Basement rocks of Santorini have been locally impregnated by iron oxides and other minerals. The hydrothermal fluids which caused the mineralization have extensively altered the impregnated rocks, but left granditic garnets in these unaffected.

Mössbauer spectroscopy and differential X-ray diffraction show that the iron oxides present are goethite and hematite in a ratio of about 2 : 1. The presence of hematite indicates that these minerals formed, directly from a hydrothermal phase, at higher temperatures than the recent submarine iron oxide deposits of Santorini, which contain no hematite.

Coquimbite, AlFe3+3(SO4)6(H2O)12⋅6H2O, was considered as a pure Fe3+ hydrated sulfate. However, previous mineralogical studies pointed out the occurrence of essential Al, occupying a distinct site in the crystal structure of this mineral. Through the critical re-examination of the available literature and new crystal-chemical data collected on a specimen from the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy, the chemical formula of coquimbite has been revised, taking into account the occurrence of Al. Coquimbite has a homeotypic relationship with paracoquimbite, Fe4(SO4)6(H2O)12⋅6H2O; both mineral species belong to the coquimbite group. On the contrary, aluminocoquimbite, Al2Fe2(SO4)6(H2O)12⋅6H2O, has a different topology and does not belong to that group.

Dalyite, K2ZrSi6O15, occurs in the ejected syenite blocks of Serra de Agua de Pau (Lagoa do Fogo), São Miguel, Azores, in an assemblage sanidine-arfvedsonite-quartz-aegirine-fayalite-astrophyllite-dalyite-pyrrhite. Other blocks from the same locality contain biotite-zircon in place of astrophyllite-dalyite. A comparison made between the chemistry of one specimen of each type indicates that they may be related by paraeutectoid fractional crystallization.

The first iron-rich hypersthene reported was from Vittinki in Finland and was described by M. Saxén in 1925. In 1932 N. Sundius showed that the so-called 'iron-anthophyllite' from Tunaberg in Sweden was really a very iron-rich hypersthene. He suggested that two other 'iron-anthophyllites' occurring similarly in the eulysites of Sweden at Bygdsiljum and at Mansjö might also prove to be really iron-rich hypersthenes.

Here chemical and optical data are given for the Mansjö mineral which fits well into the series and proves to be slightly richer in iron than the Tunaberg one. Data are also given for hypersthenes from Loch Duich and from Glen Buchat in Aberdeenshire, while, thanks to the kindness of Professor P. Eskola, it has been possible to obtain a sample of the Vittinki mineral and to complete the data of M. Saxén.

Barikaite, ideally Pb10Ag3(Sb8As11)Σ19S40, is a new mineral species from the Barika Au-Ag deposit, Azarbaijan Province, western Iran. It was formed in fractures developed in silica bands situated in massive banded pyrite and baryte ores. These fractures house veinlets that contain a number of Ag-As-Sb-Pb-rich sulfosalts, tetrahedrite-tennantite, realgar, pyrite and electrum. Barikaite appears as inclusions in guettardite. The mineral is opaque, greyish black with a metallic lustre; it is brittle without any discernible cleavage. In reflected light barikaite is greyish white, pleochroism is distinct, white to dark grey. Internal reflections are absent. In crossed polars, anisotropism is distinct with rotation tints in shades of grey. The reflectance data (%, in air) are: 37.0, 39.3 at 470 nm, 34.1, 36.9 at 546 nm, 33.1, 36.2 at 589 nm and 31.3, 34.1 at 650 nm. The Mohs hardness is 3–3½, microhardness VHN50 exhibits the range 192 – 212, with a mean value of 200 kg mm–2. The average results of five electron-microprobe analyses in a grain are (in wt.%): Pb 35.77(33), Ag 5.8(1), Tl 0.15(08), Sb 18.33(09), As 15.64(16), S 24.00(15), total 99.69(10) wt.%, corresponding to Pb9.31Ag2.90Tl0.04(Sb8.12As11.26)Σ19.36S40.37 (on the basis of 32Me + 40S = 72 a.p.f.u.). The simplified formula, Pb10Ag3(Sb8As11)Σ19S40, is in accordance with the results of a crystal-structure analysis, and requires Pb 37.89, Ag 5.91, Sb 17.79, As 15.05 and S 23.42 (wt.%). The variation of chemical composition is minor, the empirical formula ranging from Pb10.39Ag2.32Tl0.02Sb7.52As11.27S40.49 to Pb9.24Ag2.93Tl0.04Sb8.13As11.35S40.31. Barikaite has monoclinic symmetry, space group P21/n and unit-cell parameters a 8.5325(7) Å, b 8.0749(7) Å, c 24.828(2) Å, and b 99.077(6)o, Z = 1. Calculated density for the empirical formula is 5.34 (g cm–3). The strongest eight lines in the (calculated) powder-diffraction pattern [d in Å(I)(hkl)] are: 3.835(63)(022), 3.646(100)(016), 3.441(60)(212), 3.408(62)(14), 2.972(66)(16), 2.769(91)(222), 2.752(78)(24) and 2.133(54)(402). Barikaite is the N = 4 member of the sartorite homologous series with a near-equal role of As and Sb, which have an ordered distribution pattern in the structure. It is a close homeotype of rathite and more distantly related to dufrénoysite (both distinct, pure arsenian N = 4 members) and it completes the spectrum of Sb-rich members of the sartorite homologous series. The new mineral and its name have been approved by the IMA-CNMNC (IMA 2012-055).

