14 - ART. 12. — B. KOTO : 



Accessory: Magnetite, titanite, allanitc, 

 zircon, apatite, iron-pyritc. 

 Macrotexture : Porphyroid. 

 This light rose-colored, alkalic granite has a coarse, incquigranular, 

 skcdo-porphyritic fabric. The flesh-colored megaphcnocryst of ortho- 

 clase is flat-prismatic, 2 C7n in length, carlsbad-twinncd, and partially 

 decomposed. It is optically normal, and encloses zircon, apatite and 

 patches of anorthoclcn^e (?) (extinction, 3° 40' to M), tlic last is oriented 

 parallel to (010) of orthoclase. Prismatic green hornblende (3 onm in 

 length) is fibrillated, and occnrs associated with idiomorphic, nearly 

 nniaxial biotite and hypidiomorphic magnetite (1 mjn). The biotite 

 contains an octagonal, highly double refractive, colorless basal section 

 of zircon or cassiterite with pleochroic halo, and bleaches green. The 

 oligoclase is hypidiomorphic Math zonal and reticulated lamellar struc- 

 tures, extinguishing light symmetrically from 4° to 5°. The relation 

 of dull orthoclase and quartz is eutectic ^^; the former is idiomorphic 

 with reference to the latter. The xenomorphic, highly pleochroic allanite 

 is rather abundant ; the hypidiomorphic apatite and zircon, and the 

 xenomorphic titanite are present in small quantities. The idiomorphic 

 irou-pyrite occurs enclosed both in orthoclase and quartz, showing that 

 the sulphidic ore is not formed secondarily during the post-volcanic 

 period, nor by the circulation of underground waters. The order of 

 crystallization is zircon, apatite, allanite, titanite, phcnocrystic ortho- 

 clase and oligoclase, magnetite, biotite, hornblende(!), irou-pyrite, quartz, 

 and lastly, xenomorphic orthoclase. Tlie rock shows no signs of cata- 

 clastic structure, which is a feature rarely missing in Korean granites. 

 Locality : Peripheral portion of the granitic stock of ün~jin-san. 



1) In a specimen ut the contact with the contact-metamorpliosed limestone, the quartz 

 })lays another rôle with re.spect to a dirty orthoclate. Here the quartz has rounded edges, 

 sometimes with embayments, :md the substance of the quartz is also fritted and fractured 

 yV\. III. fig. 4); in short, it shows evidently many signs of magmatic corrosion, indicating 

 at the same time that time has elapsed between the formations of the quartz and tiie in- 

 iilling ortlioclase. ïhib state of aggregation of components is characteristic of porphyritic 

 eruptives. 



