Darrell J. Henry

Nomenclature of the tourmaline-supergroup minerals

Abstract A nomenclature for tourmaline-supergroup minerals is based on chemical systematics using the generalized tourmaline structural formula: XY3Z6(T6O18)(BO3)3V3W, where the most common ions (or vacancy) at each site are X = Na1+, Ca2+, K1+, and vacancy; Y = Fe2+, Mg2+, Mn2+, Al3+, Li1+, Fe3+, and Cr3+; Z = Al3+, Fe3+, Mg2+, and Cr3+; T = Si4+, Al3+, and B3+; B = B3+; V = OH1- and O2-; and W = OH1-, F1-, and O2-. Most compositional variability occurs at the X, Y, Z, W, and V sites. Tourmaline species are defined in accordance with the dominant-valency rule such that in a relevant site the dominant ion of the dominant valence state is used for the basis of nomenclature. Tourmaline can be divided into several groups and subgroups. The primary groups are based on occupancy of the X site, which yields alkali, calcic, or X-vacant groups. Because each of these groups involves cations (or vacancy) with a different charge, coupled substitutions are required to relate the compositions of the groups. Within each group, there are several subgroups related by heterovalent coupled substitutions. If there is more than one tourmaline species within a subgroup, they are related by homovalent substitutions. Additionally, the following considerations are made. (1) In tourmaline-supergroup minerals dominated by either OH1- or F1- at the W site, the OH1--dominant species is considered the reference root composition for that root name: e.g., dravite. (2) For a tourmaline composition that has most of the chemical characteristics of a root composition, but is dominated by other cations or anions at one or more sites, the mineral species is designated by the root name plus prefix modifiers, e.g., fluor-dravite. (3) If there are multiple prefixes, they should be arranged in the order occurring in the structural formula, e.g., “potassium-fluor-dravite.”

Titanium in biotite from metapelitic rocks: Temperature effects, crystal-chemical controls, and petrologic applications

Abstract An extensive natural biotite data set from western Maine constrains the temperature and crystalchemical controls on the saturation Ti levels in biotites from metapelites. The geologically and petrologically well-characterized metamorphic terrain associated with the M3 metamorphism of the Acadian Orogeny of western Maine is ideal for this approach in that metamorphism occurred at roughly isobaric conditions of 3.3 kbar, and chemical equilibrium was closely approached. The data set from these metapelites exhibits systematic variations in Ti contents over a continuum of metamorphic grades (garnet through sillimanite-K-feldspar zones), mineral assemblages, and bulk compositional ranges. Samples were selected so that competing substitutions are restricted to those in metapelites with quartz, aluminous phases (chlorite, staurolite, or sillimanite), Ti phases (ilmenite or rutile), and graphite. Due to crystal-chemical factors, in any given metamorphic zone, an inverse linear relationship exists between Ti and Mg contents. Decreasing octahedral Ti and increasing tetrahedral Si in Mg-rich biotite helps alleviate size disparity between octahedral and tetrahedral sheets. For a biotite with a given Mg content, Ti most dramatically increases above staurolite zone conditions. Our constrained data set allows us to calculate a Ti saturation surface for natural biotite as a function of temperature and Mg content at 3.3 kbar. The Ti saturation surface can be used to establish several important metamorphic features in similar metamorphic settings. These include a general approach to equilibrium, local and/or subtle departures from equilibrium due to minor alteration to chlorite, and relative and absolute geothermometry based on Ti in biotite inclusions in refractory minerals and in matrix biotite.

Tourmaline in a low grade clastic metasedimentary rock: an example of the petrogenetic potential of tourmaline

