The determination of the cummingtonite content of synthetic tremolite

Gottschalk, Matthias; Andrut, M.; Melzer, Stefan

doi:10.1127/ejm/11/6/0967

Cited by 44 publications

(22 citation statements)

References 14 publications

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“…Synthetic tremolite is known to form with about 3-7 mol% Mg, or 0.06-0.14 atoms per formula unit (apfu), appearing to replace Ca in the M4 site and shifting it slightly from its ideal composition Ca 2 Mg 5 Si 8 O 22 (OH) 2 (e.g., Jenkins 1987;Graham et al 1989;Maresch et al 1994;Zimmerman et al 1996;Gottschalk et al 1999;Bozhilov et al 2004). The great level of interest that this relatively minor deviation from ideal composition has generated stems from the far-reaching implications that it has on such things as: (1) the role that chain multiplicity faults (CMFs) vs. solid solution plays in controlling the bulk mineral composition (Ahn et al 1991;Maresch et al 1994); (2) the effect that confi gurational entropy, arising from cation disorder, can have on stabilizing non-ideal mineral compositions (Hawthorne 1995);…”

Section: Introductionmentioning

confidence: 99%

Biopyribole evolution during tremolite synthesis from dolomite and quartz in CO2-H2O fluid

Bozhilov

Brownstein

Jenkins

2007

American Mineralogist

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the present study deals with the formation of tremolite from dolomite + quartz in a CO 2 -H 2 O fl uid; this has greater relevance to nature. EXPERIMENTAL METHODS Starting materials and sample treatmentNatural white dolomite (northwest Adirondacks, New York) and quartz (locality unknown) were used in this study. Microprobe analysis (procedure described below) of the dolomite indicated that it was unzoned and had a uniform composition of Ca 1.024(7) Mg 0.975(7) Fe 0.001(1) (CO 3 ) 2 , where the number in parenthesis is the uncertainty in the last digit. Dolomite and quartz were ground (but unsized) and mixed in the weight proportions of dolomite to quartz of 65.7 to 34.3 wt%, respectively, ABSTRACT A series of experiments with and without sample retreatment was performed on a starting mixture of dolomite plus quartz at 0.5 GPa and 600 °C in a CO 2 -H 2 O fl uid with a mole fraction of CO 2 of 0.2 for durations up to 582 h. The initial reaction of dolomite and quartz led to rapid formation of talc and calcite instead of tremolite and calcite by the intended reaction: 5 dolomite + 8 quartz + H 2 O = tremolite + 3 calcite + 7 CO 2 . With continued treatment, the talc + calcite + quartz assemblage gradually reacts to form increasing amounts of tremolite and diopside with the eventual loss of quartz and nearly complete loss of talc.The detailed structure of the amphibole and the nature of the Mg enrichment were revealed using AEM analysis of individual amphibole crystals. The most abundant defects are triple-chain chain multiplicity faults (CMFs), which appear as isolated lamellae with single periodicity in short-duration experiments and increasingly as groups of lamellae with variable multiplicity and periodicity in longer duration experiments and especially in a long-duration experiment without retreatment. In this latter experiment, a calcian clinojimthompsonite domain extending 15 unit cells along the b axis was observed. The sample after 582 h and fi ve retreatments shows, on average, 3.5% true solid solution with Mg expressed as the Mg-cummingtonite (MC) component after correction for the presence of CMFs. This sample is thought to most closely approach the equilibrium composition for the amphibole. The sample after 250 h with three retreatments has about 10%, whereas that after 582 h without retreatment has 0.6% MC component, the latter having a relatively high density of CMFs. This study affi rms the importance that precursor non-amphibole biopyriboles play in the formation of tremolitic amphibole.

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Section: Introductionmentioning

confidence: 99%

Biopyribole evolution during tremolite synthesis from dolomite and quartz in CO2-H2O fluid

Bozhilov

Brownstein

Jenkins

2007

American Mineralogist

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“…This substitution is detected in the OH spectrum, which may help in quantifying the actual composition at the B-site in tremolite (Gottschalk et al, 1999 Amphiboles along the join tremolite -potassium-richterite show both bands at 3674 and 3735 cm -1 , the intensities of which are correlated to the amount of tremolite in solid-solution within richterite (and vice-versa) . Notably, the FWHM (full width at half maximum) of the tremolite peak increases for intermediate compositions along the join, because of increasing structural disorder due to the distribution of different cations at the available structural sites.…”

Section: Ftir Spectroscopy Of the Studied Fibresmentioning

confidence: 91%

“…The band assignment for amphiboles in the richterite-tremolite compositional join is well known from the works of Robert et al (1989), Della Ventura et al (1997, Hawthorne et al (1996Hawthorne et al ( , 1997, Gottschalk et al (1999) Gottschalk et al (1999) synthetic tremolite systematically contains a small amount of cummingtonite component in solid-solution, thus its B-site composition is never equal to Ca 2 , but it departs toward Ca 2-x Mg x , with x generally in the range 0.1 to 0.3 apfu. This substitution is detected in the OH spectrum, which may help in quantifying the actual composition at the B-site in tremolite (Gottschalk et al, 1999 Amphiboles along the join tremolite -potassium-richterite show both bands at 3674 and 3735 cm -1 , the intensities of which are correlated to the amount of tremolite in solid-solution within richterite (and vice-versa) .…”

