Ultramikroskopowe badania minerałów w związku z ich genezą

Stanisław J. Thugutt

Abstract


Ultramicroskopic investigations of minerals with regard to their origin

The long disputes of the plutonists and the neptunists may be an illustration of the fact, that the problem of the origin of minerals is not easy one. It should be added that, except fire and water, still other factors come into play, among these no small part is played by organisms. And it is characteristic that the smaller the organism, the more potent may be its action. Therefore much attention has been given lately to biogenic factors. It may be enough to mention the Spanish pyrites from Rio Tinto which form enormous lenses among phyllites and tuffites cut in many ways by eruptive rock intrusions. At first these pyrites were regarded as magmatic deposits, later as sediments, now a participation of anaerobic bacteria is suspected (1). Feicht and Foste r (2) ascribe to bacteria also the genesis of the Pittsburgh pyrites appearing in concretions of brown coal. The morphological characters are not always a sure indicator for the discussion of the origin of minerals. Bipyramidal quartz in eruptive rocks, reckoned until not long ago as a typical magmatic mineral (3, 4), in some cases appeared to be a hydrothermal form (5). When hydrogenesis of minerals is discussed, inclusions of water have a more essential meaning. Wheri they lack, the disperse phase may be a valuable indication, as it is visible in the ultramicroscope as submicrons or amicrons, if the latter’s diameter does not fall below 6 [x(x. Thç investigations performed comprise only minerals insoluble in water, because the soluble ones (as well as the minerals of magmatic origin) do not contain the disperse phase. Peter Baertschi (6) proposed lately a somewhat complicated method of the oxygen isotopes to distinguish magmatic rocks from the metasedimentary ones. The content of oxygen amounts to 50% in the earth’s crust, and at 500 atoms of the lighter isotope (016) fall against one atom of the heavier isotope 018. The sedimentary rocks always contain more heavy oxygen than the magmatic ones. Hence the possibility of establishing thé origin of the investigated material with the help of a mass spectrograph. Taking into account the presence of rests of the colloidal phase, hydrogenetic origin was ascertained for Marmarosz diamonds, Czech hyalite, quartz from the Carrara marbles, opalizing quartz from Brasil, milky quartz from Bronisławka, a quartz erratic from Nagorzany. Again, the quartz crystals from granite of the Erzgebirge, trachyte from Perlenhard, the Gothard protogine, dacite from Transsylvania, and the lechatellierite from fulgurite of the environs of Radom, were free from the disperse phase (7). In normal temperatures the colloidal solutions are not concentrated. At a temperature of ± 220° С and at a convenient pressure only 6 decigrammes of quartz dissolve in 1 litre of distilled water. As the temperature and the mass of acting water grow, the solubility of minerals increases distinctly (8). The possibility of obtaining colloidal solutions at a tempetature ± 200° С by simple contact of the pulverised solid phase with the solvent was ascertained on quartz, calcite, aragonite, orthoclase, albite, natrolite, apophyllite. leucite (9), lublinite, cassiterite, chalcedony, baryte (10). Attempts in analogical conditions undertaken with Volhynian labradorite from Horoszki did not give satisfactory results; no trace of albitization was observed, the hydrolysis was faintly marked and went in a completely different direction from the expected one (11). In nature, a factor intensifying the degree of dispersion and facilitating the access of water by the same is the presence of bacteria. They absorb some elements, give away others. E. g. milliards of such beings form millions of tons of opal at the bottom of water reservoirs and on the surface of the earth’s crust (12). Bacteria excrete carbon dioxide and some organic acids. Their action on phosphates or sulphates was ascertained many times. The bacteria attack the strong bases of silicates. According to K. Bassalik (13) the greatest activity in this direction is shown by Bacillus extorquens. From the twelve silicates submitted to his experiments biotite was especially susceptible, and in succession after it nephelite, muscovite, leucite, while olivine was least susceptible. Orthoclase took a position so to say intermediate, as it was much less attacked than leucite and nephelite. It is true that the degree of saturation of the colloidal solutions increases considerably with temperature; but as the specific gravity of the solid phase increases its solubility in water gradually decreases. Experiments undertaken (14) ascertained that at a temperature ± 200 degrees С:
