88 "^^^ Philippine Journal of Science isis 



Guano — PjOj with impurities. 



Guano occurs as a coarse brownish earth in limestone caves 

 in many pai-ts of the Archipelago, principally along sea coasts. 

 A small amount is collected, which is sold to Japanese exporters. 



Gypstun — CaSO^. 



Gypsum occurs generally in small tubular crystals as incrusta- 

 tions on volcanic rocks near solfataras; also, in finely granular 

 form in the Loboo Mountains, Batangas, Luzon. There is no 

 production, and the quantity is apparently limited. 



Hematite — Fefi^. 



Hematite is found in irregular "pockets" with magnetite, 

 pyrite, chalcopyrite, and quartz in crystalline rocks of the East- 

 ern Cordillera of Luzon; also, in veins cutting limestone. It 

 occurs from Mambulao Bay, Ambos Camarines, to northern 

 Bulacan, Luzon. The grade of this ore is excellent. It is 

 smelted by Filipinos in crude blast furnaces to make plowshares. 



Hornblende — RSiOg, R being more than one of the elements Ca, 

 Mg, Fe, Al, Na, and K. 

 Hornblende is abundant in many igneous rocks as black crys- 

 tals varying in size from microscopic to 2 or 3 centimeters in 

 length. It is of no economic value. 



Hypersthene — (FeMg) SiOj. 



Hypersthene occurs in certain varieties of andesite in many 

 localities. It is distinguished by its pleochroism (colorless to 

 delicate pink) under the microscope. Hypersthene has no eco- 

 nomic value. 



Iddingsite — Exact composition not known. 



Iddingsite occurs as alteration of olivine in rocks from three 

 localities, Mount Mariveles, Bataan ; Mindoro ; and Batanes. The 

 mineral is red. It has no economic value. 



Ihnenite— (Mg, Fe) TiOj. 



Ilmenite is found in black-sand concentrates in many streams 

 throughout the Archipelago, usually in small crystals and more 

 or less rounded grains. It is not utilized. 



Iridium — Ir (metallic). 



The occurrence of iridium is the same as osmium. 



Jasper — SiO,. 



Jasper occurs in fissile beds and in irregular masses. It con- 

 tains remains of radiolarian tests. The color is browTi to deep 

 red. 



