No. 2395. LVDWIGITES FROM IDAHO AND KOREA— SHANNON. 671 



diopside. Koto 5 concludes that the ludwigite was first deposited, 

 followed by the diopside, after which the deposition of the sulphides 

 and recrystallization of the calcite took place. 



Physical properties. — The ludwigite is entirely black in color in the 

 hand specimen and consists of radiating or divergent aggregates of 

 prismatic fibers. The luster is silky. The hardness is about 5.2-5.5. 

 The streak is greenish to brownish-black and is distinctly darker than 

 that of the Idaho ludwigite. A peculiar property of this ludwigite is 

 its magnetism. When powdered to 60 mesh all of the particles can 

 be picked up with a common horseshoe magnet. When powdered 

 very finely and examined under the microscope no magnetite inclu- 

 sions were found in the mineral and no magnetite was visible on 

 polished surfaces, so that the magnetic property must belong to the 

 borate itself. This is further discussed below. 



Optical properties. — Under the microscope very thin needles are 

 transparent, but are very deeply colored, distinctly more so than the 

 Idaho material described above. They are markedly pleochroic, the 

 color parallel to the elongation being brown and that perpendicular 

 to it green, the absorption being greatest in the former direction. 

 Owing to the deep color of the mineral the birefringence is greatly 

 obscured and the optical character could not be determined. The 

 indices of refraction are higher than the range of immersion media 

 at hand. 



Pyrognostics and chemical properties. — The mineral yields water 

 (extraneous) in the closed tube. It is slowly soluble in hydrochloric, 

 nitric, and sulphuric acids, and gives the usual reactions for boron 

 and iron. 



Chemical composition. — The ludwigite was separated from the 

 accompanying gangue material by the use of heavy solutions. The 

 relatively pure material thus obtained was analyzed with the follow- 

 ing results: 



Analysis of ludwigite from Korea. 



Silica (SiOi) 0. 40 



Ferric oxide (Fe 5 3 ) 32.49 



Alumina (ALOs) 2. 32 



Boric anhydride (BsOa) 16. 80 



Ferrous oxide (FeO) 10. 40 



Lime(CaO) 1.86 



Manganous oxide (MnO) 36 



Magnesia (MgO) 34. 54 



Water (H*0) above 110° C 1.42 



Total 100. 59 



Of the above constituents the silica, water, and lime are quite 

 probably extraneous, the silica and lime being doubtless derived 



» Koto, Journ. Coll. Sci. Tokyo, 1910, p. 23. 



