Rogers — Lorandite from the Rambler Mine, Wyoming. 105 



Art. XIV. — Lorandite from the Rambler Mine, Wyoming ; 

 by Austin F. Rogers. 



I am indebted to Mr. Berger, of Placerville, California, for 

 an interesting specimen from the Rambler mine, near Encamp- 

 ment, in southern Wyoming. This specimen consists of dark 

 fine-grained massive pyrite, upon which are implanted barite 

 crystals and well-formed crystals of orpiment. With the orpi- 

 ment and barite are associated several orange-red realgar crys- 

 tals and a single deep red crystal of what proved to be 

 lorandite or thallium metasulfarsenite, TlAsS 2 . This is the 



second known occurrence of lorandite, the original locality 

 being Allchar in Macedonia.* 



The crystal mentioned is an imperfect one, of about 4 mm 

 size, bounded by the faces of a rhombic prism with interfacial 

 angles of about 90° (calc, 93°) and by three cleavages in one 

 zone, which is at right angles to the prism zone. Using 

 Gold Schmidt's orientation, f the prism faces constitute the 

 {110} form _and the three cleavages are parallel to {100}, 

 ] 001 1 , and {101}. The accompanying figure (plan and side 

 elevation) gives an idea of the crystal. All the faces but 

 {110} are cleavages. The following angles measured on the 

 reflection goniometer prove that the crystal is lorandite. The 

 first mentioned angle was measured on a detached fragment, 



Measured Calculated 



100(clv.) :001(elv.)= 52°49' 52°2'7' 



001(clv.) : 101 (civ.) = 51°17' 51°49' 



while the other angle was measured by mounting the matrix 

 specimen on the goniometer, as it was feared that the crystal 

 would go to pieces if detached from its matrix. The cleavage 

 parallel to {100} is very perfect, that parallel to {001} good, 

 and that parallel to {101} fair. The luster is adamantine on 



*Krenner, abstract in Zeitsehr. Kryst. Min., vol. xxvii, p. 98, 1897. 

 fZeitschr. Kryst. Min., vol. xxx, pp. 272-294, 1899. 



Am. Jour. Sci.— Fourth Series, Vol. XXXIII, No. 194.— February, 1912. 



