On Columbite. 15) 
nexed description of the crystal according to Naumann’s system of 
notation: 
OP .ipe.P.63.266.2Ra. 
P é a. af. - Of é 
ePac.cP2.acP.cB3.aPa. 
M é é Mi 
A comparison of the above angles, Jeaves no doubt that this erys- 
tal is a specimen of the species Columbite: and we may extend this 
remark to all the specimens from the same locality ; for perfect erys- 
tals, affording the same angles, are of frequent occurrence, The 
crystal figured by Dr. Thomson is so very irregular, that it cannot 
be considered an exception to this remark. It presents but one re- 
placed lateral edge, and one replaced angle, which sufficiently indi- 
cate that little or no reliance can be placed upon its apparent form. 
According to Dr. Thomson’s measurement, M : T (mean of 5 tri- 
als)=84° 20’, T : e (plane replacing the acute lateral edge)=152°, 
M : e=110° 20’, a: ¢ (inclination of the plane on the angle, to the 
adjacent lateral edge) =143° 45’. The last inclination nearly coin- 
cides with the interfacial angle a ; e as above given. This close ap- 
proximation would authorize a suspicion of the identity of the crystal 
examined by Dr. Thomson, with the more regular and highly finished 
individuals so frequently afforded by the locality. The crystals from 
Middletown, though often minute, occur occasionally of a gigantic 
size. Prof. Johnston, of the Wesleyan University, has lately de- 
scribed a fractured crystal which originally weighed 14 lbs.* His 
description is accompanied with a figure of the larger fragment into 
which it was broken. Its weight was 6 Ibs. 12 oz. avoirdupois, and 
in length and breadth it exceeded seven inches. Its general form 
was similar to the above figures, and it presented the faces M, M, e, 
é, @, &, and another imperfect plane, which appears to be 0/ 
From the identity in the crystallization, therefore, of the “Mi ddle- 
town and Bodenmais specimens, we are compelled to assent to their 
continued union in the same species. Slight discrepancies in the 
physical characters, if they actually exist, should not influence the 
* See this Journal, Ae The Columbite at Middletown irregularly 
disseminated in a coarse grani i ica and feldspar in | Ni 
masses. This feldspar has moi quarried for the manufacture of act and 
by this means the fine specimens of Columbite which the locality has afforded, 
Albite and small quantities of uranite, rutile and apatite are 
have be 
weed with the Colambite. 