chalcedony density 2,625 forms a solution 0,126 per cent
quartz density 2,65 forms a solution 0,062 per cent
fluorite density 3,179 forms a solution 0,00296 per cent
baryte density 4,5 forms a solution 0,00126 per cent
cassiterite density 7,0 forms a solution 0,00026 per cent
Aragonite (density 2,934) is an exception, as it forms a water solution 2,4 times stronger than calcite with its density 2,715 (15). For the new ultramicroscopic investigations a Leitz microscope was used (objective III and eyepiece III) with a Spencer dark field lluminator constructed by the American Optical Company in New York. In the first place var ious forms of silica were examined. As said before, the quartz crystals of hydrous origin always show the presence of the disperse phase. I found it, too, in «hooded» quartz appearing in a mighty fluorite-quartz vein from Kopalina in Lower Silesia, and also in quartz lying on chalcedony in a melaphyre geode from Siemiota near Alwernia (district Cracow) as well as in quartz from the Aggtela grotto in Hungary1. However, there was none of it in the rounded grains of magmatic quartz belonging to the Lower Dewonian quartzites of the Kielce—Sandomierz chain from Grzegorzewice near Nowa Słupia, as well as in the Tkanów quartzite from the environs of Opatów, and the quartzite sandstone from Mt. Tomanowa (Tatra Mts.). The blotty, thick-grained, and cross-bedded sandstones from Mt. Tomanowa contained both kinds of quartz grains, with the disperse phase and without it, bringing a clear testimony as to the dual origin of these grains. The distinction of the hydrogenic quartz ß from its magmatic variety a becomes highly facilitated by ultramicroscopic examination. Graphic grani t e Taking into consideration the relative facility of watery solution in a colloidal form of quartz together with orthoclase as well as the mutual relation of these two minerals in the solutions (16), I concluded that the graphic granite is not an exclusively magmatic product (against the statements of Till, Vogt, Brögger, Fersman) but that it may crystallize from a watery solution, too. This was completely confirmed by examinations of graphic granite from the Ilmenian Mts. of the Ural. The ultramicroscope showed a considerable content of the disperse phase especially in quartz and less in orthoclase. Already W. T. Schaller (17) drew attention to the possibility of a formation of the graphic structures in hydrogenic ways. According to Felix Machatschki (18), the similarity of the internal constitution of these two minerals helps to a great degree to their mutual crystallization. Investigations of the graphic pegmatites of the Stępniak district in northern Kazachstan (1949) induced T. M. Dembo (19) to call their quartz intrusions epigenetic forms, taking the place of the feldspar which crystallized earlier. The mutual relations of the said components was variable in the pegmatite, some crystals of the quartz were even idiomorphic and grew not only into microcline, but even into albite and andesine. Similarly, W. D. Nikitin (20) examining the pegmatites of southern Karelia (1949) ascertained that the graphic structures appearing there were not formed at once, but that they were preceded by the granite-aplite and granite-porphyry stages. The post-magmatic solutions intruding later changed the existing crystalline structure and caused the graphic form. The sodium silicates liberated during metasomatosis gavs beginning to the perthite forms. Then a second stage of formation of the graphic structures followed, connected with an exchange of the feldspars for quartz, with it came albitisation of the aplite and muscovitisation of the feldspars. In turn there appeared tourmaline, apatite, chromite (formed from biotite), magnetite, ilmenite, sphene, pyrite, chalcopyrite, calcite. The process of metasomatosis of the porphyry was at last terminated by sericitisation of both types of feldspars. Adular and microcline Gustav Tschermak (21), and before him already Volger and H. Rose, regarded the adular occurring in geodes and rock veins as a hydrogenic mineral. As the solubility of orthoclase in distilled water was ascertained later on, a valuable confirmation of this idea was gained. The obtained solution was of a colloidal nature and contained more silica than the rest undissolved in water. The supposition that we are in presence of a decomposition of the feldspar molecule into two links — an adular one with more silica and a microcline one with less silica — was not confirmed, because the presence of a mechanical admixture of ferric oxide was not taken into consideration. Anyway, the sodium-potassium feldspar contains — except two aluminohexasilicate links K(2)Al(2)Si(6)O(16) and Na(2)Al(2)Si(6)O(16) — a third ferrihexasilicate link R(2)Fe(2)Si(6)O(16). The