C. Palache and H. E. Merwin — Alamosite. 399 



Art. XXXYI. — Alamosite, a new Lead Silicate from Mexico ; 

 by C. Palache and H. E. Merwin. 



In this paper is presented the description of a monoclinic 

 lead metasilicate showing in form, habit, and composition close 

 analogies with wollastonite, with which it is regarded as isomor- 

 phous. This mineral was sent to the Harvard Mineralogical 

 Laboratory for identification by the Foote Mineral Co. of 

 Philadelphia, who generously placed at our disposal their 

 whole supply of the material. According to their meager 

 data regarding its occurrence it is found in an undeveloped 

 gold and copper prospect situated near Alamos, Sonora, Mexico. 

 The minerals making up the ore in hand are, however, with 

 trifling exceptions all compounds of lead. 



The gangue is in part massive white quartz, in part a com- 

 pact gray, brown or black material shown by analysis to con- 

 tain quartz, the new lead silicate and either limonite or 

 hematite, in varying admixtures. Interspersed through this 

 massive material are occasional F ^ 



vugs lined with quartz crystals ^ ' 



and irregular bunches of the lead Vj ===± ====^ p 

 compounds. Of these the most / v 



abundant is cerussite in snow- / \ ______ 



white aggregates and rare crys- / j 

 tals. Minute flakes of pale green i 



leadhillite were identified by I J- a _ 



cleavage, optical character and 

 chemical reactions. Wulfenite is [_ /__ 

 also found, partly in orange-col- ' ~-^^^^-^^zzzj^g 



orecl crystals, more abundantly as 



a bright yellow stain in all the other minerals, of the ore, par- 

 ticularly in the lead silicate. 



The lead silicate is in radiated fibrous aggregates of more 

 or less pronounced spheroidal form, irregularly interspersed 

 among the minerals already mentioned. It is snow-white in 

 the mass, transparent and colorless in the rare cases where tiny 

 fibers had been free to develop singly in open spaces between 

 the spheroids. There is a perfect cleavage transverse to the 

 fibers yielding a curved concentric fracture surface of pearly 

 luster which extends almost uninterruptedly through all the 

 individuals of a spheroid. The few developed crystals that 

 could be secured for study were minute — not more than 0'5 mm 

 in diameter — and the best of them were but poorly adapted 

 to measurement, several fibers being generally adherent in 

 subparallel groups so that it was difficult to secure readings 



