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Nefryt z Nasławic na Dolnym Śląsku

Łobos K., Sachanbiński M., Pawlik T.

Przegląd Geologiczny

2008

Vol. 56, nr 11

991-999

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.