Physics and Chemistry of Minerals最新文献

{"title":"Mechanisms and conditions of Ti and Cr incorporation in mantle phlogopite: the results of atomistic simulation","authors":"Aleksandra A. Bendeliani,&nbsp;Nikolay N. Eremin,&nbsp;Andrey V. Bobrov","doi":"10.1007/s00269-023-01232-x","DOIUrl":"10.1007/s00269-023-01232-x","url":null,"abstract":"<div><p>Modeling of eight mechanisms for the incorporation of Ti⁴⁺ and Cr³⁺ impurity components into phlogopite was carried out by a semi-empirical method using the GULP (General Utility Lattice Program) software. The calculation of thermodynamic mixing properties in the range of 1–7 GPa and 373–1573 K and the analysis of the structure geometry for the simulated solid solutions provided the following energy-preferred schemes of isomorphic substitution: ^VI(Mg²⁺) + 2^IV(Si⁴⁺) = ^VI(Ti⁴⁺) + 2^IV(Al³⁺) and ^VI(Mg²⁺) + 2^IV(Al³⁺) = ^VI(□) + 2^IV(Ti⁴⁺), ^VI(Mg²⁺) + ^IV(Si⁴⁺) = ^VI(Cr³⁺) + ^IV(Al³⁺), and 3^VI(Mg²⁺) = ^VI(Al³⁺) + ^VI(Cr³⁺) + ^VI(□). It is shown the scheme 2^VI(Mg²⁺) = ^VI(Ti⁴⁺) + ^VI(□) illustrating entrance of Ti with the formation of a vacancy is realized in the case of microconcentrations of Ti only. Accumulation of high-Ti contents associates with the formation of a vacancy in the octahedral site. This provides incorporation of Ti via the schemes ^VI(Mg²⁺) + 2^IV(Al³⁺) = ^VI(□) + 2^IV(Ti⁴⁺) and (Mg, Fe²⁺) + 2OH⁻ = Ti⁴⁺  + 2O²⁻ only. It is shown that incorporation of high-Cr concentrations (&gt; 5.5 wt % Cr₂O₃) is accompanied by an increase in the number of vacancies in the octahedral site with an increase in the proportion of the dioctahedral component K(Al, Cr, □)₂AlSi₃O₁₀(OH)₂.</p></div>","PeriodicalId":20132,"journal":{"name":"Physics and Chemistry of Minerals","volume":"50 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-02-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00269-023-01232-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4418265","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Influence of octahedral site chemistry on the elastic properties of biotite","authors":"Dillon F. Hanlon,&nbsp;G. Todd Andrews,&nbsp;Roger A. Mason","doi":"10.1007/s00269-022-01230-5","DOIUrl":"10.1007/s00269-022-01230-5","url":null,"abstract":"<div><p>Brillouin light scattering spectroscopy was used along with detailed composition information obtained from electron probe microanalysis to study the influence of octahedral site chemistry on the elastic properties of natural biotite crystals. Elastic wave velocities for a range of directions in the <i>ac</i> and <i>bc</i> crystallographic planes were obtained for each crystal by application of the well-known Brillouin equation with refractive indices and phonon frequencies obtained from the Becke line test and spectral peak positions, respectively. In general, these velocities increase with decreasing iron content, approaching those of muscovite at low iron concentrations. Twelve of thirteen elastic constants for the full monoclinic symmetry were obtained for each crystal by fitting analytic expressions for the velocities as functions of propagation direction and elastic constants to corresponding experimental data, while the remaining constant was estimated under the approximation of hexagonal symmetry. Elastic constants <span>(C_{11})</span>, <span>(C_{22})</span>, and <span>(C_{66})</span> are comparable to those of muscovite and show little change with iron concentration due to the strong bonding within layers. In contrast, nearly all of the remaining constants show a pronounced dependence on iron content, a probable consequence of the weak interlayer bonding. Similar behaviour is displayed by the elastic stability, which exhibits a dramatic decrease with increasing iron content, and by the elastic anisotropy within the basal cleavage plane, which decreases as the amount of iron in the crystal is reduced. This systematic dependence on iron content of all measured elastic properties indicates that the elasticity of biotite is a function of octahedral site chemistry and provides a means to estimate the elastic constants and relative elastic stability of most natural biotite compositions if the iron or, equivalently, magnesium, concentration is known. Moreover, the good agreement between the elastic constants of Fe-poor (Mg-rich) biotite and those of phlogopite obtained from <i>first-principles</i> calculation based on density functional theory indicates that the latter approach may be of use in predicting the elastic properties of biotites.