168 IDDINGS. 



Metadiorite, which appears to be metamorphosed gabbro, is of frequent 

 occurrence. 



That from Malitbog, Leyte, is medium-grained, inequigranular and consertal, 

 and consists of labradorite, without zonal structure, and green hornblende, both 

 compact and fibrous. 



Another metadiorite occurs at Subig, Luzon. It is medium to fine grained, 

 inequigranular, consertal, and slightly intersertal. It consists of zonal labradorite, 

 with a marginal zone of more alkalic plagioclase and some intersertal areas of 

 graphic quartz in alkalic feldspar. The pyroxene is subhedral, and is completely 

 utilized. There is some secondary compact amphibole, and considerable magnetite. 

 The rock is an altered quartz-bearing gabbro. 



Diorites, which are plagioclase rocks characterized by notable amounts 

 of primary hornblende, are related to hornblende-gabbro on the one hand, 

 and to quartz-biotite-diorite, on the other. They may be confused with 

 metadiorite, in which the hornblende is not pyrogenetie. 



Near Atimonan, Tayabas Province, there is a medium-grained, inequigranular, 

 consertal diorite, which may possibly be hornblende-gabbro. The labradorite is 

 like that common in gabbro; without zonal structure, and containing numerous 

 rod-like inclusions. The hornblende is anhedral and green, with numerous rounded 

 inclusions. There is a small amount of mica altered to chlorite. Magnetite is 

 in part intersertal. 



Hornblende-pyroxene-diorites are found in the river gravel at Montalban, Rizal 

 Province. They vary in texture from that of normal diorite to that of holocry- 

 stalline andesite, indicating that these diorites are coarser-grained intrusive 

 andesitic magmas like those erupted as lavas from the volcanoes. 



One variety is medium to fine grained, with inequigranular, consertal, seriate 

 fabric, with intersertal portions. The plagioclase is labradorite considerably 

 altered, somewhat zonally developed, in equant and tabloid anhedrons. The horn- 

 blende is brownish, and anhedral. TJralitized pyroxene is present, and magnetite. 

 There is much chlorite, epidote and some quartz. 



Another specimen, which is altered, contains much labradorite, colorless augite, 

 hornblende and a small amount of brown biotite and magnetite. Still another 

 variety from the same gravel is slightly coarser, with the same type of fabric, 

 but with larger areas that are intersertal between feldspar crystals. These inter- 

 sertal portions are in part poikilitic, or graphic, pyroxene and green hornblende 

 anhedrons. The inclosed mineral is alkalic feldspar without striations, orthoclase 

 or albite. In some instances the pyroxene and hornblende are intergrown with 

 each other. The augite is colorless and abundant, and is not all poikilitic. The 

 hornblende is pale green to colorless. 



A finer-grained variety from Sta. Inez, Rizal Province, is seriate porphyritic, 

 with small amount of groundmass. The phenocrysts of plagioclase (AbjAnj) are 

 rectangular, prismoid or bladed euhedrons and subhedrons, with zonal structure; 

 the outer zone being more alkalic. The hornblende and pyroxene phenocrysts 

 are anhedral. The groundmass consists of rectangular prismoid and equant 

 euhedral plagioclase, with some anhedral quartz, and a small amount of alkalic 

 feldspar, probably orthoclase. There is brownish-green hornblende in the ground- 

 mass which is poikilitic with small chadacrysts of feldspar. There is a small 

 amount of altered mica in the rock. This rock is a fine-grained hprnblende- 

 pyroxene-diorite, or holocrystalline horsiblende-pyroxene-andesite. 



