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Byline: Guibin Zhang (1,2), David J. Ellis (2), Andrew G. Christy (2), Lifei Zhang (1), Shuguang Song (1) Keywords: Rutile; Thermometry; Eclogite; Western China Abstract: Four Zr-in-rutile thermometry calibrations are applied to eclogites from Western China. Here, we show that if rutile grows in equilibrium with Qtz and Zrn, and is isolated inside garnet, it preserves its Zr composition and does not undergo compositional change due to cation exchange with the host garnet. It thus preserves the composition for the P--T conditions of its formation and the growth zoning of the host garnet. For the HP/UHP metamorphic temperature, the Tomkins et al. (J Metamorph Geol 25:703--713, 2007) calibration yields temperatures that agree well with previous studies, whereas the other three calibrations (Zack et al. in Contrib Mineral Petrol 148:471--488, 2004 Watson et al. in Contrib Mineral Petrol 151:413--433, 2006 Ferry and Watson in Contrib Mineral Petrol in 154:429--437, 2007), which do not include a pressure correction, give systematically lower temperatures. Zr contents of rutile inclusions within garnet show systematic decrease from garnet core to rim. The rutile inclusions in garnet rims contain the lowest Zr content, similar to that in the matrix. Analyses confirm that the pressure plays a significant role in modifying the primary temperature dependence of the Zr content of rutile. Rutiles trapped in garnets are unable to re-equilibrate easily during retrogression, but those in the matrix can do so, providing retrograde P--T path information. Author Affiliation: (1) MOE Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, 100871, Beijing, China (2) Research School of Earth Sciences, The Australian National University, Canberra, ACT, 0200, Australia Article History: Registration Date: 31/12/2009 Received Date: 24/06/2009 Accepted Date: 30/12/2009 Online Date: 13/01/2010 Article note: Communicated by T. L. Grove. Electronic supplementary material The online version of this article (doi: 10.1007/s00410-009-0486-2) contains supplementary material, which is available to authorized users.

Kapundaite, ideally [(Na,Ca).sub.2][Fe.sup.3+.sub.4][(P[O.sub.4]).sub.4] [(OH).sub.3] x 5[H.sub.2]O, is a new mineral (IMA2009-047) from Toms phosphate quarry, Kapunda, South Australia, Australia. The new mineral occurs as cavernous aggregates of fibers up to several centimeters across, associated with leucophosphite, natrodufrenite, and meurigite-Na crystals and amorphous brown, black, and/or greenish coatings. Individual kapundaite crystals are very thin flattened fibers up to a few millimeters in length, but typically no more than a few micrometers in thickness. The main form observed is {100}; other forms in the [010] zone are present, but cannot be measured. Crystals of kapundaite are pale to golden yellow, transparent to translucent, have a yellow streak and silky luster, and are non-fluorescent. Mohs hardness is estimated to be about 3; no twinning or cleavage was observed. Kapundaite is biaxial (+), with indices of refraction [alpha] = 1.717(3), [beta] = 1.737(3), and [gamma] = 1.790(3). 2V could not be measured; [2V.sub.cale] is 64.7[degrees]. The optical orientation is Z = b, Y [approximately equal to] c with weak pleochroism: X= nearly colorless, Y= light brown, Z = pale brown; absorption: Y> Z > X. No dispersion was observed. The empirical chemical formula (mean of seven electron microprobe analyses) calculated on the basis of 24 O is ([Ca.sub.1.13][Na.sub.0.95])[summation]2.08[([Fe.sup.3+.sub.3.83] [Mn.sub.0.03][Al.sub.0.02][Mg.sub.0.01]).sub.[summation]3.89] [P.sub.3.92][O.sub.16]([OH).sub.3] x 5[H.sub.2.11]O. Kapundaite is triclinic, space group P[bar.1], a = 6.317(5), b - 7.698(6), c = 9.768(7) [Angstrom], [alpha] = 105.53[(1).sup.o], [beta] = 99.24[(2).sup.o], [gamma] = 90.09[(2).sub.o], V = 451.2(6) [[Angstrom].sup.3], and Z- 1. The five strongest lines in the powder X-ray diffraction pattern are [[d.sub.obs] in [Angstrom], (I) (hkl)]: 9.338 (100) (001 ), 2.753 (64) (2[bar.1]1), 5.173 (52) (011 ), 2.417 (48) ([bar.2][bar.1]-3, 202, 0[bar.1]4), and 3.828 (45)(0[bar.2]1). The crystal structure was solved from single-crystal X-ray diffraction data using synchrotron radiation and refined to [R.sub.1] = 0.1382 on the basis of 816 unique reflections with [F.sub.o] > 4[sigma]F. The structure of kapundaite is based on a unique corrugated octahedral-tetrahedral sheet, which is composed of two types of chains parallel to a. Kapundaite is structurally related to melonjosephite. The mineral is named for the nearest town to the quarry. Keywords: Kapundaite, new mineral, phosphate, Toms phosphate quarry, crystal structure, octahedral-tetrahedral sheet, melonjosephite DOI: 10.2138/am.2010.3466

