO7 + CO2, arising from boron metasomatism of a wollastonite-calcite aggregate. The name is for the prefecture.

Kornerupine and prismatine were introduced independently by Lorenzen in 1884 (but published in 1886 and 1893) and by Sauer in 1886, respectively. Ussing (1889) showed that the two minerals were sufficiently close crystallographically and chemically to be regarded as one species. However, recent analyses of boron using the ion microprobe and crystal structure refinement, indicate that the boron content of one tetrahedral site in kornerupine ranges from 0 to 1. Kornerupine and prismatine, from their respective type localities of Fiskenæsset, Greenland and Waldheim, Germany, are distinct minerals, members of an isomorphic series differing in boron content. For this reason, we re-introduce Sauer’s name prismatine for kornerupines with B > 0.5 atoms per formula unit (p.f.u.) of 22(O,OH,F), and restrict the name kornerupine sensu stricto to kornerupines with B < 0.5 p.f.u. Kornerupine sensu lato is an appropriate group name for kornerupine of unknown boron content. Kornerupine sensu stricto and prismatine from the type localities differ also in Fe2+/Mg ratio, Si − (Mg + Fe2+ + Mn) content, Al content, F content, colour, density, cell parameters, and paragenesis. Both minerals formed under granulite-facies conditions with sapphirine and phlogopite, but kornerupine sensu stricto is associated with anorthite and hornblende or gedrite, whereas prismatine is found with oligoclase (An9–13), sillimanite, garnet, and/or tourmaline. Occurrences at other localities suggest that increasing boron content extends the stability range of prismatine relative to that of kornerupine sensu stricto.