Janus Pannonius Múzeum Évkönyve 43 (1998)( Pécs, 1999)

Régészet - Schléder, Zsolt–T. Biró, Katalin. Petroarchaeological studies on polished stone artifacts from Baranya county, Hungary

78 A JANUS PANNONIUS MÚZEUM ÉVKÖNYVE 41-42 (1996-97) Microscopic features. The first group of basalts can be characterised by porphyritic-intergranular, slightly trachytic texture and contains lots of relatively small olivine phenocrysts. Samples no. 4,16 belong to the first group of basalts. The second group of basalts can be characterised by porphyritic-intergranular, strongly trachytic texture and pyroxene phenocrysts. Samples no. 9, 10 belong to the second group of basalts. The third group of basalts can be characterised by porphyriticintergranular, slightly trachytic texture, big olivine phenocrysts, aegirine-augite and augite containing opaque minerals. Sample no. 17 belongs to the third group of basalts. Group 1. (samples no. 4, 16). Name of rock: basalt Texture: porphyritic-intergranular, slightly trachytic Mineral composition: olivine, pyroxene, plagioclase, apatite, biotite, sodalite, opaque mineral. Idiomorphic, 0.5-1 mm sized olivine turns into iddingsite. Skeletal crystals indicate rapid crystallisation. Idiomorphic, 0.10.2 mm sized augitic pyroxene has a y/c extinction angle of 40° and strong dispersion. Opaque mineral inclusions are frequent. Hypidiomorphic-xenomorphic, 0.125 mm sized plagioclase lath is the most frequent component. The composition is labradoritic based on Michel-Lévy extinction method. Apatite occurs as 0.1 mm long fibres, often as inclusion in plagioclase. Opaque minerals can also occur as inclusions. Sodalite is a rare component with a size of 25 um in the sample. I&omorphic-hypidiomorphic phlogopite occurs in a size of almost 0.1 mm. It is characterized by strong pleochroism and a 2V-angle of almost 90°. The space among the plagioclase laths is filled with rock-glass. Anisotropy indicates the beginning of crystallisation of the matrix (Photo Plate ÍV/3). Group 2. (samples no. 9, 10) Name of rock: basalt Texture: porphyritic-intergranular, strongly trachytic. Mineral composition: olivine, pyroxene, plagioclase, apatite, biotite, opaque mineral. Idiomorphic 0.25 mm large olivine fully turned into green iddingsite with slight pleochroism. Pyroxene rarely occurs as 1-1.5 mm large zoned, idiomorphic-hypidiomorphic tabular porphyritic grains. An augitic core is framed by 0.1 mm thick brownish Ti-augitic rim. The rim contains plagioclase and opaque mineral inclusions. In most cases, Ti-augitic pyroxene (the y/c extinction angle is 40°) occurs in the groundmass in a size of 0.25 mm. It is usually hypidiomorphic, sometimes xenomorphic. In this case, it fills in the remaining space among the plagioclases. The orientation of idiomorphic, 0.5 mm sized plagioclase laths indicates trachytic texture. Plagioclase composition is andesinic-labradoritic, based on Michel-Lévy extinction method. It rarely turns into chlorite or clay mineral. Idiomorphic, 50-100 urn longe apatite fibres can be found as inclusion in the plagioclase. Opaque minerals also occur as inclusions. Idiomorphic, 100 urn large biotite with strong pleochroism (colourless-brown) is a rare element. Opaque minerals also occur as skeletal crystals in a size of 0.25 mm. Their habit refers to ilmenite. They can contain inclusions of pyroxene and plagioclase. Rock glass among the plagioclase laths always turns into chlorite (Photo Plate VII). Group 3. (sample no. 17) Name of rock: basalt Texture: porphyritic-intergranular, slightly trachytic Mineral composition: olivine, pyroxene, plagioclase, apatite, opaque minerals. Idiomorphic, 0.25-0.5 mm (rarely 1 mm) sized skeletal crystals of olivine refer to rapid crystallization. Olivine begins to turn into iddingsite. The amount of pyroxene is higher than that of olivine. Idiomorphic, zoned pyroxene has a size of 0.125 mm. The core is mainly augitic, based on the 30° y/c extinction angle sometimes aegirine-augitic with greenpale green pleochroism, and the rim is Ti-augitic. Pyroxene always contains opaque mineral inclusions. Idiomorphic-hypidiomorphic plagioclase laths in a size of 0.125 mm is the most frequent element. The plagioclase composition according to Michel-Lévy extinction method is labradoritic. The idiomorphic, 25-50 urn large opaque minerals can be determined as magnetite based on their habit. The considerable accumulation of opaque minerals is caused by huge amphiboles turning into rhönite. Slight anisotropy of the rock-glass matrix refers to beginning crystallisation. The glass sometimes turns into clay mineral (Photo Plate VI2). Andésite Tool Nr. 14. was determined as andésite. Macroscopic features. The texture of the rock is porphyritic. Off-white, 1-2 mm large plagioclase Porphyrie grains can be seen in the fine grained grey matrix. Microscopic features. Name of rock: Andésite Texture: cumuloporphyritic-holocrystalline. Formerly pilotaxitic (the rock glass has turned to chlorite). Mineral composition: pyroxene, plagioclase, apatite, opaque mineral. Idiomorphic, tabular zoned pyroxene (size around 1 mm), sometimes with syntaxial over-