NO. 1148. TOPAZ Cli YSTALS IX THE NA TIONA L MUSEUM— EAKLE. 



363 



Flu. 4.— TOl'AZ CRYSTAt, FROM 



Ilmen Mountains. 



Fig. 4 is a simple combination and seems to belong- to the Admi 

 Clialou type of crystal. No base is present and 

 the brachydome / is proportionately large. 

 Also, the faces of / are broader than those of m. 

 The two remaining forms, u and v? s^re poorly 

 developed. (No. 81255, U.S.N.M.) 



Fig. 5 represents a more general type of these 

 crystals, having the characteristic i)yrauiid ./■ 

 1 243 1 and the additional prism (j ;130^ present 

 as narrow faces. (No. 81253, U.S.N.M.) 



One crystal (fig. (5) is marked by the presence 

 of the brachydome X |023| and the macrodome 

 d 1 201 1, two forms whicli are especially charac- 

 teristic of the Ilmen Mountain crystals. A 



rounded face of q |423| and of // f203| is also present. On the crystal 



represented by the drawing the base is 

 broader than comnion, making .V conse- 

 quently narrow. (No. 81254, U.S.N.M.) 



NERCHINSK DISTRICT. 



The (jrystals from this district are credited 

 to the Aduu CJhalon Mountains and to the 

 Urulga Kiver. Those from the first-named 

 locality are simple in character, and their 

 tyi)0 is shown in fig. 4. The collection em- 

 braces a few single crystals and some large 

 groups. 



Those from the region about the irrulga 

 Kiver are fine, clear, colorless crystals, vary- 

 ing in width from 1 to 4 cm., and quite sym- 

 The combina- 



m 



m 



g. 



Fig. 5. — Topaz crystal kkom Ii. 

 MEN Mountains. 



metrical in appearance 

 tions are mostly simple. Of the prisms 

 m and ?, sometimes one, sometimes the 

 other, predominates, and the same is true 

 of the domes / and y. The macrodome 

 d {201 1 is a characteristic form. The 

 combination seen here (fig. 7) is that of a 

 steep type of crystal very similar to the 

 common type of Mexican crystals. It 

 shows the two prisms, m and /, with o 

 1 221 1 and domes d {201| and y |041(, 

 terminated by a small base, c |001|. 

 (No. 81256, U.S.N.M.) 



Fig. 8 is a s([uare-shaped crystal with 

 broad / faces, distinguished by a great 

 development of the dome / and a long, 

 narrow base. The brachypinacoid h \ 



(!.— TOI-A/. CRYSIAI. FliOM Il.MKN 

 Mol'NTAINS. 



010 1 is also prominent. The 



