Agate samples collected from the vicinity of Asni and Agouim (Western Atlas, Morocco) were investigated using microscopic observations supported by Raman micro-spectroscopy. The agates are marked by the presence of various microtextures typical of epithermal vein deposits, including jigsaw-puzzle, feathery, and lattice-bladed. The first two indicate that the formation of agates was likely marked by recrystallization of metastable silica phases (i.e., opaline silica or massive chalcedony). The presence of lattice-bladed (after barite and calcite) quartz may be, in turn, ascribed to the boiling-related conditions that could have triggered the formation of abundant copper and iron sulfides found within silica matrix. Additionally, the local occurrence of growth lines (so-called Bambauer quartz) and intergrowth of length-slow and length-fast chalcedony are linked to the variations of physico-chemical conditions during rock formation (alkaline-acidic). According to Raman spectroscopy, silica matrix of the agates is made of α-quartz with a local admixture of moganite (from 0.0 up to 78 wt.%), but also contains numerous solid inclusions of hematite, celadonite, as well as poorly-organized carbonaceous material and rutile. These phases were likely emplaced during low-temperature hydrothermal activity of SiO2-bearing fluids that originated from post-magmatic hydrothermal activity developed within host rocks and/or meteoric waters.
Diatomites belonging to a list of raw materials used in the EU criticality assessment are essential to many industrial applications due to a unique combination of their physical properties, i.e. porous and permeable structure, high specific surface area and adsorption capacity, low density and thermal conductivity, and chemical inertness. The present study was undertaken to analyse the relationships between the pore network characteristics, petrophysical parameters, and mineralogical variability of the Lower Miocene diatomites from the Jawornik deposit (Skole Unit, the Polish Outer Carpathians, SE Poland). Five varieties of the diatomites, distinguished on the basis of the macroscopic features, i.e., colour and fracturing effects, have been investigated by SEM, chemical and XRD analysis, mercury intrusion porosimetry, helium pycnometry, and the Vickers hardness tests. Significantly differing are two varieties. The light-coloured, massive and block-forming diatomites (variety BL) consist mainly of poorly cemented siliceous skeletal remains of diatoms, and represent the rocks with high total porosity (38-43%), low bulk density (1.28-1.38 g/cm 3) and low microhardness (10.7 HV 0.3). The dark-gray silicified diatomites with a platy or prismatic splitting (variety PD) reveal obscured microfossils of diatoms and are the most compact and hard rocks (80.8 HV 0.3), with poor total porosity (17-24%) and higher bulk density (1.70-1.78 g/cm 3). The spatial distribution of the field identifiable rock varieties allows selective exploitation of the diatomites with the predictable petrophysical characteristics that define their future use.
The oc cur rence of both the blue and vi o let halites is one of the most in ter est ing phe nom ena in na ture. De spite nu mer ous labo ra tory and field works, their or i gin in nat u ral evaporitic en vi ron ments has not been sat is fac to rily ex plained. In the K³odawa Salt Dome (Zechstein, Cen tral Po land), blue or vi o let halites oc cur rel a tively fre quently. Their ac cu mu la tions dif fer in size and in ten sity of colours. In this pa per, pet ro log i cal fea tures of anhydrite crys tals de rived from one of the larg est out crops of the blue ha lite at the K³odawa Salt Mine are pre sented. Anhydrite is one of solid in clu sions en coun tered in blue-col oured halite crys tals. Spe cial at ten tion was paid to fluid in clu sions pres ent in this anhydrite. The microthermometric mea sure ments showed two di rec tions of ho mog e nisation, i.e., to wards the liq uid phase (LG®L, LL®L) or to wards the gas phase (LG®G). In the for mer case, the tem per a tures ranged from 174 to 513°C, whereas in the lat ter one, the val ues from 224 to 385°C were mea sured. The com po si tion of in clu sions is rel a tively vari able. We can ob serve trans par ent and opaque daugh ter min er als as well as CO 2 in the liq uid phase ac com pa nied by a vari able amount of meth ane or hy dro gen sul phide. These fea tures of inclu sions in di cate that anhydrite crys tals and, thus, blue ha lite were formed un der the in flu ence of hy dro ther mal con di tions. Ob ser va tions in the mine work ings com bined with pet ro log i cal stud ies en able to con clude that blue colouration of ha lite crystals is con trolled by three fac tors: a high tem per a ture, re duc ing con di tions and de fects in ha lite lat tice re lated to tec tonic stress.Key words: blue ha lite, hy dro ther mal en vi ron ment, salt domes, anhydrite, epigenetic salt.
Wachowiak, J., Tobo³a, T., 2014. Phase tran si tions in the bo rate min er als from the K³odawa salt dome (cen tral Po land) as indi ca tors of tem per a ture pro cesses in salt diapirs. Geo log i cal Quar terly, 58 (3): 543-554, doi: 10.7306/gq.1170The diapiric struc tures of the Pol ish Low lands are tec toni cally deeply seated down to the autochthonous Zechstein strata at a depth of ca. 6 km. In the pro cess of deep burial and halokinetic diapirism, the salt rocks were sub jected to diagenetic and meta mor phic trans for ma tions, with the tem per a ture be ing an es sen tial fac tor. Con sid er ing the ther mal gra di ent, a tem per ature of up to ca. 200°C can be achieved in the salt dome within a depth range from sev eral hun dred metres to 6 km, which may lead to trans for ma tions of the ma jor ity of salt min er als. Phase tran si tions of two bo rate min er als -boracite and congolite from the K³odawa salt dome -pro vide ev i dence for higher tem per a tures in the salt dome rocks. The authigenic euhedral crys tals of those bo rate min er als dis play their ex ter nal habitus in am bi ent tem per a ture in the form of reg u lar sym me try (F43c -pseudo-reg u lar poly he drons), whereas their in ter nal struc ture is lower: orthorhombic (Pca2 1 ) for boracite and rhombohedral (R3 C ) for congolite. The heat ing and cool ing of boracite and congolite crys tals show re vers ible phase tran si tion. At a tem per a ture of ca. 270°C, boracite crys tals change their sym me try: orthorhombic « cu bic. In the case of congolite three revers ible phase tran si tions within a tem per a ture range of 50-339°C can be ob served: rhombohedral « monoclinic « orthorhombic « cu bic sym me try. Those phase tran si tions, con firmed ex per i men tally in our study, clearly doc u ment at least lo cal oc cur rences of tem per a tures ex ceed ing 339°C in the K³odawa salt dome.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.