368 J. L. Smitfi — Examination of American Minerals. 



quarries of Eockport, but its nature had not been determined. 

 The quantity theu found was very small and only a portion of 

 it was given to me; a short time afterward, I informed Mr. 

 Knowlton that it was fergusonite, and requested him to look 

 further for specimens. Since then but little more has been 

 found, but enough was furnished me to make out its true char- 

 acter, both physically and chemically, except its ci 

 form. It is found particularly at one locality near the intersec- 

 tion of two trap dykes. 



For a space covering about thirty or forty feet, masses of 

 feldspar and quartz replace the granite, and it is in the feldspar 

 that the Fergusonite is found, intimately associated with cyrto- 

 lite, and sometimes even penetrating crystals of this last mine- 

 ral. In the same feldspar, annite, cryophyllite, and fine crys- 

 tals of smoky quartz are found. 



The mineral is of a fine dark brown color in the interior, with a 

 clear conchoidal fracture ; resinous luster ;* hardness 6 ; specific 

 gravity 5'681 ; streak light brown; powder, ash-colored; but 

 when heated to a bright red heat for fifteen minutes changing 

 to a light greenish yellow color with a loss of 1/50 per cent. 



Oolumbic acid 48*75 



Yttria ..46-01 



Cerium oxides 423 



Water (loss by heat) 1*65 



sonite from Greenlai 

 Remarks as to the chemical character of the minerals described. 

 The compositions of the columbates from the various locali- 

 ties appear at first sight to be very complex and irreg 



-. and due allowance be made for the inter- 

 mixture of these minerals, winch intermixture cannot be 

 detected on account of the similarity of color and fracture ot 

 nt minerals, this irregularity disappears to a greater 



The first, and the one best known, cohimbite, is well recog- 

 nized as a simple columbate of iron and manganese. 



Microlite, from what little we know of its eoi 

 appears to be a columbate of lime. Pyrochlore is to be regarded 



* The action of a red heat on small fragments is to change their color to a 

 greenish yellow ; but before this takes place, the fragments exhibit the phenome- 

 non of glowing in a manner more striking than any specimens of gadohmte, a 

 mineral remarkable for its glowing, that 1 have experimented with. From lack oi 

 material I did not take the specific gravity after heating. 



