a New Mineral Species. 275 



to 170. The angle of 159 2' corresponds to the pyramid 



(P 1)*, exactly the same ratio as we find in the two forms 



of pyramidal Tin-ore, noted * and z by HAUY. The angle of 

 169 26' belongs to (P + I) 5 . There is no sharp edge between 

 these faces ; but wherever they are most distinctly pronoun- 

 ced, they seem rather to approach to the position of the first of 

 these pyramids. The acute four-sided pyramid z is often in 

 combination only with P GO , as in Fig. 5. 



No crystal has yet been observed terminated on both ends. 

 In the portion of one represented in Fig. 4., the faces of the four- 

 sided pyramid z are disposed in the opposite direction from that 

 in Fig. 3. This may be conceived to be the opposite apex of 

 the crystalline forms. 



There are faint traces of a cleavage observable parallel to P, 

 the fundamental pyramid of the species ; but they are incoherent, 

 and much interrupted by conchoidal fracture, which is of a high 

 degree of perfection. The surface of all the forms is rather un- 

 even, often irregularly streaked and rough. 



Fergusonite possesses an imperfect metallic lustre, inclining 

 to vitreous in the perfect conchoidal fracture. Its colour is dark 

 brownish-black ; but, in very thin scales, it appears of a pale li- 

 ver-brown or yellowish-brown colour, and is translucent ; in lar- 

 ger crystals it becomes opake. Its streak is a pale brown pow- 

 der, exactly the same as in peritomous Titanium-ore. 



It is brittle, the hardness rr 5. 5... 6.0, nearer the latter ; it is 

 scarcely different from that of the prismatic Feldspar. The 

 specific gravity, taken with great care by Dr TURNER, was found 

 5.800, nearly agreeing with 5.838, the result obtained by Mr 

 ALLAN. It does not act upon the magnetic needle. 



Both these species were discovered in Greenland by Sir 

 CHARLES GIESECKE'. Allanite occurs at Alluk near the south- 



