53 



STUDIES FOR STUDENTS 



Fig. 2. 



Fig. 3. 



are called, after Alois von Widmanstatten, who first produced 

 them in the year 1808 by heating a section of the Agram 

 meteorite, Widmanstatten figures. The production of these 

 fio-ures is evidence that the meteorites on which they occur 

 (1) have a well-defined crystalline structure and (2) are not 

 homogeneous in composition. Evidence of crystalline struc- 

 ture is not confined 

 to results obtained 

 by etching : many 

 meteorites show in 

 their natural condi- 

 tion a structure of 

 plates intersecting 

 at definite angles. 

 Study of the angles 

 at which the bands 

 meet both in etched 

 and natural speci- 

 mens shows that the 

 crystallization of 

 most iron meteorites 

 is octahedral, i. e., 

 they are formed of 

 plates or lamellae 

 arranged parallel to 

 the four pairs of faces 

 of the octahedron. 

 Though this arrangement may for practical purposes be con- 

 sidered a simple one, it is really according to Linck the result of 

 a polysynthetic twinning. The angles at which the bands inter- 

 sect in any given section depend wholly on the direction of the 

 section, as the accompanying figures will show. If the section 

 is parallel to an octahedral face it will show three systems of 

 bands intersecting at angles of 6o° (Fig. 2). If the section is 

 parallel to the face of a cube there will be two systems of bands 

 intersecting at angles of 90 (Fig. 3). If the section is parallel 



Fig. 4 



Fig. 5. 