</p></div>","PeriodicalId":20132,"journal":{"name":"Physics and Chemistry of Minerals","volume":"50 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4205902","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Single-crystal X-ray diffraction and IR-spectroscopy studies of potassium-deficient fluorapophyllite-(K)","authors":"Yurii V. Seryotkin,&nbsp;Igor N. Kupriyanov,&nbsp;Mark A. Ignatov","doi":"10.1007/s00269-022-01229-y","DOIUrl":"10.1007/s00269-022-01229-y","url":null,"abstract":"<div><p>Three samples of fluorapophyllite-(K) with different cation composition were studied by the X-ray diffraction and IR-spectroscopy methods. The samples (K_0.72(NH₄)_0.20)_Σ0.92Na_0.08 Ca₄[Al_0.04Si_7.96O₂₀]F·8H₂O from Nidym and K_0.87Na_0.06 Ca₄[Si₈O₂₀]F·8H₂O from Akhaltsykhe localities are characterized by the deficiency of large cations K⁺ and (NH₄)⁺ in the A site; the chemical composition of Talnakh sample (K_0.94(NH₄)_0.06)_Σ1.00 Ca₄[Si₈O₂₀]F·8H₂O is close to the stoichiometric one. The large cations deficiency in the structure of Nidym and Akhaltsykhe samples is compensated by the presence of medium-sized Na⁺ cations, located 1.12–1.31 Å away from the A position. The planar coordination of Na is formed by four H₂O molecules. The occurrence of ammonium ions is found for the Nidym and Talnakh samples and their concentrations are estimated from the IR spectra and structure refinement. Polarized infrared measurements performed for fluorapophyllite-(K) samples oriented along the <i>c</i>-axis reveal pleochroic behavior of the OH absorption bands. The observed pleochroism is explained in terms of absorption from two OH vectors of the H₂O molecules in the crystal structure.</p></div>","PeriodicalId":20132,"journal":{"name":"Physics and Chemistry of Minerals","volume":"50 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4208168","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Structural variations of amorphous magnesium carbonate during nucleation, crystallization, and decomposition of nesquehonite MgCO3·3H2O","authors":"Gen-ichiro Yamamoto,&nbsp;Atsushi Kyono,&nbsp;Satoru Okada","doi":"10.1007/s00269-022-01231-4","DOIUrl":"10.1007/s00269-022-01231-4","url":null,"abstract":"<div><p>Carbonate minerals are major contributors to carbon sequestration in geological deposits; however, their nature and behavior remain unclear. Amorphous magnesium carbonate (AMC) is formed as a precursor to crystalline magnesium carbonates and as a product of thermal decomposition of nesquehonite (NSQ). In this study, the AMCs formed during the crystallization and decomposition of NSQ were investigated using X-ray diffraction (XRD) and atomic pair distribution function (PDF) methods. An AMC with a hydromagnesite-like structure (AMC-I) was formed immediately after mixing MgCl₂ and Na₂CO₃ solutions. After 5 min of stirring, no change was observed in the XRD pattern; however, the PDF pattern changed. This suggests that the medium-range ordered structure of AMC-I transformed into an intermediate structure (AMC-II) between AMC-I and NSQ. After 10 min of stirring, the AMC-II crystallized into NSQ. In the case of Rb₂CO₃, the AMC-II structure was formed immediately after the mixing of solutions and was stable for three days. AMC-II in the Rb₂CO₃ solution appeared to be in equilibrium with energetic local minima, indicating the existence of polyamorphism in AMC. When Cs₂CO₃ solution was used, the first precipitate had an AMC-I structure. By stirring for 5 min, the AMC-I was transformed to AMC-II, and after 10 min of stirring, a few quantities crystallized into NSQ. After three days, NSQ dissolved and transformed back into AMC-I. Thus, it is inferred that the crystallization of NSQ is significantly influenced by alkali cations in aqueous solutions. The AMC formed during the thermal decomposition also possesses the AMC-I structure.