latter, when hydrolysed, splits into ferric oxide (haematite or goethite) and an alkaline silicate which the water takes away (22). If this microclinic rest of the feldspar is submitted to a total analysis together with the ferric oxide, there results a deficit of silica, so often found in microcline of various origins. The composition of the adular component of the feldspar (carried away by the water) should not differ from the normal, too, if it had no addition of silica from the decomposed ferrihexasilicate link. Therefore the precise analyses of the adulars from Bg. d’Oisans and from Krimml performed by Eugenia Zaniewska-Chlipalska (23) showed an alumina: silica ratio higher than 1:6. In the remaining microcline the presence of an admixture of ferric oxide finds expression in its red colour. The disperse phase is absent here. It is shown only by colourless microclines, appearing on a secondary bed, as e. g. microcline from Mt. Kosista (Tatra Mts.). As regards the green colour of microcline called amazonite, we should note a paper published in 1949 by E. N. Eliseief (24). From the fact that amazonite loses its colour after heating to 500° С and regains it afterwards by irradiating with X-rays, this author concludes that the colouring agent is not (as supposed by Viernadskij , Goldschmidt and Kapustin) rubidium or some other rare element, but most probably bivalent iron; this is oxydated because of the heating and becomes trivalent, however, after X-ray irradiation returns to its former bivalency. The red microcline, containing no disperse phase, behaved indifferently when submitted to the same operations. The reason of this disappearing and reappearing of the green colour lies, in fact, elsewhere. Amazonite, as a secondary mineral, came to its bed as a hydrosol. Then, crystallizing, it conserved rests of its disperse phase which cause its colour (25). We see this on the examples of gold, silver, and other suspension solutions. As the diameter of the suspended particles decreases, the colour changes from yellow to orange, then red, violet, blue and green. The maximum of absorption shifts towards- the longer waves as the dispersion grows. The change of colour shown by allochromatic bodies under short-wave irradiation is caused by an increased dispersion of the colloid. Again, high temperature brings nearer the latter’s particles, causing their agglomeration which ends in a complete loss of colour. The pigment, standing in the way of short-wave rays, causes their diffraction and finds expression in colour if the wave-length of the falling ray equals, or is less than the particle’s size. Rays of different wave-length are differently deflected, only the larger waves go through without obstacle. I cannot unfortunately refer to the rich material of chemical analyses gathered in the works of Hintze and Do el ter to verify the reasoning pertaining to microcline. The papers quoted contain nearly no determinations of ferric oxide and barium. I can, however, quote an analysis of microcline from a pegmatite-aplite vein of the Klesow porphyrite performed by Eugenia Zaniewska-Chlipalska (26):
SiO(2) – 64,58
Al(2)O(3) – 18,92
Fe(2)O(3) – 0,32
BaO – 0,20
CaO – 0,32
K(2)O – 13,13
NaO – 2,70
H(2)O – 0,47
Sum – 100,64
In this analysis the ratio alumina: silica = 1:5,8. It happens sometimes that — independently of the quoted transformations — the albite link is leached away together with the orthoclase. This phenomenon was investigated very thoroughly by Elżbieta Stella-Litmanowiczówna (27). The aluminohexasilicate of sodium liberated from orthoclase either precipitates on the planes of cleavage of the potassium feldspar forming perthite intergrowths with it or is transported further by the water and fills free spaces of rock crevices. This is the origin of e. g. splendid incrustations in a pegmatite vein from Strzegom (Lower Silesia) composed of albite crystals with a small admixture of quartz. The problem of internal constitution of orthoclase together with the microcline formed from it shows grave difficulties according to Wilhelm Eitel (28). Max Reinhard and R. Bächlin (29) conclude upon a series of intermediate types between the triclinic untwinned microcline and the submicroscopically twinned apparently monoclinic orthoclase. According to A. Hadding (1918) the X-ray diagrams of these two minerals do not show differences, which is in conformity with their genetic relations discussed above. The high pressure referred о by E. Mäkinen (1917) is not necessary here. Plutonic rocks. We do not know plutonic rocks in their primary state. If we base on an analogical material of eruptive rocks and on laboratory experiments, we try to guess this state to a certain degree. In magmatic rocks we should await neither hydrous minerals nor the presence of the