﻿240 SMITH. 



BENGUET NO. 13. — DIORITE. 



This slide is from a diorite also, but one which is not so fresh. It con- 

 tains triclinic feldspars, most probably labradorite, as the following figures 

 were obtained from Carlsbad twins, 20° to 26° and 11° to 12°. One very 

 noticeable feature of this slide is the great number of small, rounded 

 grains of quartz and feldspar in the interstices of the plagioclases. The 

 slides give the appearance of the rock having suffered a granulation and 

 recrystallization in some portions. This hypothesis is apparently sup- 

 ported by the appearance of some of the feldspars. One in particular 

 is something like Plate I, fig. 2. The characteristic alteration in zones 

 in the plagioclase is shown in Plate I, fig. 2. In one of the Carlsbad 

 twins a structure very similar to what is known as microperthitic is to 

 be seen. 



The amphibole is of the green, pleochoroic variety, actinolite, but 

 much altered. 



The above figures on the Carlsbad twins are supported by investigation 

 of other slides from the same rock where sections normal to the albite 

 twinning gave 31° to 33° maximum extinction, proving pretty conclu- 

 sively that the feldspar is labradorite. The structure of this rock may be 

 termed hypidiomorphic granular to cataclastic. 



BENGUET NO. 16. — DIORITE. 



This slide is largely made up of plagioclase feldspars which show 

 much polysynthetic twinning. No twinning other than the Albite was 

 noted. The other minerals are magnetite, chlorite and calcite, these 

 latter being very intimately associated, as they are all undoubtedly 

 products of the alteration of the feldspars. 



As far as the feldspars are concerned, the structure is described by 

 Eosenbusch's term pan-idiomorphic, and pan-idiomorphic-granular with 

 reference to the whole rock. The feldspars were apparently the first to 

 crystallize from the magma. In some sections the structure is almost 

 that of a porphyry. 



No good sections suitable for measuring extinction angles of the 

 plagioclase were found, although from the presence of the calcite one 

 would infer that they belonged to the lime end of the series. Some of 

 these feldspars show a structure closely resembling what is termed 

 microperthitic, and which is usually produced by an intergrowth of two 

 or more kinds of feldspar. 



The chlorite is the light green mineral with low index of refraction, 

 it is scattered in flakes and stringers all through the slide. However, it 

 has not been seen anywhere in the slide to possess a radial structure, 

 usually so prominent in the case of this mineral. 



In several patches in the slide the three minerals, magnetite, chlorite 

 and calcite are grouped indiscriminately together as if resulting from 

 the alteration of some former ferromagnesian mineral, rich in calcium, 



