PETROGRAPHY OF IGNEOUS ROCKS OF PHILIPPINES. 157 



abundant than the enhedral, rather large microlites of rectangular, equant 

 and prismoid plagioelase, prismoid pyroxene, and equant magnetite. 



Pyroxene-andesites with holocrystalline groundmass have been found 

 in various localities: Benguet, Ilocos Norte, Masbate, Cebu, and else- 

 where. In some the microlites are crowded together, without matrix of 

 glass, and without any characters that distinguish the groundmass texture 

 notably from many in which there is a slight amount of glass base, except 

 that the form of the microlites is less distinct. In those with slightly 

 coarser crystallization the fabric is characterized by anhedral, equant, 

 micropoikilitic quartz, in indistinctly outlined anhedrons, crowded with 

 minute prismoids of plagioelase and pyroxene, and anhedrons of mag- 

 netite. 



A still coarser variety occurs at Mount Batalao, in southwestern Luzon. 



It is dosemic. that is. the phenocrysts are more abundant than the groundmass; 

 it is mediophyric, with phenocrysts between 1 and 5 millimeters in diameter. 

 There is much labradorite in euhedral crystals, rectangular and tabular, with 

 pronounced zonal structure, in recurrent zones of more or less alkalic com- 

 position; well twinned, and containing many inclusions. There are fewer and 

 smaller phenocrysts of pyroxene, both hypersthene and augite; and still less 

 magnetite. The groundmass is holocrystalline, and consists of small euhedral 

 plagioelase, less pyroxene and magnetite, with intersertal anhedrons of poikilitic 

 quartz, crowded with minute inclusions, (chadacrysts) of plagioelase and alkali- 

 feldspar, probably orthoclase. The intersertal quartzes are chadoikic, that is, 

 there is about as much matrix quartz (oikocryst) as inclusions (chadacrysts). 

 In a somewhat similar, dosemic, mediophyric, pyroxene-andesite from 1 kilometer 

 southeast of Aroroy, ^lasbate, the phenocrysts of pyroxene are larger than those 

 of feldspar, and the larger augites inclose some plagioelase (labradorite), some 

 hypersthene, and magnetite. The hypersthene is altered. The groundmass is 

 itself porphyritic with small euhedral plagioclases in a matrix of consertal, 

 anhedral crystals of more alkalic plagioelase, pyroxene, magnetite, and some 

 quartz. This matrix is intersertal between the euhedral crystals. A similar 

 fabric characterized a slightly altered pyroxene-andesite from Benguet, which is 

 persemic ; that is, has more phenocrysts than groundmass. 



An oliv'ine-bearing pyroxene-andesite occurs at Antipolo, Rizal 

 Province. 



It is dopatic, with preponderance of groundmass; is mediophyric, and has a 

 hyatal to seriate, porphyritic fabric. There are many phenocrysts of labradorite, 

 with abundant inclusions; few of pyroxene and some olivine. The groundmass 

 consists of colorless glass crowded with brown globulites, and many microlites of 

 prismoid plagioelase, equant to prismoid pyroxene, equant magnetite, and many 

 minute, long, needle-like crystals of pyroxene, and lines of globulites, which are 

 undoubtedly pyroxene also. Some are in attached strings, some are disconnected. 

 All the prismoid crystals are diverse in arrangement. This variety of rock is 

 intermediate between andesite and basalt. 



Quite different types of texture from those just described occur in other 

 varieties of pyroxene-andesite. 



One from Union Province is perpatic. with almost no phenocrysts, and these are 

 of plagioelase. The groundmass consists of tabloid plagioelase, sections being 