disperse phase. However, we must count with the possibility of later transformations, sometimes changing completely the physical and chemical characteristics of the primary material. If we find in magmatic rocks e. g. analcite, microcline, muscovite or amphibole, we have not yet the right to conclude upon their magmatic origin. We know that with a change of thermodynamical conditions the equilibrium of a system is disturbed. The rock, apparently impervious, inaccessible to chemical agents, slowly undergoes transformations. This action is seconded by the elastic constitution of the macromolecular silicate lattices and the indefatigable movement of the separate atom constituents. From orthoclase there emerges microcline, from biotite — muscovite, from leucite — analcite, from augite — amphibole. The orogenic processes facilitate the access of water, heightened temperature betters the action’s efficiency. Water intruding into the fissures of fractured quartz leaves there its traces in the form of numerous grains of disperse silica. Such agglomerations of the disperse phase along the fissures of quartz crystals are to be seen e. g. in the granite from Ramberg (Harz Mts.), in the Swedish granite from Uppsala, in the diorite from Adamello (eastern Alps), in the granitic porphyry from Bodwin Mulberry in Cornwall, in the granitic porphyry from Altenberg in Saxony. The content of the disperse phase was strikingly large in the quartz porphyry from Miękinia near Krzeszowice (district Kraków) investigated by Zygmunt Rozen (30). This is a holocrystalline rock. Among the phenocrysts there appear — besides plagioclase, biotite, and eventually amphibole — chiefly orthoclase and less numerous corroded quartz. The rusty-red-coloured rock has an un-fresh look. The disperse phase appears only in the quartz crystals, evenly distributed, penetrating the whole of the crystal. One has the impression that the Miękinia porphyry is as if a congealed volcanic tuff (which, by the way, is not rare in the region) into which silica penetrated as free spaces tuff. This explains, too, the xenomorphism of the quartz crystals, which is regarded by Rozen as a symptom of magmatic corrosion. In the Tatra pegmatites from Mt. Kasprowy Wierch, examined by Władysław Pawlica (31), the disperse phase appears not only in the quartz crystals but in both the micas and in red orthoclase as well; only the crystals of plagioclase and tourmaline are free from it. A great amount of the disperse phase was found in quartz in the aplite from Sicamus in British Columbia and also in quartz forming a component of the Finnish granite from Abo. Volcanic rocks examined for comparison, as the trachyte from Mont Dore, the sphaerolitic liparite from Hlinik in Slovakia, did not show the presence of the disperse phase in the quartz crystals. Mica group Biotite in magmatic forms should not contain the disperse phase. This is why none was observed in the biotites in the Swedish granite from Uppsala, in the granite from Ramberg (Harz Mts.), in the Tatra granite, in the quartz diorite from Adamello (eastern Alps). Biotite is not durable naturally and easily submits to the action of water and watery solutions which leach away its aluminobisilicate of potassium. Thus a common product of the transformation of biotite is muscovite, often reckoned as a syngenetic form with biotite. The right or wrong of this assertion may be proved by the use of the ultramicroscope. The beginnings of the muscovitisation of biotite are marked initially by the presence of small amounts of the disperse phase. We see it e. g. on a specimen from Merefjord in Norway, or in a biotitegarnet shale of unknown origin. In the end stage the disperse phase fills the entire crystal, as seen e. g. in muscovite from Bensas in India or in Tatra muscovite from Mt. Kasprowy Wierch. In the series of anhydrous silicates a large amount of the disperse phase is contained in Tyrolese dysthene from Pfitsch, in Finnish cordierite from Orijärvi, as well as a partly transformed leucite from Mt. Vesuvius and leucite from Rocca Monfina. I did not notice any disperse phase in grossular from Dognacska in the Banat, in Tyrolese andalusite, and in wollastonite from Berggiesshiibel in Saxony. Among the pegmat i te forms sapphire-coloured sodalite from Turkestan (by Zarafshan) and pink tourmaline from Ceylon were distinguished by a great plenty of minutely disperse phase. S. W. Grum-Grzymaj ło (32) basing on spectrometric measurements of light absorption by tourmalines of various origin, supposed that the pink colour is caused by trivalent manganese coordinated six times. However, this author did not observe the awaited dependency of the colour intensity with the manganese content, supposedly because of the various degrees of oxidation of the latter. Namely, the