80 Y. KIKUCHI 



four at each end. Sometimes they are more numerous at one end, 

 being arranged one upon the other (fig. 5) or, rarely, in rows diverg- 

 ing from the centre (fig. 4). These phenomena indicate the inclu- 

 sion of extraneous matter during the successive growths of crys- 

 tals. A similar kind of symmetrical arrangement of enclosures has been 

 described by E. Cohen* in the Olivine entering into the composition 

 of the lavas of Sandwich Island. 



Sometimes we find very numerous glass enclosures of an elong- 

 ated form running parallel to the direction of the vertical axis, such 

 crystals presenting a hazy appearance in microscopic sections. They 

 are shown magnified on the left hand side of fig. 4. 



Very frequent mineral enclosures are certain small octahedra 

 which are scattered within the crystal with no definite arrangement. 

 They are often in very sharply defined forms, sometimes with their 

 faces depressed in steps, and sometimes in twins, the twinning-plane 

 being an octahedral face. The smaller crystals transmit a dark 

 brownish colour, and are not affected by acids. They are most pro- 

 bably Picotite, an inference also supported by the presence of chromic 

 oxide in the analysis given below. 



The sample for the chemical analysis was obtained from specimens 

 from Tatsumiura by separating with Thoulet's solution. The micros- 

 copic examination of the separated powder showed that there was much 

 glass attached to the crystals. To remove this glass, the sample was 

 lightly treated with hydrofluoric acid. A light green coloured residue 

 was obtained, and the microscope showed that the glass was completely 

 removed, and the smaller crystals came out in a ver) 7 sharply defined 

 form. The crystals were by this treatment scarcely attacked, but when 

 the experiment was tried for a longer time, some of the crystals showed 



* Ueber Laven von Hawaii und einigen andern Inseln des Grossen Oceans, nebsfc einigen 

 Bemerkungen über glasige Gesteine im Allgemeinen. — Neues Jahrb. f. Min. Geol. u. Pal. 

 1880 IT. p. 32 