New microthermometric data are presented for fluid inclusions in epidote, garnet, hedenbergite, armenite, quartz, fluorite, calcite and baryte associated with skarn-related base metal mineralization in the Iglesiente and Sulcis mining districts of SW Sardinia. Based on a comparison of these data with published results for vein and palaeokarst mineralization a ‘two fluid’ model is proposed for the mineralization in the area. An early fluid, responsible for skarn-associated sulphide mineralization, developed above 350–400°C with a salinity generally less than about 10 eq. wt.% NaCl, and on cooling was also responsible for some of the vein and palaeokarst mineralization. The origin of this fluid is, at this stage, speculative (meteoric/magmatic?). A separate fluid regime, characterized by lower temperatures and much higher salinities (Th < 140°C and >20 eq. wt. % NaCl) was mainly responsible for the bulk of the Permo-Triassic vein and palaeokarst mineralization, and some late-stage skarn mineralization. This low-temperature, saline (basinal or evaporitic?) brine appears to have mixed with more dilute groundwaters during this stage of mineralization. The existence of two (or more) mineralizing fluids with different characteristics at the end of Hercynian tectonic/magmatic events appears to be widespread throughout the whole of Europe.

The conclusion of Zaffiro et al. (2019; Constraints on the Equations of State of stiff anisotropic minerals: rutile, and the implications for rutile elastic barometry. Mineralogical Magazine, 83, 339–347) that the Mie–Grüneisen–Debye (MGD) Equation of State (EoS) cannot fit the available data for rutile is shown to be incorrect, even though rutile exhibits significant anisotropic thermal pressure which invalidates the quasi-harmonic approximation used as the basis for the MGD EoS. The refined parameters for the MGD EoS of rutile are: KTR0= 205.05(25) GPa, $K_{TR0}^{\prime} $ = 7.2(5), θD = 399(20) K, γ0= 1.40(2) and q = 1.5(7). This EoS predicts volumes, bulk moduli and volume thermal expansion coefficients for rutile at metamorphic conditions that are statistically indistinguishable from those predicted by the ‘isothermal’ type of EoS reported previously.

New intersectorial isotope data are presented for two calcites. Mendip calcite shows no detectable δ13C and δ18O differences between synchronous {214} and {014} sectors. Nottingham calcite shows a δ13C difference of 1.0‰ and a δ18O difference of 0.5‰ between synchronous {401} and {0001} sectors. Data now available for 5 different calcites show the magnitude of intersectorial fractionation is variable; the effect on δ13C is twice that on δ18O. All five natural calcites also show erratic isotopic differences between symmetrically-equivalent synchronous sectors. Intersectorial isotopic fractionation is probably widespread but its cause and quantification require further work. Synchronous intracrystalline isotopic differences should be accommodated in the interpretation of isotopic data and should influence future sampling strategy.

The temperature (T) and pressure (P) dependence of dielectric and conductivity properties of natural leucite were determined using complex impedance spectroscopy at frequencies from 103 to 106 Hz. Experiments were carried out in a Walker multi-anvil cell at 1 atm and P from 2.5 to 6 GPa and at T from 350 to 800°C. At pressure >6 GPa and temperature >790°C the leucite broke down to kalsilite+sanidine and dielectric properties for this phase assemblage are given at 6.0–7.0 GPa and T to 1050°C.

