94 27i<; Philippine Journal of Science itw 



peaks in Zambales Mountains and of Mount Apo, Mindanao. It 

 is of no economic value. 



Sardonyx — SiO... 



A specimen of this, No. 174, from Baganga, Mindanao, is in 

 the collection of the Ateneo de Manila. 



Sericite— 3Al,0,.6SiO,.2H,,0. 



Sericite is one of the micas occurring in the schists of Ilocos 

 Norte and Zamboanga Peninsula, Mindanao. It occurs in small 

 gray-blue silky flakes. It is of no economic use. 



Serpentine — H, (Mg, Fe) ,SioO,. 



Serpentine, associated with pyroxenites and peridotites in 

 more or less stinictureless masses, is found in Ilocos Norte 

 and other localities. It is a greenish mineral. It occurs usu- 

 ally as asbestiform minerals. There is no production in the 

 Philippines. 



Silvanite — ( AuAg) Te„. 



Silvanite occurs intimately mixed with the lead telluride al- 

 taite in quartz and calcite stringers in a contact between a slaty 

 formation and a feldspar-porphyry dike. 



Silver — Ag (metallic). 



Silver occurs in the Philippines only in natural alloys with 

 gold, and associated with the mineral galena. The gold from 

 both placers and lodes in the Philippines carries silver varying 

 in quantity up to 30 per cent. Silver-bearing galena is found 

 at Panopoy, Cebu, and near Paracale, Camarines. 



Sphalerite — ZnS. 



Sphalerite occurs massive or as small crystals, always asso- 

 ciated with lead and pyrite. Like the other sulphides, it favors 

 the quartz veins; it fonns under conditions of moderate depth. 

 It is found in practically all localities where galena is found 

 (see Galena). Sphalerite is not found in economically valuable 

 quantities in the Philippines, although widely found in many 

 veins. It is not utilized. 



Stibnite — Sb^Sa. 



Stibnite occurs in characteristic fibrous masses. There is 

 only one specimen in the Bureau of Science collection from Ba- 

 tangas Province, Luzon. 



