Abstract
The basalts of Hyogo prefecture are composed of many trachybasalts and a few trachyandesites, being accompanied with quartz xenocryst bearing andesite which has genetic relationship with those alkali rocks. They are lava flows which erupted in the age from Pleistocene to Recent. Eight samples of them have been chemically analysed anew. The basalts are characterized with properties that : 1) The rock-type having both plagioclase and olivine phenocrysts is abundant. 2) There is hardly any biotite and zeolite. 3) Basic inclusions are not contained and a few xenocrysts are found. 4) But there is quartz basalt that belongs to the calc-alkali rock series, which is derived from the alkali rock series by the contamination of granitic rocks. 5) They have a chemical tendency to be rich in Al2O2 and CaO and poor in K2O and TiO2. This is occasioned by containing relatively many basic plagioclases.
