'236 Goldschmidt and Parsons — Notes on Goethite. 



face or " Scheinflaeche," and it gives a bright band of light in 

 the prism zone with the angle $ varying from 3° to 20°. In 

 this band are bright points which imperfectly indicate the 

 positions of the faces oo 3(130), oo 4(140), oo 5 (150), oo 6 (160), 

 oo (180), oo 12(1 , 12 , 0). The harmonic discussion of the char- 

 acteristic indices in this series gives oo 3, oo 4, oo 6, and oo 8 as 

 the points of best position, but no characteristic letter is assigned 

 to them until they have been determined by single distinct 

 reflecting faces. The symbol XX is used for the series and in 

 figure 2, oo 4 represents the series. 



For comparative purposes three crystals from Lostwithiel, 

 Cornwall, were measured and the habit and faces are shown in 

 figure 1. The observed forms are b ~ Ooo (010) ; M = 2oo 

 (210); ^=Aoo(430); y = oo (110) ; Z = oo2(120); ^ = 10(101); 

 e = 01 (011) ;p = 1 (111) ; w = -fi (413). All the forms except 

 x were present on every crystal. The new form x —- foo (430) 

 was present on two crystals and for the best reflections gave 

 angle 4> 55° <V and 55° 33'. A poor reflection gave one face as 

 57° 27 ; . Angle p was in every case 90°. The calculated 

 angles are <fc 55° 26 ; , p = 90°. The face is small but well 

 defined, and may be regarded as well established. The form 

 w — J-J-(413Hs also new and is present on all three crystals 

 with four faces on each. The faces reflect well and give a dis- 

 tinct signal cross, but it is worthy of remark that the reflection 

 is slightly yellow while the others are white. The angles 

 agree well among themselves, but in every case the angle p is 

 20' to 69 ; less than the calculated angle. The calculated 

 angles are <$> = 77° 4 7 , p 42° 6 ; . Considering the good character 

 of the reflection and the sharpness of the faces, this difference 

 is not easily understood, but the form may be considered as 

 well established. 



Heidelberg, Aug. 14, 1909. 