Leucite conductivity increases with increasing T and decreases with increasing P reflecting their different effects on migration of K cations within the channels in the leucite aluminosilicate framework. Activation energies for K+ migration in leucite increase with increasing pressure (0.74–0.97 eV; 70.0–93.2 kJ/mol) and activation volumes for leucite increase with increasing T (6.42–9.51 cm3/mol; 400–700°C). The latter data provide model K+ cation diameters increasing from 2.7 Å at 400°C to 3.2 Å at 700°C. These values are consistent with the earlier suggestion of Palmer and Salje that the ionic mobility mechanism consists of diffusion along <110> rather than along the main channels parallel to <111>.

The colours of natural and synthetic beryl (ideally Be3Al2Si6O18) have been attributed either tothe presence of chromophore ions partially replacing Al and/or Be (Cr3+, Fe2+/3+, Mn2+) or to the occurrence of colour centres related to the presence of multi-atomic groups. However, no full explanation has been proposed for the blue colour in natural beryl gemstones (aquamarine) despite it being well established that bluish-green synthetic aquamarines containing Fe turn blue when heated for 1 h at 400°C.

A X-ray absorption near-edge spectroscopy (XANES) study at the Fe K-edge was performed on blue beryl crystals from Licungo pegmatite (Mozambique) to ascertain the speciation state of this colouring element, reported in blue sapphire (ideally Al2O3) as a mixture of Fe2+ and Fe3+ in octahedral coordination. The general trend of the spectra is the same when synchrotron radiation (SR) impinges along the c axis of the hexagonal crystal, as well as along the a axis with c vertical. Conversely, a shoulder in the absorption edge is noticed when the incident beam is perpendicular to c, with this axis horizontal in the polarization plane of the SR beam, a reverse in the relative intensities of the two post-edge features is simultaneously observed. Pre-edge features accounting for Fe speciation (valence plus coordination) are identical in all three situations. Considering previous approaches which account for polarization, an explanation is suggested for the special effects observed on the Fe K-edge XANES spectra of analysed blue beryl crystals. Ideas on the origin of the blue colour of this mineral are also presented.

The new alluaudite-group mineral badalovite was found in the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with hematite, tenorite, cassiterite, johillerite, nickenichite, calciojohillerite, bradaczekite, metathénardite, aphthitalite, langbeinite, calciolangbeinite, sanidine, fluorophlogopite, fluoborite, tilasite, anhydrite, pseudobrookite, sylvite, halite, lammerite, urusovite, ericlaxmanite, arsmirandite, svabite, krasheninnikovite, euchlorine, wulffite and alumoklyuchevskite. Badalovite forms oblique-angled prismatic crystals up to 1 mm × 1 mm × 5 mm, typically combined in groups or crusts up to several hundred cm2 in area. The mineral is transparent, green, grey, yellow or colourless, with vitreous lustre. It is brittle, the Mohs hardness is 3½. Cleavage was not observed, the fracture is uneven. Dcalc is 4.02 g cm–3. Badalovite is optically biaxial (–), α = 1.753(3), β = 1.757(3), γ = 1.758(3) and 2Vmeas. = 50(10)°. Chemical composition (wt.%, electron-microprobe; holotype) is: Na2O 9.23, K2O 0.19, CaO 2.04, MgO 13.78, MnO 0.31, CuO 0.12, ZnO 0.24, Al2O3 0.06, Fe2O3 12.77, TiO2 0.01, SiO2 0.06, P2O5 0.33, V2O5 0.05, As2O5 61.51, SO3 0.02, total 100.72. The empirical formula based on 12 O apfu is Na1.67Ca0.20K0.02Mg1.92Zn0.02Mn0.02Cu0.01Fe3+0.90Al0.01(As3.01P0.03Si0.01)Σ3.05O12. The simplified formula is Na2Mg2Fe3+(AsO4)3. Badalovite is monoclinic, C2/c, a = 11.9034(3), b = 12.7832(2), c = 6.66340(16) Å, β = 112.523(3)°, V = 936.59(4) Å3 and Z = 4. The strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 6.41(38)(020), 5.505(20)(200), 3.577(23)($\bar{1}$31), 3.523(25)(310), 3.211(46)($\bar{1}$12), 2.911(28)($\bar{2}$22, $\bar{3}$12), 2.765(100)(240, 400) and 2.618(26)($\bar{1}$32). The crystal structure was solved from single-crystal XRD data with an R1 of = 2.49%. Badalovite is isostructural with other alluaudite-group minerals. Its simplified crystal chemical formula is A(1)NaA(1)’□A(2) □A(2)’NaM(1)MgM(2)(Mg0.5Fe3+0.5)2(AsO4)3 (□ – vacancy) and the end-member formula is NaNaMg(MgFe3+)(AsO4)3. The mineral is named in honour of the outstanding mineralogist and geochemist Stepan Tigranovich Badalov (1919–2014).

