122 



bad escaped my attention owing to their small number and 

 diminutive dimensions 



Tbus tbere already existed in the Lützen collection nep- 

 tunite crystals of two different types. Amougst the material 

 collected by me at the locality another type has been found, 

 so that at present three distinct types at least are known. 

 Between these types there do not, as is otherwise often the 

 case with differently developed crystals of the same mineral, 

 exist any intermediate forms; on the contrary, the neptunite 

 crystals form sharply defined groups, the representatives of 

 which have been found at separate places and in different 

 associations. A description of each type is given below. 



Type I. 



Here belong the neptunite crystals previously described by 

 the author. They occurred in the Lützen collection in tolerably 

 large numbers, and some of the single individuals were rather 

 large. The largest individual that has been found, is a twin 

 crystal measuring 5'='" in length and 4^=°^ in thickness. In 

 general habit the crystals belonging here bear some resemblance 

 to octahedrons (Fig. 6, Plate VI). They are bounded by the 

 following forms: 



a={lOO}, è = {OlO}, c = {00l}, m = {no}, d = [Ъ0\}, 

 e = {201}, s = {in}, V = {221}, и = {M2}, о = {ni}. 



Twin crystals occur, but are very rare; 1 have not seen 

 more than three. They are formed with the third pinacoid as 

 twinning plane and one individual revolved 180° with reference 

 to the other. 



It is most probable that the whole supply of neptunite in 

 the Lützen collection had been found at one and the same 

 place on Narsarsuk, namely at the locality No. 4. I could not, 

 at least, find any trace of neptunite of this type at any other 

 locality. The mineral occurred here only as isolated crystals 