Detrital tourmaline grains and their associated tourmaline overgrowths provide a means to unravel the provenance and petrogenetic history of low grade clastic metasedimentary rocks. Evidence derives from tourmaline grains found in a lithic wacke metamorphosed to chlorite zone conditions. The detrital tourmaline cores are diagnostic indicators of the source rocks of the sediment whereas the overgrowths record both diagenetic and metamorphic reactions in the rock. Tourmaline grains consist of a detrital core surrounded by asymmetric overgrowths comprised of inner and outer rims. Abrupt chemical discontinuities between each of these zones implies that volume diffusion within tourmaline was minor under the conditions of formation. Compositions of the detrital cores vary widely, yet can be correlated with source rock types that are consistent with lithic fragments recognizable in the metawacke. At either the analogous or antilogous pole, inner rim compositions proximal to the detrital cores converge, despite the substrate tourmaline composition, indicating an approach to chemical equilibrium. However, significant dufferences in Al and X-site vacancies at the expense of Mg, Na and Ti between the analogous and antilogous poles of the inner rims demonstrate the presence of significant amounts of compositional polarity. Outer rim compositions at either pole also converge but compositional polarity between the analogous and antilogous poles persists. The presence of the inner and outer rims separated by a compositional discontinuity suggests punctuated evolution of the overgrowth. This implies that boron was sporadically available during diagenesis and metamorphism. Based on boron contents of minerals, this may correspond to a mechanism such as boron release due to polytypic change of illite or consumption of illite and/or muscovite. As such, tourmaline growth stages may serve as a monitor of chemical reactions in low grade metamorphic rocks.

Tourmaline-rich pseudomorphs in sillimanite zone metapelites: Demarcation of an infiltration front

The mineralogical community lost a valued colleague and friend with the death of Eugene E. Foord. Gene, a Life Fellow of the Mineralogical Society of America, died at his home on January 8, 1998 at the age of 51 after a three-year battle with lymphoma. Gene was a career scientist at the U.S. Geological Survey where he worked from 1976 until his death in 1998. Gene was an outstanding mineralogist and he will be remembered for his significant contributions to the mineralogy and paragenesis of pegmatites from San Diego County, California. He will also be remembered for his boundless enthusiasm for mineralogy, his dedication to thorough and accurate mineral identifications and descriptions, and his willingness to work with both professional scientists and amateur collectors. Foordite, a tin-niobium oxide was named after Gene ( ̌ Cerný et al. 1988) in honor of his many contributions to the study of niobium-tantalum-tin minerals in pegmatites. Gene enjoyed practical jokes, having learned from the master himself, Richard H. Jahns. In fact, Gene was the “mystery” person responsible for “relocating” the bust of Theodore Hoover from the third floor of the Stanford geology building. Gene was an enthusiastic and animated storyteller and he loved to entertain his friends and colleagues with his outrageously funny stories of his escapades including backyard bouts with birds, avoiding landmines along the Pakistan-Afghanistan border, finding stashes of frozen hummingbirds in a Stanford professor’s freezer, nearly “starving” to death in Labrador, graphic descriptions of the Russian cuisine, toying with guards while in house arrest in China, and many more. Gene was born at Children’s Hospital in Oakland, California, November 20, 1946. Gene, a RH-factor baby, had the distinction of being one of the first survivors of a complete exchange transfusion. However, as a result of the RH incompatibility, Gene was born severely hearing impaired. He moved in 1947 with his parents, Elizabeth and Delbert Foord, and his older brother William, to West Hempstead, New York. When his parents realized that Gene was hearing impaired, they took him to the Manhattan Eye and Ear Infirmary. They were told that their only education option was to enroll Gene in a special school for the deaf. However, his parents were determined to provide Gene with a normal education in their own hometown. Consequently, they joined together with other parents of hearing impaired children in Long Island and formed the Long Island Hearing and Speech Society. This was one of the first

Tourmaline in meta-evaporites and highly magnesian rocks: perspectives from Namibian tourmalinites

Tourmaline from meta-evaporitic tourmalinites of the Duruchaus Formation of central Namibia reveal a common compositional trend that occurs in tourmaline from other meta-evaporite localities. The meta-evaporitic tourmalines are generally sodic, magnesian, moderately-to-highly depleted in Al, and enriched in Fe 3+ and W O 2− (calculated). They typically follow this trend along a join between “oxy-dravite” [Na(Mg 2 Al)(Al 6 )(Si 6 O 18 )(BO 3 ) 3 (OH) 3 (O)] and povondraite [Na(Fe 3 3+ ) (Fe 4 3+ Mg 2 ) (Si 6 O 18 ) (BO 3 ) 3 (OH) 3 (O)]. Similar trends occur in the meta-evaporites at Alto Chapare (Bolivia), Challenger Dome (Gulf of Mexico), and Liaoning (China). This chemical feature is attributed to the influence of oxidizing, highly saline, boron-bearing fluids that are associated with these lithologies. In the Namibian tourmalines there are some deviations from this trend, which are considered to be a consequence of later overprints related to sulfate–silicate interactions and/or influx of reactive fluid. Tourmalines occurring in the highly magnesian high-pressure rocks (whiteschists and pyrope–coesite rocks) are distinctly more magnesian and fall close to the dravite and “oxy-dravite” compositions. These latter tourmaline compositions likely reflect the metasomatic processes that produced these unusual bulk compositions and/or the influx of a reactive fluid that eliminated any earlier chemical signatures of meta-evaporitic fluids or protoliths.