The technique of X-ray absorption microspectroscopy is described, with particular reference to the determination of calcium in a hydrogel formed in minute amounts in cavities in larnite. The method, which is applicable to other elements, enables chemical data to be obtained from selected small areas in a normal petrological thin section.

One of the most promising uses of X-ray diffraction methods in mineralogy is the study of those minerals which are opaque and whose crystals are extremely minute. Although recent methods of ore examination by reflected polarized light have given valuable information about these substances, their application to soft, powdery materials is extremely difficult, an objection which does not apply to X-ray methods.

Pyrolusite (including polianite).—The present study had for its main objective an attempt to settle, by X-ray examination , the uncertainty existing as to the relationship between polianite and pyrolusite, Work already carried out by St. Johns has suggested that polianite and pyrolusite are identical, since they have the same cell sides as found from powder photographs.

Two new occurrences of the lead oxy-sulfosalt chovanite have been identified at the Monte Arsiccio and Pollone mines, Apuan Alps, Tuscany, Italy. Chovanite from Monte Arsiccio occurs as black acicular crystals, up to 5 mm long, associated with rouxelite, robinsonite, sphalerite, valentinite,baryte, dolomite, quartz and Ba-rich K-feldspar ('hyalophane') in metadolostone vugs. Its unit-cell parameters are a = 48.38(5), b = 4.11(4), c = 34.18(4) Å, β = 106.26(2)°, V = 6521(64) Å3, space group C2/m. Very weakreflections indicate the doubling of the b parameter. Electron-microprobe data gave (wt.%): Ag 0.28, Tl 1.51, Pb 45.57, Sb 31.00, As 1.09, S 19.73, Se 0.05, Cl 0.02, sum 99.25. On the basis of ∑Me = 58 apfu, its formula is Ag0.30Tl0.86Pb25.56Sb29.59As1.69S71.52Se0.07Cl0.05.Adding one oxygen atom, it is close to the formula TlPb26(Sb,As)31S72O. Chovanite from Pollone occurs as thick black acicular crystals, up to 1 cm long, associated with baryte and quartz. The high-diffraction quality of the available material allowed the solutionand refinement of the 8 Å crystal structure in the space group P21/c, with unit-cell parameters a = 34.052(3), b = 8.2027(7), c = 48.078(4) Å, β = 106.258(4)°, V = 12891.9(19) Å3. The refinement convergedto R1 = 9.14% on the basis of 19,853 observed reflections with Fo > 4σ(Fo). Electron-microprobe data gave (wt.%): Ag 0.12, Tl 0.54, Pb 48.34, Bi 0.20, Sb 26.71, As 3.37, S 20.23, Cl 0.07, sum 99.57. It corresponds to the formulaAg0.13Tl0.30Pb26.94Bi0.10Sb25.33As5.20S72.85Cl0.20, close to the idealized formula Pb28(Sb,As)30S72O, with a single oxygen atom bound to two (Sb/As) atoms alternating witha vacancy along b as in scainiite and in other Pb oxy-sulfosalts. The crystal chemistry of this 8 Å crystal structure is detailed, taking into account its modular description, the (Sb,As)mSn polymerization, its topological derivation from pellouxite,and the oxygen non-stoichiometry.

Fluorine-rich prismatine, (□,Fe,Mg)(Mg,Al,Fe)5Al4(Si,B,Al)5O21(OH,F), with F/(OH+F) = 0.36–0.40 and hercynite are major constituents of a Fe-Al-B-rich lens in ultrahigh-temperature granulite-facies quartz-sillimanite-hypersthene-cordierite gneisses of the Eastern Ghats belt, Andhra Pradesh, India. Hemo-ilmenite, sapphirine, magnetite, biotite and sillimanite are subordinate. Lithium, Be and B are concentrated in prismatine (140 ppm Li, 170 ppm Be, and 2.8 –3.0 wt.% B2O3). Another Fe-rich lens is dominantly magnetite, which encloses fine-grained zincian ferrohögbomite-2N2S, (Fe2+,Mg,Zn,Al)6 (Al,Fe3+,Ti)16O30(OH)2, containing minor Ga2O3 (0.30 –0.92 wt.%). Fe-Al-B-rich lenses with prismatine (or kornerupine) constitute a distinctive type of B-enrichment in granulite-facies rocks and have been reported from four other localities worldwide. A scenario involving a tourmalineenriched lateritic precursor affected by dehydration melting is our preferred explanation for the origin of the Fe-Al-B-rich lenses at the five localities. Whole-rock analyses and field relationships at another of these localities, Bok se Puts, Namaqualand, South Africa, are consistent with this scenario. Under granulite-facies conditions, tourmaline would have broken down to give kornerupine-prismatine (±other borosilicates) plus a sodic melt containing H2O and B. Removal of this melt depleted the rock in Na and B, but the formation of ferromagnesian borosilicate phases in the restite prevented total loss of B.

