THE (tREAT ERUrTION OF SAKURA-JIMA IN 1914. 199 



dull Ijroiizy metallic lustre are intergrown with cordierite in 

 approximately parallel arrangemeut in the direction of c-axis 

 (PI. XXII. Fig. 3). 



The brilliantly polarizing simple grains of pure anortliite are 

 partially enclosed or moulded upon dusty cordierite of gray color 

 which is caused by the enclosures of superabundant minute 

 vacuoles. A noteworthy feature is the isotropic colorless fjlass ring 

 which surrounds the grain of anortliite (an) and which intervenes 

 between the latter and the inclosing cordierite xenocryst (PI. XXII. 

 Fig. 2, c), as if the ring were the so-called contact rim.^^ Patches 

 of colorless glass fill up the interstices, which contains air pores in 

 great abundance. In artificial earthenware such partial melts are 

 frequently observed. 



This type corresponds to artificial pottery in regard to its 

 rough granularity although the color is marble-like. It grades into 

 true microtinite, already referred to (p. 190). 



The second type (PL XXII. Fig. 3) — the vesicular lithoidal 

 modification — is a white vesicular body with compact stony ground 

 and external chinks. There are 2 subgroups ; the one with shining 

 flecks of anortliite without visible blue cordierite, the other with 

 abundant blue cordierite spots without plagioclase. 



Microscopically, the highly biréfringent phenocrysts (1 mm.) of 

 simple anorthite are usually found in the more crystalline variety, 

 the cordierite phenocrysts (0.4 mm.) in the finer modification. The 

 cordierite is here composed of heterogeneous, polarizing grains with 

 occasional pleochroic flakes, and the whole is rudely outlined by 

 the homogeneous extinction by which one can discern the mineral 

 from the general ground. Pyrrhotite clumps are enclosed in cor- 



1) The substance of the rim or corona is proljably akin to maskelynite, of the composition 

 of a feldspar in aëroUtes. 