disparition of colour of the tourmaline at a temperature of 400° С was to be caused by a change of valency of manganese Mn(2)O(3)->MnO and the simultaneous oxidation of iron FeO->Fe(2)O(3). I think it would be more proper to connect the pink colour o f tourmaline with the disperse phase, as was done with the green-coloured amazonite. In the group of hydrous silicates the disperse phase was particularly copious in secondary-bed zeolites; in their number was chabasite from Markersdorf in Bohemia, analcite and scolezite from Fassa Valley in Tyrol. In Islandie desmine from Berufjord it was less plentiful. Again, large amounts of it were found in apophyllite from Guanajuato in Mexico, in cancrinite from Litchfield in Maine, and in Norvegian epidote from Arendal. In Tyrolese chlorite from Zillertal there was comparatively not much of it, still less in green troubled prehnite from the Cape of Good Hope. There is no doubt that the troubled background of the prehnite much weakened the visibility of the minutely disperse phase. Carbonates The origin of carbonates, and especially of calcium carbonate is connected with the life of organisms. Here — except corals, crinoids, molluscs, and snails — an active part is played by unicellular water plants, coccolites (33), and bacteria (34). According to Henning Il lien (35) numerous concretions of ferrous sulphide in the southern- Baltic Cretaceous testify that microbial life processes had a part in the sedimentation of writing chalk. Drew (1914), Nadson (1928), Brusof f (1932) paid special attention to the action of thermophile bacteria (36) which absorb and excrete calcium compounds, while the transformation of the molecularly disperse phase into colloidal hydrosol is supposed to happen in a continuous manner. The colloidal solutions of the carbonates play a comparatively very small part in nature. The solubility of calcite in a colloidal state at a temperature of 200° С is expressed in thousandths of a percent only (0,00484). The solubility of aragonite is 2,4 times greater (37). With the temperature the solubility of the carbonates increases considerably, this may have greater importance under the surface of the earth. The waters circulating there carry the carbonates into numerous rock fissures and form in places the alternate layers of calcite and aragonite, so mysterious for H. Credner (38). On the other hand, the form in which calcium circulates in nature is the real solution of calcium bicarbonate. The products of the crystallization of real solutions do not contain the disperse phase. I found none, too, in the calcite from Andreasberg in the Harz Mts., in the marbles from Stolberg or Kielce, in the aragonite from Herrengrund in Hungaria, in the crystals of dolomite from Pribram and Salzburg. Chlorides and fluorides Thanks to the basic studies of van’t Hoff the conditions of the formation of salt deposits in nature are thoroughly known. The only troubling problem remained the colour of halite. There were attempts to produce this colouring artificially. In 1885 E. Becquerel (39) irradiated colourless halite with cathode rays obtaining a brownish tinge. The same was done afterwards by C. Doelter (40) who obtained a blue tinge, however, only on the crystal surface. In 1892 F. Kreutz (41) heated halite in sodium vapour; the salt took a blue colour. H. Siede ntopf (42) basing on ultramicroscopic observations ascertained that the said colour is caused by a dispersed pigment, in places concentrated cloudwise, in places disposed parallelly to the faces of the cube or to their diagonals. It was found later that the salt artificially coloured has other properties than the natural one (e. g. it reacts with water in the alkaline direction, the natural salt does not), it shows, too, a different absorption spectre and behaves differently in a heightened temperature and during X-ray irradiation. Thus the problem of the colour of blue salt remained open. I undertook it again with the help of the ultramicroscope. The colourless, immaculately transparent halite from Bochnia and Wieliczka contained no disperse phase, except small impurities. Again, the blue halite from Kałusz contained much of it, however irregularly dispersed. It does not result from this that metallic sodium should be the colouring agent, as was supposed. It could be as well colloidal silica as colloidal alumina or colloidal ferric hydrate. And really, traces, of ferric hydrate are found in blue salt by F. Kreutz in 1892, and after him the same observation is made by J. Bruckmoser. As the colour is decided upon not by the nature, but by the degree of dispersion of the solid phase, the solution of this problem is to be searched far here. Fluorite The conditions in which fluorite appears in nature are rather varied. Fluorite is found