Very unusual rocks consisting of natrolite (>95 vol.%) ± pargasite (<5 vol.%) and rarealbite (<1 vol. %) have been discovered in the Kop mountain range, eastern Turkey. We propose to call these rocks ‘natrolitite’ and ‘pargasite natrolitite’. They were produced by Na Si metasomatism of dikes and stocks of diorite through replacement of the intermediate primary igneous plagioclase to produce natrolite. The metasomatic alteration produced concentric elliptical zones characterized by distinct mineral assemblages centered on intrusions of diorite. The Central Zone 1 consists of variably albitized diorite with preserved magmatic textures (albite ± andesine ± pargasite ± quartz). Transition Zone 2 comprises natrolite-bearing diorite (natrolite ± albite ± andesine ± pargasite ± calcite ± quartz). Marginal Zone 3 is a rock made up almost entirely of natrolite (natrolite ± pargasite ± albite ± calcite ± chlorite). Outer Zone 4 occurs along the boundary between the natrolitite and the surrounding serpentinite and consists of listvenite, a rock which comprises magnesite, quartz, calcite, mica, talc, and hematite, indicating a role for CO2 in the metasomatic reactions, consistent with the presence of calcite in the alteration zones. Zone 5 consists essentially of brecciated serpentinite with numerous hydrothermal quartz veins and calcite veins. Whole-rock compositions document an increase in Na2O, Al2O3, and H2O from the core (central zone) to themargin while CaO, MgO, and SiO2 decrease. Plagioclase abundance and composition also varies outwards from the central core rocks where it occurs as a primary magmatic phase (∼95 vol.% An41−38) to the alteration zones (<5 vol.% An32−37) due to partial to complete replacement of plagioclase by natrolite with or without rare albite. The natrolites exhibit little variation in Si/Al ratios, ranging between 1.45 and 1.61, and are similar in composition to those reported in the literature. Accompanying pargasitic amphibole also becomes progressively more sodic in composition from the core rocks to the marginal zone rocks. Our analysis indicates that albitization preceded the formation of natrolite and that the formation of natrolite, instead of other more typical alteration minerals (e.g. analcime and paragonite), reflects Na metasomatism at lower chemical potentials for Al2O3 and SiO2. Potential sources of Na could be hypersaline brines or leaching of country rocks, such as trondhjemites. The fluids were driven in hydrothermal convection cells set up by theintrusion of thediorites.

A calorimetric method for determining isothermal partial and integral heats of hydration reactions ($\text{Δ}{\overline{H}}_{\text{R,}T,P}$${\rm{\Delta }}{\bar H_{{\rm{R,}}T,\,P}}$ and $\text{Δ}{\stackrel{\sim }{H}}_{\text{R,}T,P}$${\rm{\Delta }}{\tilde H_{{\rm{R,}}T,\,P}}$, respectively) in zeolites and other mineral hydrates is presented. The method involves immersing a dehydrated sample in a humid gas stream under isothermal conditions within a thermal analysis device that records simultaneous differential scanning calorimetric (DSC) and thermogravimetric analysis (TGA) signals. Monitoring changes in sample mass (corresponding to extent of reaction progress) coincident with a quantitative measurement of heat flow allows for direct detection of $\text{Δ}{\overline{H}}_{\text{R,}T,P}$${\rm{\Delta }}{\bar H_{{\rm{R,}}T,\,P}}$ as a function of the extent of hydration, which can be integrated to determine $\text{Δ}{\stackrel{\sim }{H}}_{\text{R,}T,P}$${\rm{\Delta }}{\tilde H_{{\rm{R,}}T,\,P}}$. In addition, it eliminates uncertainties associated with imprecise knowledge of the starting and final states of a sample during hydration. Measurement under isothermal conditions removes uncertainties associated with heat capacity effects that complicate interpretations of DSC measurements of dehydration heats conducted under traditional scanning temperature conditions. Example experiments on the zeolites natrolite, analcime and chabazite are used to illustrate strategies for quantifying $\text{Δ}{\overline{H}}_{\text{R,}T,P}$${\rm{\Delta }}{\bar H_{{\rm{R,}}T,\,P}}$ and $\text{Δ}{\stackrel{\sim }{H}}_{\text{R,}T,P}$${\rm{\Delta }}{\tilde H_{{\rm{R,}}T,\,P}}$ and minimizing errors associated with baseline uncertainties. Results from this method agree well with previously published values determined by other calorimetric techniques and regression of phase equilibrium data. In the case of chabazite, the results allowed detailed measurements of the variation in $\text{Δ}{\overline{H}}_{\text{R,}T,P}$${\rm{\Delta }}{\bar H_{{\rm{R,}}T,\,P}}$ for energetically different water types encountered progressively as the sample absorbed water. This technique complements and in many cases improves the quality of thermodynamic data obtained through phase equilibrium observations and other calorimetric techniques.

