PETROGRAPHY OF IGNEOUS ROCKS OF PHILIPPINES. 167 



The pyroxene is in subhedral stout prismoids, and is pale green augite with com- 

 pletely altered orthorhombic pyroxene in smaller amount. The augite is also 

 partly uralitized. Magnetite occurs in rather large subhedrons. There is a very 

 small amount of anhedral quartz, intersertal to the other minerals. 



On Grande Island, Subig Bay, there is norite, or gabbro rich in hypersthene. 

 It is fine-grained, inequigranular, consertal, and some varieties are distinctly 

 seriate with a slightly intersertal fabric. The feldspar and ferro-magnesian 

 minerals are in nearly equal proportions. The feldspar in labradorite (Ab.An,). 

 The pyroxene is mostly hypersthene; some crystals exhibiting laminated inter- 

 growth with monoclinic pyroxene. Green hornblende forms borders about some 

 crystals of hypersthene. The magnetite is anhedral and partly surrounds labra- 

 dorite and hypersthene with curved forms, as a synchronous and also a later 

 crystallization. In the variety of the rock with intersertal fabric, the smaller, 

 intersertal crystals are labradorite, pyroxene, hornblende and magnetite. The 

 relative positions and shapes of the minerals indicate that while there was 

 synchronous crystallization, labradorite was the first to begin, then pyroxene, 

 and lastly magnetite. This rock has the same mineral composition as some of the 

 pyroxene-andesites in the neighboring region, and the larger crystals are about 

 the size of the phenocrysts in many of these lavas. 



A very fine-grained norite occurs on Palawan, having the composition approxi- 

 mately of 50 per cent feldspar, 40 per cent pyroxene, 10 per cent magnetite. The 

 fabric is nearly equigranular consertal. The labradorite is anhedral and somewhat 

 larger than the crystals of pyroxene. They contain small inclusions of euhedral 

 pyroxene and magnetite. The pyroxene is mostly hypersthene, in nearly equant 

 subhedrons and rounded anhedrons. 



Gabbros with ophitic fabric which are sometimes called "diabase," 

 dolerite, or phanerocrystalline basalt, occur in numerous localities in the 

 Archipelago, but most of those already collected are more or less decom- 

 posed, or metamorphosed. They are characterized by prismoid, or tabular 

 plagioclase, with diverse, less often subparallel, arrangement; and by 

 poikilitic, or intersertal, pyroxene that acts as a matrix for the feldspar. 

 They grade into varieties in which the intersertal matrix is formed of 

 several crystals of more than one mineral, as in some basalt. 



The ophitic gabbro, or dolerite, from Malirong Falls, Leyte, is ophitic. and 

 seriate, with about equal amounts of feldspar and ferro-magnesian minerals. The 

 plagioclase is altered. The augite is in part poikilitic, and is colorless in thin 

 section, with a purplish outer zone. There is considerable magnetite which is in 

 part intersertal between the crystals of augite and feldspar. There are some 

 chloritized, or serpentinized, crystals which may have been olivine. They are 

 subhedral in form, and quite abundant. 



Other rocks of this kind occur in gravel in the Baliuag River, Bulacan Province; 

 some varieties being coarse-grained, others extremely fine-grained, they also occur 

 in the river gravel at Montalban. A dolerite, from Angono, Rizal Province, has a 

 fabric related to ophitic, and consists of rectangular prismoid plagioclase in 

 diverse arrangement, with much less abundant augite, in euhedral and subhedral 

 prismoids, and also in anhedrons intersertal to the feldspar crystals; the augite 

 is colorless with a brownish outer zone. Magnetite occurs in relatively large 

 skeleton-like anhedrons. There are some serpentine pseudomorphs of olivine, and 

 considerable chlorite. 

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