26 ' ■■ "Vol. XLHL, Art. 5.— T. Katô : 



intimate mixture with grains and prisms of clinozoisite. Chlorite 

 occurs in irregular flakes, representing probably the relics of the 

 original ferromagnesian minerals. This rock may be classed as 

 sadssuriteporphyritü. 



Diabase. A dark green rock, called basalt by local miners, 

 occurs as a dyke with a width of about 2 meters, striking N. 60° 

 W. and cutting across the southeastern part of the Daisen vein. 

 It is compact in texture, but is apt to decompose easily into earthy 

 brittle rock when exposed to the air. It is tine- grained and no 

 phenocrysts are recognizable with the naked eye, though sporadica'ly 

 small amygdaloidal cavities iilled with calcite and zeolite are 

 observed. Under the microscope, it is generally extremely altered 

 as might be expected, although the original intersertal and ophitic 

 structures are but indistinctly preserved (PI. III., Fig. 5). Feldspar 

 is entirely altered to kaolin and shows rectangular and long 

 prismatic outlines, being commonly less than 0.5 mm. in lengtli. 

 Ferromagnesian minerals are all altered to chlorite which occurs 

 ■ abundantly in flaky and filmy forms and fills up the interstices 

 between the lathy feldspar crystals. The chlorite is usually con- 

 taminated with dusty particles of hematitic iron ore. Sparsely, 

 phenocrysts of feldspar entirely replaced by a zeolite or calcite are 

 found. Minute octahedrons of magnetite are abundantly scattered 

 through the rock. Irregular- shaped cavities as well as the interstices 

 between decomposed feldspar and secondary chlorite are filled with 

 a biaxial zeolite, frequently partially replaced by later infiltrated 

 calcite. 



A similar diabase is found in the abandoned adit of Mannenkô 

 as a dyke across the vein. 