in ore veins together with baryte, quartz, chalcedony, calcite, moreover in sandstones, sandstone breccias, dolomites, mylonite, as the cement of granite fragments. Fluorite forms pseudomorphoses after calcite, baryte, galenite. Again, the form of fluorite is borrowed by sphalerite, pyrite, quartz, and many other minerals. Sometimes fluid inclusions appear, in spite of the supposed insolubility of fluorite in water. The watery solution of fluorite exists, but it is a colloidal one, hardly 0,00296 percent (43). The problem of the changing colour of fluorite is strictly connected with the existence of its disperse phase. The most varied suppositions were made in this direction. It was believed that the colour is caused by organic compounds, as calcinated fluorite loses its colour. With the moment, however, that the lost colour was recovered by cathode ray irradiation, inorganic bodies were taken into account. The colouring agent was to be fluorine or metallic calcium. And really, colourless fluorite after heating in calcium vapour takes a blue colour, however, with water it gives an alkaline reaction which is not the case with natural fluorite. Moreover, the colour of artificially coloured fluorite is stable and disappears only at 720° C, while natural fluorite loses it already at a temperature of 240° C. In respect to the short-wave rays fluorite behaves similarly to halite,: the degree of dispersion of the colloidal phase increases, finding expression in colour. Again, heating causes agglomeration of the colloidal phase, ending in a complete loss of colour. Fluorites connected with volcanic phenomena are colourless and contain no disperse phase. The fluorite appearing in the background of a quartz vein of hydrous origin from Kopalina in Lower Silesia did not show the presence of the disperse phase, thanks to the numerous fissures caused by the mounting of the slide on hot Canada balsam. Sulphates Baryte found in ore veins forms coagulates, botryoidal stalactitic masses, concretions with foraminifers and radiolaria, on the sea-bottom it accompanies manganese nodules, in sandstone it takes the character of cement, it forms pseudomorphoses after calcite and dolomite, sometimes on the contrary leaving its place to calcite and dolomite. The means of these transformations, however, are not known. The investigations of its solubility in pure or salt water gave no satisfactory results. A real solution of baryte in water does not exist. Again, at 206° С a colloidal solution in water may be obtained, 0,00126 percent only, it is true (44). In this form baryte may wander in nature and colour its own crystals! According to Maria Kołaczkowska [Arch. Min. Tow. Nauk. Warsz. 12 (1936)] the appearing of colour may be explained by regrouping of particles, dispersed confusedly in the baryte crystal, and their ordering in regard to the lattice constitution of the crystal. While observing under the ultramicroscope, I could find the disperse phase neither in a baryte coagulate from Saxony, nor in a crystal from Jaworzno (Silesia), because of the fissures caused by heating of the slide while mounting it on the object glass. The anhydr i te from Wieliczka examined at the same time was filled copiously with the disperse phase. According to Ei lhard Schulze (45) — except algae as Fucus vesiculosus — chiefly protozoa of the family Xenophyophora take a part in the concentration of baryte on the sea-bottom. Sulphides Among the sulphides the omnipresent pyr i te is most universally distributed. Pyrite may be a direct product of the crystallization of magma, it forms crusts in volcanic craters, the most important, however, are the deposits appearing among sedimentary rocks. Here the deposits of pyrite sometimes reach tremendous sizes. The deposit of Rio Tinto is estimated about 400 milion tons. A. Lacroix (47) reminds that pyrite forms the sediments of many thermal waters in France as well as Algiers. Pyrite impregnations appear in clay and alumen shales, in marls and limestones, in coal and lignite deposits. We know pseudomorphoses of pyrite after galenite, fluorite, baryte, magnetite, so that the hydrogenesis of pyrite seems indubitable. After C. Doelter (48) water solves 0,10 percent of pyrite at a temperature of 80° C. O. Weigel who investigated electrical conductivity found 48,89.10—8 mol of pyrite in 1 litre of water. This was surely no real solution, but a coloidal one, easily recognisable in the ultramicroscope. Thus I ascertained the presence of the disperse phase in pyrite from the Carpathians, in crystals of pyrite covering a quartz vein in shale from Monte Catini, in a pyrite nodule covered by a coating of golden-coloured from the St. Croix Mts. Various suppositions werem ade in regard otf he latter deposit. Franciszek Bieda (49) expressed the