■12 Trof. Maskclync and Dr. Lang's Miner 'alogical Notes. 



p. 445). Professor Miller's indices are convertible into those of 

 Schrauf by dividing the x and z indices in his treatise by 3. 



Its specific gravity is high, coming near to, but being rather 

 higher than that of the variety of the Ilmen Columbite, de- 

 scribed by Hermann as possessing the highest specific gravity. 

 He places this limit at 5*73. In other respects, too, the Monte 

 Video Columbite exhibits a remarkable analogy with the Colum- 

 bite of Ilmen. 



Schrauf has figured (fig. 6 of his memoir) a crystal from the 

 Ilmen Mountains, and in fig. 4 one from Haddam, both presenting 

 much similarity to this crystal. They belong to the crystalline 

 type which he has called " Habitus I. •" and it is this l< habit M 

 which the Monte Video crystal affects. There is, however, also 

 a crystal of the Ilmen Mountain Columbite numbered 8 among 

 the specimens acquired with the Allan-Greg collection by the 

 British Museum. 



It is a very perfect little crystal, and presents a near resem- 

 blance to that found by Mr. Lettsom. But its specific gravity 

 is 5*969, a much higher one than even the highest assigned 

 by Hermann to the Columbite from the Siberian locality, and in 

 fact is that of some specimens from Bodenmais. But what 

 gives an important interest to this specimen, is the circumstance 

 that it carries a plane identical with a new plane on the Monte 

 Video crystal, viz. (15 0). 



The forms it exhibits are identical with those carried by the. 

 Monte Video crystal, with the exception that the plane n is 

 absent (see fig. 4). 



A locality producing Columbite is almost sure to prove one of 

 much mineralogical interest when investigated. The analogy of 

 the Monte Video specimen to those from the Ilmen Mountains 

 may fairly justify the hope that so skilled a mineralogist as Mr. 

 Lettsom may yet bring to light other interesting minerals from 

 the Monte Video locality. 



The existence of the plane (1 5 0) is established by the follow- 

 ing angles, each of which is the mean of three measurements on 

 various parts of the crystal : — 



Allan Greg, No. 8. Monte Video. Calculated. 



(010) (150) = 26 23 26 20 26 9 



(13 0) (15 0) = 13 8 13 18 13 8 



There can be no doubt about the indices of this plane, as the 

 corresponding angles for the plane (1 6 0) are 



(010) (16 0) = 22° 15' and (13 0) (160) = 17° 2'. 