A natrolite-cemented palagonite ash tuff unit is reported in a palaeo-basin in northeast Jordan. Phillipsite and chabazite are also identified. The zeolites were formed due to transformation of volcanic glass granules into palagonite by the reaction with percolating water in a closed hydrological system. Consequently, Si, Al, Ca, Na and K are leached out and precipitated in a series of authigenic layers developed at the extreme edge of the granules. The recorded paragenetic sequence is smectite → phillipsite → chabazite → natrolite → analcime → calcite. The natrolite studied is chemically similar to those reported in the literature with minor variations. The phillipsite and chabazite studied are chemically different from the other Jordanian phillipsite and chabazite reported. The latter are chemically equivalent to those formed under open hydrological systems, whereas the phillipsite and chabazite in this study are chemically equivalent to those formed in saline lakes and arid soil environments. This conclusion is based on the (Na+K)/(Na+K+Ca+Mg) ratio and the Si/Al ratio.

Selected samples of large cavity filling and vein-type fibrous zeolites from Eocene volcanic rocks in the Kahrizak region, northern Iran, have been studied for their mineralogical and chemical characteristics. X-ray powder diffraction and electron microprobe analyses confirmed the presence of natrolite, mesolite and scolecite with compositions of [Na14.922Ca0.202K0.015Ba0.002] [Al15.697Si24.267O80]·nH2O, [Ca15.714Na14.224][Al46.431Si73.398O240]·nH2O and [Ca7.804Na0.142K0.024 Ba0.012Mg0.006][Al15.320Si24.437O80]·nH2O, respectively. In addition, examination of textural relationships in thin sections and back-scattered electron images reveals a paragenetic order in which the Ca-rich zeolites crystallized first. It is most probable that the fibrous zeolites of Kahrizak were formed during two pulses of hydrothermal activity in the area. Scolecite and mesolite were precipitated from Ca-rich solution, whereas the second stage Na-rich, low-temperature fluid crystallized natrolite and reacted with Ca-species.

This paper presents a literature survey of compositions of the fibrous zeolites mesolite, natrolite, thomsonite and their derivatives such as pseudomesolite, high-Na mesolite, tetranatrolite, paranatrolite, ranite, and gonnardite, and evaluates them in the light of new electron probe analyses and X-ray powder data for gonnardites and associated minerals from Aci Castello, Gignat, Hills Port, Kladno, and Lamo. The analyses are plotted on the basis of bivalent vs. trivalent cations per 80 oxygen cell and a new chemical classification is tentatively proposed. It is concluded that ranite is definitely not synonymous with gonnardite and until species status is confirmed it is useful to retain this term as a Ca- and Al-rich disordered variety of natrolite. It is further concluded that natrolite and tetranatrolite contain up to 2 Ca, ranite 2–4 Ca, gonnardite 4–6 Ca and thomsonite 6–8 Ca atoms with corresponding limits on the Al atoms. Compositions are governed by NaSi = CaAl and to some extent by Na2 = Ca type replacements and the Al-content generally varies sympathetically with Ca-content. The plot reveals that most high-Na mesolites are ranites, a number of gonnardites are ranites and one or two are tetranatrolites. The compositional field of gonnardite crosses that of mesolite (and pseudomesolite), but these minerals can be easily distinguished optically and by their powder patterns. The unit cell volumes increase in the order tetranatrolite, ranite, gonnardite and paranatrolite, therefore if the 1040 (or 1460) line can be identified in the powder patterns one can distinguish between these minerals. New infrared spectra of gonnardite, ranite and tetranatrolite are compared with each other and with published spectra, and differences are noted. DSC results for gonnardite and ranite are compared and appear to be diagnostic.

High-quality powder X-ray diffraction data for a well-characterised natural sample of natrolite (Na2Al2Si3O10.2H2O, space group Fdd2, Z = 8) are presented. Refined cell parameters were a = 18.2984±0.0007 Å, b = 18.6502±0.0008 Å, and c = 6.5589±0.0003 Å. The sample was characterised using thermogravimetric techniques (to determine water content), EPMA and ICP-MS (to determine composition). Available data suggest that the crystal matches the expected stoichiometry of natrolite. Our powder data show close similarity with the proposed structure of natrolite using the Rietveld method, giving R values of 8.54%, and suggest that preferred orientation is not present in the sample.