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 complex pore space considerably affects the unique properties of diatomite and its significant potential for many industrial applications. The pore network in the diatomite from the Lower Miocene strata of the Skole nappe (the Jawornik deposit, SE Poland) has been investigated using a fractal approach. The fractal dimension of the pore-space volume was calculated using the Menger sponge as a model of a porous body and the mercury porosimetry data in a pore-throat diameter range between 10,000 and 10 nm. Based on the digital analyses of the twodimensional images from thin sections taken under a scanning electron microscope at the backscattered electron mode at different magnifications, the authors tried to quantify the pore spaces of the diatomites using the box counting method. The results derived from the analyses of the pore-throat diameter distribution using mercury porosimetry have revealed that the pore space of the diatomite has the bifractal structure in two separated ranges of the pore-throat diameters considerably smaller than the pore-throat sizes corresponding to threshold pressures. Assuming that the fractal dimensions identified for the ranges of the smaller pore-throat diameters characterize the overall pore-throat network in the Jawornik diatomite, we can set apart the distribution of the pore-throat volume (necks) and the pore volume from the distribution of the pore-space volume (pores and necks together).

The sandstones with a laminated structure are common building materials. Lamination is macroscopically expressed as colour and grain size variations observed both in the deposit and within individual beds; therefore, the properties of such sandstones are diverse depending on the spatial distribution of the binding mass and framework components. For the terrestrial sandstones of different genesis, four types of laminae have been distinguished based on petrographic studies. They have a siliceous binder or a mixed ferruginous–siliceous–argillaceous binder with different proportions of these components. In laminae of types I–III, the grain framework is built mainly of quartz grains, and in type IV, it is accompanied by numerous lithoclasts and feldspars. Knoop hardness and CERCHAR abrasivity were tested in each lamina variety, and the results were correlated with the equivalent quartz content and the longitudinal ultrasonic wave velocity measured perpendicular and parallel to the lamination. The proposed research methodology was not used in previous studies on terrestrial laminated sandstones. The results explain a strong dependence between mineral composition, structure of laminae, and technical parameters of rocks. The knowledge of this relationship facilitates the selection of rocks that meet the relevant technical requirements and helps to optimally manage the resources of sandstone deposits.

Microstructural changes in flamed slabs of igneous rocks.

As so ci ate ed i tor: Wojciech Drzewicki Micro hard ness tests were car ried out on sin gle ha lite crys tals. They were con ducted on the (001) sur face, with the in denter set in two di rec tions: par al lel to the ha lite face (010); and par al lel to the (110) face. The ha lite crys tals rep re sent salt for mations of dif fer ent ages (De vo nian, Zechstein, Badenian), depths (from 1835.5 to 195 m) and in ten si ties of tec tonic dis turbance (hor i zon tally strat i fied, salt dome, strongly folded). The mea sure ment re sults re vealed spe cific fea tures of the ha lite crys tals ana lysed. Firstly, the data ob tained show micro hard ness ani so tropy in ha lite crys tals. More over, micro hard ness corre lates with the depth of the salt-bear ing for ma tions. Ha lite crys tals from deeper lev els showed higher micro hard ness, though there was no cor re la tion be tween the in ten sity of tec tonic de for ma tion and the av er age Vickers hard ness (HV). The sam ples ana lysed show a vari abil ity of HV val ues and and of the shapes of im prints. These in di cate zones where ha lite crystals are de formed at the atomic level and re flects the pres ence of de fects in the crys tal lat tice. Such de for ma tion is re flected in an ir reg u lar ity of the strike of cleav age planes. Con se quently, the anal y sis of im print shapes is a use ful method for the exam i na tion of duc tile min er als and ma te ri als. Key words: micro hard ness, ha lite, salt for ma tion, crys tal de fects, dis lo ca tions, shape of im print.