6 MISER AND FAIRCHILD: HAUSMANNITE 



tinguishing hausmannite from braunite, though their streaks can 



be used to advantage, hausmannite having a chestnut-brown I 



streak and braunite a dark brownish black streak. 



The optical properties of a specimen of the mineral under ! 



discussion were studied by E. S. Larsen and he concluded that ■ 



it is hausmannite. In fact, he expressed this opinion before i 



the present writers arrived at their conclusion regarding the iden- i 



tification of the mineral and also before the two accompanying 

 analyses (Nos. i and 2) were made. He has kindly furnished 

 the following statement giving the optical properties of the j 



specimen from the Batesville district and for comparison has 

 given unpublished data for a specimen from Piumas County, 

 California : 



"Hausmannite from Batesville district, Arkansas; reddish 

 brown in section and non-pleochroic. Uniaxial — ; col; = 2.45 =*= : 



0.02; €Li = 2.15 ± 0.02. 



"Hausmannite from Plumas County, California; reddish ' 



brown in section and non-pleochroic. Uniaxial — ■; tend to lie 

 on a cleavage normal to the optic axis; o^u = 2.46; ejj = 2.15." 



Penrose'^ gives an analysis of a sample of a mineral from the 

 Batesville district whose description accords rather closely with 

 that of hausmannite, but the composition of the sample whose 

 analysis he gives corresponds to the formula Mn203. He there- 

 fore considered the mineral to be a silica-free braunite and this 

 opinion has been followed by other geologists who have worked 

 in the district, though no further analyses were made until the 

 present investigation was undertaken. For reasons given below • 



the writers believe that the sample for Penrose's analysis con- 

 sisted mainly of hausmannite but contained admixed psilomelane. ' 

 His description of the mineral and the analysis follow: i 



"Braunite. — Specimen from the Sullivan Creek fork of Polk Bayou, 10 

 miles north of Batesville, Independence County. This is a dark ; 



iron-gray or black mineral, forming a coarsely crystalline aggregate 

 with a marked cleavage, the crystal lographic position of the cleavage ' 



being uncertain; lustre submetallic; streak dark chocolate-brown; 

 hardness 5 to 5.5. Its specific gravity, as determined by the chemist 

 of the Survey, is 4.50. '. 



* R. A. F. Penrose, Jr., op. cit, pp. 148-149. : 