</p></div>","PeriodicalId":20132,"journal":{"name":"Physics and Chemistry of Minerals","volume":"50 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"5145461","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pressure-induced phase transition of CO32−-bearing scapolite by in situ X-ray diffraction and vibrational spectroscopy","authors":"Cheng Qian,&nbsp;Yungui Liu,&nbsp;Xiang Li,&nbsp;Yudong Zhu,&nbsp;Haipeng Song,&nbsp;Xiang Wu","doi":"10.1007/s00269-022-01226-1","DOIUrl":"10.1007/s00269-022-01226-1","url":null,"abstract":"<div><p>Scapolite Na_2.25Ca_1.43K_0.30Fe_0.02[Al_4.23Si_7.77O₂₄]Cl_0.72(SO₄)_0.1(CO₃)_0.18 has been investigated by single-crystal X-ray diffraction, Infrared and Raman spectroscopy combined with diamond anvil cells (DAC) up to 19.6 GPa at room temperature, to understand its phase stability and the behaviors of CO₃²⁻. The experimental results show that a phase transition from the tetragonal phase (<i>P</i>4₂/<i>n</i>) to the triclinic phase occurs at 10.7 GPa, which is attributed to the pressure-induced rotation of tetrahedra around the bridging O atoms. The pressure–volume data were fitted to the second-order Birch–Murnaghan equation of state, yielding <i>V</i>₀ = 1102.6(8) ų and <i>K</i>₀ = 70.3(9) GPa for the tetragonal phase and <i>V</i>₀ = 1188.2(16) ų and <i>K</i>₀ = 33.0(3) GPa for the triclinic phase. In the triclinic phase, the larger compressibility is due to the increased degree of freedom in the crystal structure, and the anisotropy of the axial compressibility may be related to the ionic radius of the anionic group. From the Infrared absorption and Raman spectroscopy data, we speculate that CO₃²⁻ is extruded by the four-membered rings at the (001) plane during the whole pressure range. The high-pressure behavior of CO₃²⁻ in scapolite provides a possibility that carbon exists in the Earth’s interior as CO₃²⁻ coupled to silicates.</p></div>","PeriodicalId":20132,"journal":{"name":"Physics and Chemistry of Minerals","volume":"50 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4643920","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Features of the defect-impurity composition of diamonds from the northern Istok and Mayat placers (Yakutia) according to EPR, IR, and luminescence data","authors":"V. A. Nadolinny,&nbsp;O. P. Yurjeva,&nbsp;M. I. Rakhmanova,&nbsp;A. Yu. Komarovskikh,&nbsp;V. S. Shatsky","doi":"10.1007/s00269-022-01227-0","DOIUrl":"10.1007/s00269-022-01227-0","url":null,"abstract":"<div><p>Diamonds from placers in the northern provinces of the Siberian Platform attract attention not only due to the unsolved problem of their sources but also due to the variety of properties they exhibit. In this work, electron paramagnetic resonance (EPR), infrared (IR), and photoluminescence (PL) methods were used to study cuboid diamonds from Istok (25 diamonds of Ib-IaA type) and dodecahedron diamonds from Mayat (21 diamonds of IaAB type) placers. The main impurity defects in the crystals studied are nitrogen, nitrogen-titanium, and oxygen-containing centers. The total amount of nitrogen in the form of C (P1 in EPR nomenclature), A, and B centers ranges from 34 to 903 ppm. For 19 out of 25 crystals from the Istok placer, the N3 titanium-related center is observed in the EPR spectra, but only one optical system with zero-phonon line (ZPL) at 635.7 nm is detected in the PL spectra in most cases. It can be assumed that the absence of an accompanying system with ZPL at 440.3 nm is due to its quenching by other centers in these crystals. For 12 out of 21 crystals from the Mayat placer, photoluminescence of oxygen-containing centers in the region of 600–800 nm in the form of a series of equidistant bands with an interval of ~ 31 meV was revealed. A comparison of the EPR and PL data has shown that this red broad band is not correlated with titanium-nitrogen paramagnetic centers OK1 and N3. Thus, the results obtained for diamond crystals from the Istok and Mayat placers show no connection between the N3 and OK1 paramagnetic centers and band in the 600–800 nm region, which questions the presence of oxygen in the structure of the N3 and OK1 centers. The nickel-nitrogen centers were found in crystals from the Mayat placer testifying about the peridotitic paragenesis of these diamonds.