Spinel chromowy w masywie Gogołów–Jordanów w południowo-zachodniej Polsce występuje w zserpentynizowanym perydotycie, który buduje część kompleksu ofiolitowego Ślęży. Charakter chemiczny spinelu chromowego wskazuje na pochodzenie skał ofiolitowych ze zubożonego perydotytu plaszcza o składzie harzburgitu i podrzędnie dunitu. Skały płaszcza utworzyły się pierwotnie na grzbiecie śródoceanicznym i subsekwentnie zostały zrzucone w strefie supra-subdukcyjnej. Spinel chromowy często wykazuje strefowość optyczną i geochemiczną. Od jądra do brzegów można zaobserwować trzy strefy: wewnętrzne jądro o pierwotnym składzie spinelu chromowego; wąską strefę ferrochromitu bogatego w Cr; zewnętrzną strefę magnetytową. Strefowość spinelu chromowego jest interpretowana bardziej jako wynik serpentynizacji niż procesów magmowych czy metamorficznych. Dane geochemiczne dla chromitu i spinelu chromowego przedstawiono tabelarycznie. Zaobserwowano dwa trendy w odniesieniu do spinelu chromowego. Pierwszy przedstawia redystrybucję kationów trójwartościowych, gdzie Cr2O3 i Al2O3 zmniejszają się od pierwszej strefy do trzeciej. Drugi trend wskazuje na wzrost kationów Fe2O3 of strefy pierwszej do trzeciej. W spinelu chromowym znaleziono nieliczne inkluzje siarczków Ni i Cu, niestety zbyt małe do analiz EPMA.
EN
The chromian spinel of the Gogołów–Jordanów Massif, southwestern Poland, is hosted by a serpentinized peridotite that builds a part of the Ślęża ophiolite complex. The chemical character of the chromian spinel indicates that the ophiolitic rocks were derived from depleted mantle peridotite of harzburgite and subordinate dunite compositions. The mantle rocks were initially formed at a mid-oceanic ridge and subsequently thrust at a supra-subduction zone. The chromian spinel frequently displays optical and geochemical zoning. Three zones can be identified from core to edge: inner core representing the original composition of the chromian spinel; narrow Cr-rich ferrichromit zone; and outer – magnetite zone. The chromian spinel zonation is interpreted to be a result of serpentinization rather than magmatic or metamorphic processes. Geochemical data obtained from the chromitite and chromian spinel have been shown in a table. Two trends were achieved considering the chromian spinel. The first trend shows redistribution of trivalent cations, where Cr2O3 and Al2O3 diminishes from the first zone up to the third zone and the second trend indicates Fe2O3 cations that increase from the first zone up to the third zone. Few Ni and Cu sulfide inclusions were found in the chromian spinel, too small to take EPMA data.
During exploitation of serpentinite in the Nasławice quarry (SW Poland) a nephritic zone has been identified. Nephrite occurs in association with light in color rock, similar to rodingite, composed almost entirely of garnet. These rocks form oval bodies in serpentinites. Their maximal length is 7 m and height is 3.5 m. Nephrite appears in the contact zone of one of such bodies. In the upper contact zone nephrite is 10-15 cm thick and in the west side of the rodingite body reaches 40-50 cm. It is possible to distinguish varieties of nephrite from the Nasławice quarry which differ according to color, fabric and mineral composition. Nephrite from Nasławice is hard and reveals splintery fracture. Nephrite is mainly composed of actinolite, which forms fine- grained aggregates (length of fibres ca 100 um) arranged chaotically. Additional minerals also occur such as chromite, garnet enriched in Cr and pyroxene. Microscopic examination reveals that nephrite has massive, fibrous texture. With regard to gemmological properties, three varieties of nephrite have been identified: 1) Homogenous green nephrite with a small amount of chromite inclusions, which cover no more than 5% of surface of sliced samples; 2) Spotted nephrite-with numerous dark spots on a green background; it happens occasionally, that this variety of nephrite changes into serpentinite; 3) Patchy nephrite- characterized by the presence of emerald-green, elongated spots of actinolite (often with grains of chromite inside) on a white background; some fragments contain veins of fibrous serpentine with cat’s eye effect; this seems to be the most interesting sort of nephrite from Nasławice. Based on preliminary technological studies it can be concluded, that nephrite from Nasławice has not only a fine color and interesting texture, visible in sliced samples, but it is also easy for polishing. On polished surfaces nephrite shows fine oily luster. Unfortunately, examples found today are strongly cracked because of the explosive method of serpentinite exploitation used in the Nasławice quarry. The zone of nephrite occurrence is associated with the course of veins of leucocratic rock which extends over a distance of ca 5 km between Nasławice and Jordanów Sląski.
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