Krásnoite is a new mineral (IMA2011-040) from the Huber open pit, Krásno ore district, Czech Republic and the Silver Coin mine, Nevada, USA. Krásnoite is the fluorophosphate analogue of perhamite. Krásnoite occurs as compact to finely crystalline aggregates, balls and rosette-like clusters up to 1 mm across. Individual crystals are platy, show a hexagonal outline and can reach 0.1 mm on edge at Krásno and 0.4 mm at Silver Coin. At both localities, krásnoite occurs very late in phosphaterich paragenetic sequences. Krásnoite crystals are partly transparent with a typically pearly lustre, but can also appear greasy (Krásno) or dull (Silver Coin). The streak is white and the hardness is 5 on the Mohs scale. Crystals are brittle, have an irregular fracture, one imperfect cleavage on {001} and are not fluorescent under SW and LW ultraviolet light. Penetration twinning ⊥ {001} is common. The density for both Krásno and Silver Coin material is 2.48(4) g cm–3, measured by the sink–float method in an aqueous solution of sodium polytungstate. The calculated density is 2.476 g cm–3 (Krásno). Krásnoite crystals are uniaxial (+), with ω = 1.548(2) and ε = 1.549(2) (Krásno) and ω = 1.541(1) and ε = 1.543(1) (Silver Coin). The simplified formula of krásnoite is: Ca3Al7.7Si3P4O23.5(OH)12.1F2·8H2O. Krásnoite is trigonal, space group Pm1, with a = 6.9956(4), c = 20.200(2) Å, V = 856.09(9) Å3 and Z = 3. Raman and infrared spectroscopy, coupled with magic-angle spinning nuclear magnetic resonance (MAS–NMR) spectrometry, confirmed the presence of PO3F, PO4, SiO4, H2O and OH in the crystal structure of krásnoite.

Thallium leucite, TlAlSi2O6, has been synthesized at 450°C for 7 days, under ambient conditions, by the transformation of dehydrated analcime NaAlSi2O6 in the presence of excess TlCl. This substitution of Tl for Na leads to confirmation of a thallium-leucite pseudomorph after analcime. Their optical properties, X-ray powder diffraction patterns, electron microprobe analysis, infrared spectra, and X-ray photoelectron spectroscopy have characterized the synthetic Tl-leucites. The IR spectra show that the mid-IR modes T-O stretching and T-O-T bending vibrations for TlAlSi2O6 are more resemblant of those for analcime than for leucite, KAlSi2O6. This resemblance implies that Tl cation enters the W-site rather than the S-site in the analcime structure: Na (S) + H2O (W) ⇋ □ + K (leucite) ⇋ □ + Tl (Tl- leucite), where □ represents an S-site vacancy. The mechanism of this substitution is supported by the crystal chemical constraints: inasmuch as the S-site is smaller than the W-site, Tl+ cations being larger than Na+ plainly prefer the latter site to the former. One inference from the binding energy for Tl+ by XPS is that Tl+ occupies the extra-framework site in synthetic leucite pseudomorph, rather than the smaller tetrahedral site. The difference in Al/Si disordering between analcime and leucite and the nonstoichiometry due to the solid solution of the □Si3O6 component into the leucite structure may provide a fundamental insight into understanding why TlAlSi2O6 deviates from the trend defined by K-, Rb- and CsAlSi2O6 leucite series on the a-c parameter diagram, inasmuch as these three cations in the leucite structure occupy the W-sites. Finally, synthesis of TlAlSi2O6 leucite has an implication for the existence of other polymorphs due to different degrees of Al/Si disordering, except for high- and low-temperature leucites already known: natural leucites crystallized directly through igneous processes are different from those formed by substitution of K for Na in analcimes.