406 D. A. MacAUster — Cassiterite and 8pecular Iron 



not ascertain, but, on the assumption that it is 2 per cent., the 

 amount of specular iron present must, at the lowest computation, 

 be "Well over 8 per cent., since for every ton of dressed Black-tin 

 obtained nearly 4 tons of specular iron have been removed by 

 a magnetic separator, and a still greater amount has been washed off 

 in the processes the material subsequently undergoes. It would be 

 safe to say that the lode contains about 20 per cent, of iron-ore. 



The employment of the magnetic separator is merely to free the 

 tinstone from the iron-ore, and, with the exception of 25 tons of 

 specular iron-ore containing 5 8 '8 per cent, of iron, which were sold in 

 1906 at the rate of £2 a ton, the ferruginous by-product has proved 

 so far useless, since it is a variety too hard to be readily ground to 

 a pigment and not quite suitable for the smelter, even if enough 

 could be obtained. 



Fig. 3. Microphotograph of Specular Iron-Tinstone from Birch Tor. 

 Q, quartz, all of one generation, in which the other minerals are 

 set ; C, cassiterite ; S, specular iron ; T, tourmaline ; M, fine mica. 



Other occurrences of specular iron in the neighbourhood and 

 elsewhere will now be referred to so as to compare them with that 

 of Birch Tor. 



The neighbourhood of Lustleigh, which lies to the east, has long 

 been known as a producer of micaceous or ' shining ' ore, and De la 

 Beche states that among its uses this mineral was formerly employed 

 under the name of ' Devonshire Sand ', which was sold at the rate of 

 from £3 3s. to £8 8s. a ton as a writing sand. As it is a soft variety 

 of specular iron it has in recent times been used chiefly as a pigment, 

 but a little has also been smelted. 



In a paper read in 1895 ^ Mr. Joseph S. Martin described the nature 



1 J. S. Martin, "Micaceous Iron Ore near Bovey Tracey " : Trans. Manchester 

 Geol. Soc, 1895, vol. xxiii, p. 162. 