Compositional zoning and element partitioning in nickeloan tourmaline from a metamorphosed karstbauxite from Samos, Greece

Abstract Blue-green nickeloan tourmaline from a micaceous enclave of a marble from Samos, Greece, contains unusually high concentrations of Ni (up to 3.5 wt% NiO), Co (up to 1.3 wt% CoO), and Zn (up to 0.8 wt% ZnO). The polymetamorphic karstbauxite sample has an uncommon assemblage of nickeloan tourmaline, calcite, zincian staurolite, gahnite, zincohögbomite, diaspore, muscovite, paragonite, and rutile. The complex geologic history is reflected in multi-staged tourmaline growth, with cores that represent detrital fragments surrounded by two-staged metamorphic overgrowths. Zone-1 metamorphic overgrowths, which nucleated next to detrital cores, are highly asymmetric and exhibit compositional polarity such that narrow overgrowths of brown schorl developed at the (-) c-pole are enriched in Mg, Ti, and F, and depleted in Al, Fe, and X-site vacancies (x⃞ ) relative to wider, gray-blue schorl-to-foitite overgrowths developed at the (+) c-pole. Volumetrically dominant Zone-2 overgrowths are strongly zoned nickeloan dravites with a continuous increase in Mg, Co, Ca, and F at the expense of Fe, Zn, Cr, and V from the Zone-1 interface to the outermost rim. Within Zone 2, Ni reaches a maximum of 0.5 apfu before decreasing in the outer 20-40 µm. Zone-2 overgrowths also exhibit compositional polarity such that, at the (-) c-pole, overgrowths are enriched in Mg, F, Na, Ca, and Cr relative to overgrowths at the (+) c-pole that are, in turn, enriched in Al, Fe, Ni, Co, and X⃞ . Element partitioning involving tourmaline rims and coexisting minerals indicates that relative partitioning of Ni is tourmaline >> staurolite > gahnite; Co is tourmaline > staurolite > gahnite; and Zn is gahnite > staurolite >> tourmaline.

Metamorphic ultrahigh-pressure tourmaline: Structure, chemistry, and correlations to P-T conditions

Abstract Tourmaline grains extracted from rocks within three ultrahigh-pressure (UHP) metamorphic localities have been subjected to a structurally and chemically detailed analysis to test for any systematic behavior related to temperature and pressure. Dravite from Parigi, Dora Maira, Western Alps (peak P-T conditions ~3.7 GPa, 750 °C), has a structural formula of X(Na0.90Ca0.05K0.01⃞0.04) Y(Mg1.78Al0.99Fe2+0.12Ti4+0.03⃞0.08)Z(Al5.10Mg0.90)(BO3)3TSi6.00O18V(OH)3W[(OH)0.72F0.28]. Dravite from Lago di Cignana, Western Alps, Italy (~2.7-2.9 GPa, 600-630 °C), has a formula of X(Na0.84Ca0.09K0.01⃞0.06)Y(Mg1.64Al0.79Fe2+0.48Mn2+0.06Ti4+0.02Ni0.02Zn0.01)Z(Al5.00Mg1.00)(BO3)3T(Si5.98Al0.02)O18V(OH)3W[(OH)0.65F0.35]. “Oxy-schorl” from the Saxonian Erzgebirge, Germany (≥4.5 GPa, 1000 °C), most likely formed during exhumation at >2.9 GPa, 870 °C, has a formula of X(Na0.86Ca0.02K0.02⃞0.10)Y(Al1.63Fe2+1.23Ti4+0.11Mg0.03Zn0.01) Z(Al5.05Mg0.95)(BO3)3T(Si5.96Al0.04)O18V(OH)3W[O0.81F0.10(OH)0.09]. There is no structural evidence for significant substitution of [4]Si by [4]Al or [4]B in the UHP tourmaline ( distances ~1.620 Å), even in high-temperature tourmaline from the Erzgebirge. This is in contrast to high-T-low-P tourmaline, which typically has significant amounts of [4]Al. There is an excellent positive correlation (r2 = 1.00) between total [6]Al (i.e., YAl + ZAl) and the determined temperature conditions of tourmaline formation from the different localities. Additionally, there is a negative correlation (r2 = 0.97) between F content and the temperature conditions of UHP tourmaline formation and between F and YAl content (r2 = 1.00) that is best explained by the exchange vector YAlO(R2+F)-1. This is consistent with the W site (occupied either by F, O, or OH), being part of the YO6-polyhedron. Hence, the observed Al-Mg disorder between the Y and Z sites is possibly indirectly dependent on the crystallization temperature.

