ORDER vui. PERITOMOUS TITANIUM-ORE. 377 



Fundamental form. Isosceles four-sided pyramid. 

 P = 117 2', 95 13'. Vol. I. Fig. 8. HAUY. 



a = Vl-2- 

 Simple forms. P 1 = 128 41', 67 58' ; P (c) ; 



P + QD (/); [P + oo] (J/); (P + oc) 3 (h) 



= 126 5% 12", 143 7 48". 

 Char, of Comb. Pyramidal. 

 Combinations. 1. P. (P -f x) 3 . Orisons. 



2. P. P + oo. [P + ooj. Sim. Fig. 101. Teinach, 

 Stiria. 



3. P 1. P. P + QD. [P -F oo]. Sim. Fig. 

 101. Saualpe, Carinthia. 



Cleavage, P + oo and [P -f oc], perfect, but very 

 much interrupted. Fracture conchoidal, uneven. 

 Surface, P and P 1, either smooth or rough, 

 but both of the same physical quality : the prisms 

 vertically streaked. 



Lustre metallic adamantine. Colour reddish-brown, 

 passing into red, sometimes yellowish. Streak 

 very pale brown. Translucent ... opake, some- 

 times in a strong light transparent. 



Hardness = 6-0 ... 6-5. Sp. Gr. = 4 249, the 

 dark coloured variety from Ohlapian. 



Compound Varieties. Twin crystals very fre- 

 quent, axis of revolution perpendicular, face of 

 composition parallel to a face of P 1. The 

 composition produces geniculated groupes, and is 

 often repeated in several geniculations. Thin and 

 long individuals produce after this law a reticu- 

 lated composition. Massive : composition granular, 



