372 On ALLANITE, a 



new 



its branches, favoured me with fome fpecimens of this curious 

 mineral, and requefted me to examine its compofition, — a re- 

 queft which I agreed to with pleafure, becaufe I expected to 

 obtain from it a quantity of yttria, an earth which I had been 

 long anxious to examine, but had not been able to procure a 

 fufficient quantity of the Swedifh Gadolinite for my purpole. 

 The object of this paper, is to communicate the refult of my 

 experiments to the Royal Society, — experiments which cannot 

 appear with fuch propriety any where as in their Tranfac- 

 tions, as they already contain a paper by Mr Allan on the mi- 

 neral in queltion. 



I. Description. 



I am fortunately enabled to give a fuller and more accurate 

 defcription of this mineral than that which formerly appeared, 

 Mr Allan having, fince th,at time, difcovered an additional 

 quantity of it, among which, he not only found freftier and 

 better chara&erifed fragments, but alfo fome entire cryflals. In 

 its compofition, it approaches molt nearly to Cerite, but it dif- 

 fers from it fo much in its external characters, that it mufl be 

 confidered as a diftinct fpecies. I have therefore taken the li- 

 berty to give it the name of Allanite, in honour of Mr Allan, 

 to whom we are in reality indebted for the difcovery of its pe- 

 culiar nature. 



Allanite occurs maffive and difTeminated, in irregular 

 mafTes, mixed with black mica and felfpar; alfo cryftallifed ; 

 the varieties obferved are, 



i. A four-flded oblique piifm, meafuring 117 and 63 . 

 2. A fix-fided prifm, acuminated with pyramids of four fides, 

 fet on the two adjoining oppofite planes. Thefe laft are 

 fo minute as to be incapable of meafurement. But, as 

 nearly as the eye can determine, the form refembles 

 Fig. 1. ; the prifm of which has two right angles,, and 

 four meafuring 135 . 



3- A 