Coupled heat and silica transport associated with dike intrusion into sedimentary rock: effects on isotherm location and permeability evolution

An 11-meter-wide alkalic monchiquite dike recovered from the subsurface of Louisiana has produced a metasomatic aureole in the adjacent interbedded carbonate mudstones and siltstones. The asymmetric contact aureole, which extends nearly 6 m above and 4 m below the intrusion, contains the metamorphic minerals, diopside, pectolite, fluor-apophyllite, fluorite, and garnet. A series of coupled heat and mass transport calculations was undertaken to provide thermal constraints for the aureole, in the absence of robust geothermometric assemblages, and insights into accompanying mass transport associated with the sedimentary rock- dike system. Calculations were completed for systems with homogeneous, anisotropic, and layered permeability, . Transport, dissolution, and precipitation of silica were also incorporated into calculations. All systems modeled indicate that the thermal pulse waned in 3 yr with a return to background temperatures in 10 yr. Heat and fluid transport produce maximum temperature isotherms that are distinctly different in spatial extent and lateral variability for each numerical system. The homogeneous case produced isotherms that pinch and swell vertically above the dike and have large lateral variations, in contrast to the anisotropic case that produced a single large plume above the dike. The layered system case produced the most spatially extensive thermal aureole, unlike that recorded in the rocks. Addition of dissolved silica to the flow system significantly impacts the calculated transport of heat and fluid, primarily due to density changes that affect upwelling dynamics. Although precipitation and dissolution of SiO2 can affect flow through the feedback to permeability, changes were found to be minor for these system conditions. Where decreased, flow was refocused into higher zones, thus mitigating the differences over time. This negative feedback tends to defocus flow and provides a mechanism for lateral migration of plumes. Coupled heat and silica transport produces a complex isotherm geometry surrounding the intrusion due to formation of upwelling and downwelling plumes and lateral translation of plumes, leading to variability in the isotherm pattern that does not reflect the inherent heterogeneity of the initial material properties. Initial heterogeneities in are not a prerequisite for the development of a complicated flow and transport pattern. In addition, if isotherms reflect isograds, these calculations demonstrate that isograds may not form uniform structures with isograd boundaries characterized by their distance from the heat source. Copyright

Limitations of Fe2+ and Mn2+ site occupancy in tourmaline: Evidence from Fe2+- and Mn2+-rich tourmaline