idea that the pyrite probably sedimented in veins cutting Devonian rocks, but which originated much later as a result of the action of gases and vapours from volcanoes active in the post-Devonian periods of the earth’s history. Czesław Poborski (50) took the deposit for an epigenetic form of hydrothermal origin connected with the dislocation zone composed of faults; one of the latter goes through Rudki. The dislocation fissures were the way through which the solutions ascended and gave origin to the deposit in the Lower Permian. According to Czesław Kuźniar (51) the deposit would be formed in several stages: first stage — dolomitisation, second stage — sideritisation, third stage — haematitisation, fourth stage — pyritisation or metasomatosis of dolomites or siderites caused by sulphide solutions, while the dolomites were transformed into black loams or loamy shales. Karol Bohdanowicz (52) saw two phases of mineralisation in the Rudki deposit: «after the phase of pyritisation, it seems, a rejuvenation of the deposit took place, as well as a phase of sideritisation, or perhaps vice versa. The relation of pyrite to marcasite is unknown, too, as well as that of the rocky pyrite to the powdery one». If we take into account the oolite-sphaeric structure and the presence of the disperse phase in the pyrite, we must acknowledge that the deposit is a hydrogel formed in special conditions. The action of pyritisation — as witnessed by the dolomites surrounding the ore — must have taken place in the littoral zone of a shallow sea in ooze and slime transformed later into the clay shale and black loams around the deposit. Just as in the slime of the contemporary limans, micro-organisms must have acted there in the Permian period forming ferrous monosulphide from sulphates and decaying organic rests covering the sea-bottom. This sulphide, taking in sulphur, changes at first into a mielnikovite gel (55) and then into powdery or crystalline pyrite, according to the conditions. The iron supplied by siderite, which is strictly connected with dolomite and is a product of its metasomatosis. According to C. Doelter (56) the microorganisms cannot form large quantities of pyrite, as they appear at a depth of 4 do 5 metres as a maximum. Meanwhile Vernadskij (57) communicates that in coal beds anaerobic bacteria were found alive at a depth of 400 to 1090 metres. Similarly, E. Bastin (58) in northern America and N. Ushinskij (1929) in oil-bearing waters of the Apsheron peninsula near Baku found live bacteria at a depth of more than 1 kilometre. This would suffice completely to understand the origin of a pyrite deposit even as enormous as the Spanish one of Rio Tinto. This deposit lies on a former seashore corresponding to the contemporary course of the river Rio Tinto. The background of the deposit, which is devided into 50 enormous lenses cut by faults, is made of ooze and sea slime transformed slowly into phyllites and loamy, chlorite, and sericite shales of the palaeozoic age. In this series lie intrusions of various porphyries touchnig the pyrite in places. The pyrite shows a xenomorph constitution, massive, fine-grained. When it still was in a hydrogel state, it impressed into surrounding rocks, sometimes wedging out fingerwise. Sulphide of zinc appears in eruptive rock veins, in sediments, in crystalline shales, as regular sphalerite or hexagonal wurtzite. According to C. Doelter (59) only 0,048 percent of the sphalerite goes into watery solution. The nature of this solution was not investigated by Doelter. The reniform structure often met with as well, as the ultramicroscopical examinations indicate the colloidal state of the solution. Plenty of the disperse phase is contained in Czech wurtzite from Pribram. In sphalerite from Silesia, of a very fine-grained structure, no shining dots (characterising colloids) could be noticed. Dr Krusch (60) investigating the Silesian zinc deposits ascertained their epigenetic character. The origin of the deposit is connected chiefly with colloidal phenomena occurring at a temperature not exceeding 100° С. In places the middle part of the earthy deposit transforms slowly into crystalline wurtzite, which sets at the bottom and at the top of the deposit going through the rock. Вastin (1926) connects the origin of zinc sulphide with the activities of anaerobic bacteria which reduce sulphates and produce hydrogen sulphide; the latter forms zinc sulphide when contacting with chloride or carbonate of zinc. The descriptions quoted are far from exhausting the subject, they have rather an orientating character. Further research should be based on material precisely analysed, with a most detailed consideration of the conditions of appearance of the specimens in nature.

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