'SG2 



PROCEEDINGS OF THE XATIOXAL MUSEUM. 



I 



m 



m 



I 



Fig. 1.— Toi'a/, ckystal 



FROM ALAHASIIKA. 



essentially of the three predominating forms |120|, |001|, and f041( 

 in combination al<me, or with narrow faces of 

 some of the other (!ommon forms; a rarer and more 

 complex type, in which the unit prism {110| has 

 a greater development than the prism |120|, and 

 whose combinations are much richer in the vari 

 ety of forms. This second type is not well rep- 

 resented in the lot, as it is seldom that the unit 

 prism is as large as the other prism \ 120 1, besides 

 tlie combinations are all quite simple. 



While the general habit is the same for all 

 these crystals, the combinations are quite varied. 

 I^Mg. 1 represents tlie simplest and most common 

 type of the crystals. The prism / |120|, base c 

 ;001|, and dome y |041| are largely developed, 

 while tlie prism m |110| and pyramid i \22'.\\ are 



shown more as beveling planes. Usually one face of y is much larger 



than the other, and occasionally u \1\1\ is also 



present. (No.' 81247, [T.S.N.M.) 



On a crystal (Hg. 2) there are, besides the 



forms ?, c, y, m, and i, cited above, two addi- 

 tional pyramids, w I 111 I and 1 221 1, and the 



dome/S021|. The form o is not prominent 



on any of the crystals, nor does it appear of 



frequent occurrence. The brachydome /" is 



rare and its faces usually narrow. 

 The drawing (lig. 3) represents the general 



appearance of a crystal. In addition to the 



forms I, c, y, m, ?, and v, the very narrow raac- 



rodome h |023| 'truncates the edges of i, and 



the brachypinacoid /> |010{ is i)resent. These 



last two forms are of very rare occurrence on the Alabashka crystals. 



(No. 81244, U.S.N.M.) 



ILMEN MOUNTAINS. 



Crystals of topaz from the Miask district 

 are noted for their great variety of combina- 

 tions and many rare forms, and those of the 

 collection, although lacking numy of these 

 rarer forms, yet have much richer and notice- 

 ably different combinations from those of the 

 Alabashka crystals. From these latter they 

 have several distinctive characteristics; they 

 are mostly colorless, the base is generally 

 small and sometimes absent, the two bracliy- 



domes/ )021,* and X \023\ are common and the faces of the unit prism 



wt are often broader than those of 1. 



FlO. 2.— TOPAZCRVSTAI. KKOM 

 ALAltASllKA. 



Fig. 3. 



-Topaz ruYSTAi. fkom 



Al.AHASIlKA. 