</p></div>","PeriodicalId":20132,"journal":{"name":"Physics and Chemistry of Minerals","volume":"50 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4639739","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spectral variability of the uranyl silicates uranophane-α and uranophane-β: polymorphism and luminescence","authors":"Martin Stark,&nbsp;Markus Noller","doi":"10.1007/s00269-022-01225-2","DOIUrl":"10.1007/s00269-022-01225-2","url":null,"abstract":"<div><p>The luminescence of the uranyl cation UO₂²⁺ depends on the local crystalline environment and is sensitive to structural influences. Steady-state photoluminescence emission spectra of the related uranyl silicates uranophane-α, uranophane-β, sklodowskite and haiweeite from various locations are presented and discussed in the light of structure–property relation. The four mineral species were chosen for their close relationships: uranophane-α and uranophane-β are polymorphs and share the underlaying topology with sklodowskite. Haiweeite, with different topology, shares the composing elements Ca, U, Si, O with uranophane, while in sklodowskite Mg replaces Ca. All species show some variability in their spectra, parameterized as a variation of the centroid wavelength. Those variations are linked to defects and structural disorder, relevant in studies of uranyl speciation and migration. We present empiric spectra of the four mineral species with the least influence of structural disorder. As an unexpected feature, a prominent—partly dominating—double peak structure occurs in the case of uranophane-α only, while it is absent in the spectra of the other species. Considering a model of luminescent transitions in the uranyl ion in more detail, this observation is discussed in the light of the polymorphism of uranophane. We show evidence that variable amounts of uranophane-β phase embedded in uranophane-α are possibly at the origin of this spectral signature. Growth of those uranophane-β clusters might be induced by defects in the uranophane-α lattice and further promoted by the polymorphism of uranophane.</p></div>","PeriodicalId":20132,"journal":{"name":"Physics and Chemistry of Minerals","volume":"50 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00269-022-01225-2.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4073363","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Compressibilities along the magnetite–magnesioferrite solid solution","authors":"C. Melai,&nbsp;T. Boffa Ballaran,&nbsp;L. Uenver-Thiele,&nbsp;A. Kurnosov,&nbsp;A. I. Chumakov,&nbsp;D. Bessas,&nbsp;D. J. Frost","doi":"10.1007/s00269-022-01217-2","DOIUrl":"10.1007/s00269-022-01217-2","url":null,"abstract":"<div><p>To calculate the thermodynamic properties of recently discovered high-pressure mixed valence iron oxides in the system Fe–Mg–O, information on the equation of state of precursor inverse spinel phases along the magnetite–magnesioferrite join is needed. The existing equation of state data, particularly for magnesioferrite, are in poor agreement and no data exist for intermediate compositions. In this study, the compressibility of nearly pure magnesioferrite as well as of an intermediate <span>({{mathrm{Mg}}_{0.5}}^{vphantom{2+}}mathrm{Fe}_{0.5}^{2+}{mathrm{Fe}}_{2}^{3+}{mathrm{O}}_{4}^{vphantom{2+}})</span> sample have been investigated for the first time up to approximately 19 and 13 GPa, respectively, using single-crystal X-ray diffraction in a diamond anvil cell. Samples were produced in high-pressure synthesis experiments to promote a high level of cation ordering, with the obtained inversion parameters larger than 0.83. The room pressure unit cell volumes, <i>V</i>₀, and bulk moduli, <i>K</i>_<i>T</i>0, could be adequately constrained using a second-order Birch–Murnaghan equation of state, which yields <i>V</i>₀ = 588.97 (8) ų and <i>K</i>_<i>T</i>0 = 178.4 (5) GPa for magnesioferrite and <i>V</i>₀ = 590.21 (5) ų and <i>K</i>_<i>T</i>0 = 188.0 (6) GPa for the intermediate composition. As magnetite has <i>K</i>_<i>T</i>0 = 180 (1) GPa (Gatta et al. in Phys Chem Min 34:627–635, 2007. https://doi.org/10.1007/s00269-007-0177-3), this means the variation in <i>K</i>_<i>T</i>0 across the magnetite–magnesioferrite solid solution is significantly non-linear, in contrast to several other Fe–Mg spinels. The larger incompressibility of the intermediate composition compared to the two end-members may be a peculiarity of the magnetite–magnesioferrite solid solution caused by an interruption of Fe²⁺–Fe³⁺ electron hopping by Mg cations substituting in the octahedral site.