X, A, 1 Smith, Edding field, Fanning: Philippine Minerals 93 



It occurs in botryoidal or massive shapes; also, reniform. It is 

 found as veinlets in andesite and as nodules from erosion of 

 veins and possibly in beds. It is found in Ilocos Norte, Panga- 

 sinan, Bulacan, Tarlac, and Masbate. It is not exploited. 



Pyroxene — Ca(Mg, Fe)Si206. 



Pyroxene is a common constituent of pyroxene andesite, one of 

 the chief rock types in the Islands. It occurs in small jet-black 

 crystals. It has no economic value. 



Quartz — SiOj. 



Quartz is very persistent under conditions from deep seated 

 to surface. It occurs in fine crystals in vugs under proper con- 

 ditions; otherwise, it generally takes the form of jasper, chert, 

 or siliceous sinter at the surface. It occurs in veins and as 

 silicification of wall rocks. Two workable deposits only are 

 known; (1) Siliceous spring deposits, Baguio, and (2) beach 

 sand, Looc, Lubang Island. Quartz is used locally for road ma- 

 terial and concrete in Baguio and at Looc. 



Realgar — AsS. 



Realgar occurs as characteristic red crystals on a yellow coat- 

 ing of orpiment on pieces of slag (?) from the old Santa Bar- 

 bara furnace at Mancayan, Luzon. As far as we know it does 

 not occur in a natural state in the Philippines. Specimens, No. 

 59, of realgar are in the museum of the Ateneo de Manila. 



Rhodochrosite — MnCOg. 



Rhodochrosite occurs as a gangue mineral in auriferous cal- 

 cite veins of Benguet. It is a primary mineral ; it was probably 

 leached from wall rocks by the ascending solutions and was later 

 deposited with the calcite. Rhodochrosite is of no economic use. 



Rutile— TiOs. 



Microscopic crystals occur in some of the metamorphic rocks 

 from Ilocos Norte associated with actinolite, muscovite, etc. 

 Rutile has no economic value. 



Salt— NaCl. 



Salt is deposited as incrustation from brackish carbonated 

 springs in Mountain Province, Luzon, notably at Asin. It is 

 used by the Igorots. 



Sanidine — (K, Na)AlSi308. 



Sanidine occurs in small crystals and grains. This "glassy 

 feldspar" is a dominant constituent of the andesites of many 