Abstract Fe2+- and Mn2+-rich tourmalines were used to test whether Fe2+ and Mn2+ substitute on the Z site of tourmaline to a detectable degree. Fe-rich tourmaline from a pegmatite from Lower Austria was characterized by crystal-structure refinement, chemical analyses, and Mössbauer and optical spectroscopy. The sample has large amounts of Fe2+ (~2.3 apfu), and substantial amounts of Fe3+ (~1.0 apfu). On basis of the collected data, the structural refinement and the spectroscopic data, an initial formula was determined by assigning the entire amount of Fe3+ (no delocalized electrons) and Ti4+ to the Z site and the amount of Fe2+ and Fe3+ from delocalized electrons to the Y-Z ED doublet (delocalized electrons between Y-Z and Y-Y): X (Na0.9Ca0.1) Y(Fe2+2.0Al0.4Mn2+0.3Fe3+0.2) Z(Al4.8Fe3+0.8Fe2+0.2Ti4+0.1) T(Si5.9Al0.1)O18 (BO3)3V(OH)3W[O0.5F0.3(OH)0.2] with a = 16.039(1) and c = 7.254(1) Å. This formula is consistent with lack of Fe2+ at the Z site, apart from that occupancy connected with delocalization of a hopping electron. The formula was further modified by considering two ED doublets to yield: X(Na0.9Ca0.1) Y(Fe2+1.8Al0.5Mn2+0.3Fe3+0.3) Z(Al4.8Fe3+0.7Fe2+0.4Ti4+0.1) T(Si5.9Al0.1)O18 (BO3)3V(OH)3W[O0.5F0.3(OH)0.2]. This formula requires some Fe2+ (~0.3 apfu) at the Z site, apart from that connected with delocalization of a hopping electron. Optical spectra were recorded from this sample as well as from two other Fe2+-rich tourmalines to determine if there is any evidence for Fe2+ at Y and Z sites. If Fe2+ were to occupy two different 6-coordinated sites in significant amounts and if these polyhedra have different geometries or metal-oxygen distances, bands from each site should be observed. However, even in high-quality spectra we see no evidence for such a doubling of the bands. We conclude that there is no ultimate proof for Fe2+ at the Z site, apart from that occupancy connected with delocalization of hopping electrons involving Fe cations at the Y and Z sites. A very Mn-rich tourmaline from a pegmatite on Elba Island, Italy, was characterized by crystal-structure determination, chemical analyses, and optical spectroscopy. The optimized structural formula is X(Na0.6□0.4) Y(Mn2+1.3Al1.2Li0.5) ZAl6TSi6O18 (BO3)3V(OH)3 W[F0.5O0.5], with a = 15.951(2) and c = 7.138(1) Å. Within a 3σ error there is no evidence for Mn occupancy at the Z site by refinement of Al ↔ Mn, and, thus, no final proof for Mn2+ at the Z site, either. Oxidation of these tourmalines at 700-750 °C and 1 bar for 10-72 h converted Fe2+ to Fe3+ and Mn2+ to Mn3+ with concomitant exchange with Al of the Z site. The refined ZFe content in the Fe-rich tourmaline increased by ~40% relative to its initial occupancy. The refined YFe content was smaller and the distance was significantly reduced relative to the unoxidized sample. A similar effect was observed for the oxidized Mn2+-rich tourmaline. Simultaneously, H and F were expelled from both samples as indicated by structural refinements, and H expulsion was indicated by infrared spectroscopy. The final species after oxidizing the Fe2+-rich tourmaline is buergerite. Its color had changed from blackish to brown-red. After oxidizing the Mn2+-rich tourmaline, the previously dark yellow sample was very dark brown-red, as expected for the oxidation of Mn2+ to Mn3+. The unit-cell parameter a decreased during oxidation whereas the c parameter showed a slight increase.

The F-analogue of schorl from Grasstein, Trentino - South Tyrol, Italy : crystal structure and chemistry

The F-analogue of schorl has been identified in samples from a pegmatite at Grasstein, Trentino-South Tyrol, Italy. The crystal chemistry of this tourmaline has been characterized by a combination of single-crystal structure refinement, chemical analysis, and Mossbauer spectroscopy, yielding the structural formula X (Na 0.78 K 0.01 □ 0.2l ) Y (Fe 2+ 1.89 Al 0.58 Fe 3+ 0.13 Mn 2+ 0.13 Ti 4+ 0.02 Mg 0.02 Zn 0.02 □ 0.21 ) Z (Al 5.74 Fe 3+ 0.26 ) T (Si 5.90 Al 0.10 O 18 ) (BO 3 ) 3 V (OH) 3 W [F 0.76 (OH) 0.24 ]; a = 15.997(2), c = 7.179(1) A, V = 1591.0(4) A 3 , R 1( F ) = 1.60 %. This F-rich and Fe 2+ -rich tourmaline, a pneumatolytic phase crystallized in the presence of a F-rich fluid (coexisting with fluorite), is very near the proposed end-member composition of the F-analogue of schorl: NaFe 3 2+ Al 6 Si 6 O 18 (BO 3 ) 3 (OH) 3 F. The relatively high amount of Fe 2+ at the Y site is consistent with the large distance of 2.056 A. Refinement ofthe F:O occupancy ratio at the W site yields F 0.8 O 0.2 pfu, consistent with the chemical data (F 0.76 apfu). Because ofthe local bonding ofthe W -site anion to three neighbouring Y -site cations and the X -site cation, the charge of the X-site cation should affect the F occupancy at the W site. The cation and anion occupancy of this tourmaline is consistent with observations that tourmalines not dominated by X -site vacancies can have high F concentrations in the W site if F is present in the coexisting fluid phase. It is thus likely that the occurrence of high amounts of F in Fe-rich tourmalines requires a significant percentage of Fe 3+ in the tourmaline structure.