The open-branched tetrahedral chain of sapphirine-group minerals contains tetrahedra with 1-3 bridging O atoms ([Q.sup.1], [Q.sup.2], and [Q.sup.3]). The topology implies that short-range order (SRO) driven by bonding enthalpies forces some long-range order (LRO). This is an ideal system to investigate the interplay between SRO, LRO, and configurational entropy. Results are presented of Monte Carlo simulations of ordering patterns involving Be, Al, and Si on the branched chain. The 'Loewenstein's Rule' enthalpy term favoring AlOSi links is insufficient to obtain the experimental LRO occupancies. Additional site-dependent potentials repelling Si from [Q.sup.1] and [Q.sup.2] and driving asymmetry between the two [Q.sup.3] sites are needed. All enthalpy terms are close to 2 RT in magnitude, so the observed LRO cannot be regarded as arising dominantly from Si-avoidance. A 'Markov Braid' method is presented of calculating configurational entropies for the simulations. The substantial SRO present is shown to reduce [S.sub.config] by only 17-18%. Khmaralite is related to sapphirine but contains ca. 1.5 Be per 12 tetrahedra and shows different LRO of {Be, Al, Si}. The minority cation Be is concentrated in [Q.sup.3] sites. If the exchange enthalpy [DELTA][H.sub.AlSi] = -2 RT, then [DELTA][H.sub.BeAl] and [DELTA][H.sub.BeSi] must be -6.5 to -7.5 RT to reproduce the observed mean Q for Be, Al, and Si. Khmaralite has a doubled chain period relative to sapphirine. This superstructure enables the formation of tetrahedral Be-octahedral [Fe.sup.2+] clusters in the structure. A small number of site-specific potentials allows the LRO of the khmaralite chain to be reproduced, but 'Be-avoidance' remains by far the dominant interaction. Site occupancies were extrapolated to Be-rich compositions. More than 1.7 Be atoms per 12 tetrahedra is predicted to drive Be into new sites and create unfavorable BeOBe links, and to drive Si from [Q.sup.3] into the [Q.sup.1] sites. This is likely to be why the related mineral welshite, which can incorporate higher Be contents, has a quite different Be ordering pattern and symmetry. Keywords: Branched tetrahedral chain, khmaralite, sapphirine, welshite, aluminum, beryllium, silicon, aluminum avoidance, beryllium avoidance, configurational entropy, long-range order, Markov braid, short-range order, silicon avoidance

Apparent superlattice reflections obtained in electron diffraction patterns of modulated calcite and dolomite have been ascribed to local domains of various different metastable Ca-Mg ordering schemes that are not known as macroscopic phases. We show that the type 'c' reflections in diffraction patterns of supposed superstructures can in fact be produced by superposition of diffraction from the host crystal and that from domains that are in an orientation related to the host by twinning on (104). From details of the additional reflections present, we deduce that the carbonate anions are orientationally disordered in the twin nanodomains, which have the R[bar.3]m space group of high-temperature disordered calcite. This twinning can explain the diffraction ascribed to type '[gamma]'/'micro'/'v' superstructures, and resolves controversies over the occurrence of these purportedly different superstructures. The relationships between composition, orientational order of the carbonates, molar volume and known macroscopic structures, and the possibility of interracial strain reduction by static disorder in the twin domain, are discussed. We stress the importance of checking for presence of twinned nanodomains using microdiffraction before attributing an apparent superstructure modulation to local cation ordering. High-resolution imaging may not be diagnostic, since overlap of small domains and host matrix can give Moire patterns that resemble superlattice fringes. Keywords: Calcite, dolomite, twinning, superstructures, electron diffraction

From the first discovery in 1959 until the present, the abandoned Clear Creek mine has yielded an exceptional suite of rare and unusual mercury-bearing minerals unequaled in the world. Among [...]

A study was conducted on Al-Si ordering in natural and synthetic sapphirine crystals using magic-angle sample-spinning and high-resolution nuclear magnetic resonance. The Si environment was found to be similar for all samples of sapphirine crystals while the Al spectrum showed only one maximum peak. Intense peaks in the range of -73.1 were also observed in the Si spectra. Further observations showed that resolution decreased as the Si content increased, indicating a concomitant disorder increase in natural samples.