PHYSIOGRAPHY. 195 



Specular Iron. 



Cleavage, parallel with P and o. In some varieties 

 scarcely any traces appear, while in others it seems to be 

 perfect, which however, must in a great measure be attrib- 

 uted to composition. Fracture conchoidal, uneven. Sur- 

 face, s is horizontally streaked, sometimes so deeply that it 

 appears rounded ; P is sometimes streaked parallel to the 

 edges of combination with n; y is uneven, and often curved. 



Lustre metallic. Color dark steel-grey, iron-black. 

 Streak cherry-red, reddish brown. Surface frequently 

 tarnished ; generally with the exception of o, which may 

 be useful in finding the true position of the crystals, when 

 they become complicated. Opake ; very thin laminae are 

 faintly translucent, and show a deep blood red color. 



Brittle. Sometimes feeble action upon the magnetic 

 needle. Hardness = 5*5 . . . 6*5. Sp. gr. = 5*251, a crys- 

 talline variety from Sweden. 



Compound Varieties. Twin-crystals. 1. Axis of rev- 

 olution perpendicular; face of composition parallel to o ; 

 the individuals are continued beyond the face of composi- 

 tion. (Altenberg, Saxony.) Sometimes two individuals in 

 ^the same position are joined in a face of w, and terminate at 

 this face. (Stromboli.) 2. Axis of revolution perpendicu- 

 lar, face of composition parallel to a face of P. 



Globular, reniform, botryoidal, and stalactitic shapes : 

 surface generally smooth, composition more or less thin co- 

 lumnar, sometimes even, impalpable ; in this case the lustre 

 becomes imperfectly metallic, and the color red ; fracture 

 of impalpable compound varieties, even, flat conchoidal, or 

 uneven. Compound varieties often join in a second and 

 third composition, which are curved lamellar and granular; 

 the junction of granular masses produces frequently very 