</p></div>","PeriodicalId":20132,"journal":{"name":"Physics and Chemistry of Minerals","volume":"50 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00269-022-01217-2.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4378139","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Correction: Overview of HPCAT and capabilities for studying minerals and various other materials at high-pressure conditions","authors":"Arunkumar Bommannavar,&nbsp;Paul Chow,&nbsp;Rich Ferry,&nbsp;Rostislav Hrubiak,&nbsp;Freda Humble,&nbsp;Curtis Kenney-Benson,&nbsp;Mingda Lv,&nbsp;Yue Meng,&nbsp;Changyong Park,&nbsp;Dmitry Popov,&nbsp;Eric Rod,&nbsp;Maddury Somayazulu,&nbsp;Guoyin Shen,&nbsp;Dean Smith,&nbsp;Jesse Smith,&nbsp;Yuming Xiao,&nbsp;Nenad Velisavljevic","doi":"10.1007/s00269-022-01218-1","DOIUrl":"10.1007/s00269-022-01218-1","url":null,"abstract":"","PeriodicalId":20132,"journal":{"name":"Physics and Chemistry of Minerals","volume":"49 12","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00269-022-01218-1.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"4912972","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Oxidation processes and thermal stability of actinolite","authors":"Constanze Rösche,&nbsp;Naemi Waeselmann,&nbsp;Nadia Petrova,&nbsp;Thomas Malcherek,&nbsp;Jochen Schlüter,&nbsp;Boriana Mihailova","doi":"10.1007/s00269-022-01223-4","DOIUrl":"10.1007/s00269-022-01223-4","url":null,"abstract":"<div><p>Understanding the thermal behaviour of iron-containing amphiboles (AB₂C₅T₈O₂₂W₂, C₅ = <i>M</i>(1)₂<i> M</i>(2)₂<i> M</i>(3)) at atomic-level scale may have important implications in several fields, including metamorphic petrology, geophysics, and environmental sciences. Here, the thermally induced oxidation and decomposition of actinolite are studied by in situ high-temperature Raman spectroscopy and complementary thermogravimetric/mass-spectrometry analyses as well as X-ray diffraction of the products of amphibole decomposition. The effect of ^CFe²⁺ on dehydrogenation/dehydroxylation is followed by comparing the results on actinolite with those for tremolite. We show that mobile charge carriers, namely polarons (conduction electrons coupled to FeO₆ phonons) and H⁺ cations, exist in actinolite at elevated temperatures ~ 1150–1250 K. The temperature-induced actinolite breakdown is a multistep process, involving (i) delocalization of <i>e</i>⁻ from ^CFe²⁺ as well as of H⁺ from hydroxyl groups shared by Fe-containing <i>M</i>(1)<i>M</i>(1)<i>M</i>(3) species, which, however, remain in the crystal bulk; (ii) dehydrogenation and ejection of <i>e</i>⁻ between 1250 and 1350 K, where actinolite can be considered as “oxo-actinolite”, as H⁺ also from hydroxyl groups next to ^{<i>M</i>(1,3)}(MgMgMg) configurations become delocalized and mostly remain in the crystal bulk; (iii) complete dehydroxylation and consequent structure collapse above 1350 K, forming an Fe³⁺-bearing defect-rich augitic pyroxene. The dehydrogenation of tremolite occurs at 1400 K, triggering immediately a disintegration of the silicate double-chain into single SiO₄-chains and followed by a rearrangement of the amphibole octahedral strips and ^BCa²⁺ cations into pyroxene-type octahedral sheets at 1450 K. The result of tremolite decomposition is also a single-phase defect-rich clinopyroxene with an intermediate composition on the diopside–clinoenstatite join.</p></div>","PeriodicalId":20132,"journal":{"name":"Physics and Chemistry of Minerals","volume":"49 12","pages":""},"PeriodicalIF":1.4,"publicationDate":"2022-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00269-022-01223-4.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"5174064","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}