366 



I'ltOCEEJUNdS OF THE \ JTIOX.il. MUSK CM. 



cousist's merely of the two i)risins in and I, terminated by the low 



pynimid u. (No. 81259, IT.S.N.M.) 



Fig. 12 belongs to the same type, but has a much richer variety of 

 forms. The prismatic /one includes several forms, 

 among which m \nO\, (J \A50\,X \4.70\,l \120\, (j 

 J I.JO I, aiul h j010| were determined. 



The terminating forms are u |111|, i |223|,/ 

 }021|, and x |243f. The faces of the brachypyr- 

 ainid x are as large as tliose of « and/. 



The second type of crystal is shown in fig. 

 13. The faces of o and y are well developed and 

 narrow faces of the steep pyramid e |441| are 

 l)resent. The o faces are 

 completely devoid of luster, 

 while those of d and y are 

 bright. 



Fig. 14 is a fine clear crys- 

 tal of the same type, hav- 

 ing a small face of/ and the 



pyramid », but no base. 



m 



m 



/^ 



Flu. 14. — TOI'A/- CltYSTAI. 



Viiom .'iiiAZii.. 



SAN LUIS roTOSI. 



m 



m 



V\Q. 15. — TOI'AZ CKYSIAI, 



FROM San Luis To- 

 Tosi, Mexico. 



Several rose and colorless crystals are exhibited 



fioni this locality. They average about 1 cm. in 



breadth and have a steep pyramidal habit similar 

 to the second type of the Bra- 

 zilian crystals. 



Griinhut' describes these 

 crystals, citing several more 

 forms than observed on these particular crystals. 

 The natural etch figures occurring on these crys- 

 tals are arranged perfectly symmetrical with 

 respect to the three symmetry planes of the crys- 

 tal, and while agreeing in the main with the shape 

 of those described by Pelikan,^ they do not show 

 on the brachydome y the right and left unsym- 

 metrical shape of figure which he reports for the 

 etchings on the faces of this dome. 



The most complete combination of forms is seen 

 on the crystal shown in fig. 15. It has the pyra- 

 mids i, u, and o. and also a very narrow e, with the 

 domes </, /, and 7/, the whole truncated by a small 

 Of these the forms c and / are rare for these crystals. The 



m 



m 



Fid. 10.— Topaz cuystai. 

 FiioM San Luis To- 

 To.'<i, Mexico. 



base. 



brachypinacoid is, on the othoi' hand, (luite common. 



U.S.N.M.) 



• Zeit. Kryst. , 1884, IX, p. 124. 



-Tsch. mill. n. petr. Mittli.. ISflO, XI, p. 331. 



(No. 49248, 