Section: Ftir Spectroscopy Of the Studied Fibresmentioning

confidence: 99%

Asbestiform tremolite within the Holocene late pyroclastic deposits of Colli Albani volcano (Latium, Italy): occurrence and crystal chemistry

Ventura

Caprilli

Bellatreccia

et al. 2014

Rend. Fis. Acc. Lincei

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This work relates the occurrence and the characterization of fibrous tremolite within the latest pyroclastic deposits of the Colli Albani (Alban Hills) volcano, to the south-east of Rome (Italy). These mineralizations were observed during a systematic rock-sampling undertaken to complete the geological survey for the new 1:50 000 map of this volcanic area. The examined specimens were collected inside distal deposits correlated to the last Albano Maar activity, which are geographically located within the boundaries of the Nemi community. Tremolite occurs within both carbonate ejecta and G. Della Ventura (☺) Dipartimento di Scienze, Università di Roma Tre, Largo S. Leonardo Murialdo 1, I-00146 ROMA e-mail: giancarlo.dellaventura@uniroma3.it 2 the host pyroclastic rocks. It shows up as whitish to light gray coloured aggregates of crystals with fibrous aspect and sericeous brightness. Due to the extremely small crystal dimensions, never exceeding 0.5 µm in diameter, the micro-chemical composition of the fibres could be obtained only by combining P-XRD, SEM-EDX and FTIR methods.Infrared spectroscopy, in particular, proved to be a valuable technique to characterize the studied amphibole. The composition determined is that of a Fe-free F-rich (c. 53%) tremolite with significant (c. 20%) richterite components in solid-solution. The occurrence of fibrous tremolite in an inhabited place, occurring as natural geological material rather than being due to anthropogenic pollution, should be examined with concern, because it implies complex health and legal responsibilities in the case of mobilization due to extreme climatic events.

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“…In amphiboles of the tremolite-fluorotremolite series, there is a single (OH)-stretching band at 3674 cm -1 , Gottschalk et al 1999. The position of this band does not change signifi cantly with decreasing F content of the amphibole, but the band intensity decreases monotonically with decreasing F content (Fig.…”

Section: One-mode and Two-mode Behaviormentioning

confidence: 98%

Short-Range Order in Minerals: Amphiboles

Hawthorne¹,

Ventura²,

Oberti³

et al. 2005

The Canadian Mineralogist

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Short-range order involves local clusters of atoms that occur either more or less frequently than predicted by a random distribution. Infrared spectroscopy in the principal (OH)-stretching region is sensitive to such local arrangements, and hence the (OH) group can be used as a local probe of short-range arrangements of atoms. Examination of natural amphiboles of fairly simple composition indicates that the principal (OH)-stretching frequency is sensitive to such local arrangements, generating fi ne structure that gives information on short-range arrangements. Moreover, the fi ne structure is sensitive to both nearest-neighbor and next-nearest-neighbor arrangements. The short-range arrangements that can occur are constrained by the local version of the valence-matching principle, and this helps in assignment of the bands in the fi ne structure of the corresponding infrared spectra. Recent results on synthetic amphiboles illustrate these issues. Monoclinic amphiboles in the systems richterite-pargasite, tremolite-pargasite and tremolite-hornblende show strong SRO involving T-, C-and A-group cations. Amphiboles involving (OH)-F solid-solution with Ⅺ (vacancy) at the A site (e.g., tremolite-fl uorotremolite) show one-mode behavior, whereas amphiboles with Na or K at the A site (e.g., richterite-fl uororichterite) show two-mode behavior, indicating that nearest-neighbor arrangements of atoms couple through an occupied A site, but do not couple through a vacant A site. Furthermore, the relative band intensities in (OH)-F amphibole solid-solutions showing two-mode behavior indicate that (OH) and F are completely short-range disordered with respect to each other in the amphibole series examined thus far. Amphiboles in the system pargasite-fl uoropargasite show strong SRO of (OH) and F with regard to the cations occupying the associated nearest-neighbor M(1)M(1)M(3) sites: arrangements involving MgMgAl-(OH) are far more common than arrangements involving MgMgAl-F. Examination of Ti-bearing richteritic amphiboles show that [4] Ti 4+ and Si are short-range disordered with regard to each other. Crystal-structure refi nement, SIMS analysis and local bond-valence requirements suggest that [6] Ti 4+ and O(3) O 2-are locally associated at adjacent M(1) and O(3) sites in (at least some) amphiboles. It is apparent that SRO is very common in monoclinic amphiboles. Although much work remains to be done to fully characterize SRO in amphiboles, the general features are already emerging, and local bond-valence requirements seem to be the (principal) factor controlling this type of order. SRO is of signifi cance in that it will affect the stability of amphiboles (and other minerals in which it occurs) through its entropy (and enthalpy) effects; the way in which these effects can be formulated for such a complicated case is not yet clear, but what is clear is that future thermodynamic models need to consider SRO in amphiboles and probably in other minerals in which heterovalent substitutions are common.Keywords: short-rang...

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The determination of the cummingtonite content of synthetic tremolite

Cited by 44 publications

References 14 publications

Biopyribole evolution during tremolite synthesis from dolomite and quartz in CO2-H2O fluid

Biopyribole evolution during tremolite synthesis from dolomite and quartz in CO2-H2O fluid

Asbestiform tremolite within the Holocene late pyroclastic deposits of Colli Albani volcano (Latium, Italy): occurrence and crystal chemistry

Short-Range Order in Minerals: Amphiboles

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