128 B. K. EMERSON — PLUMOSE DIABASE AND PALAGONITE 



Figure 2. — Partially remelted pyroxene crystal (X 40). 



The right central part is the pyroxene remnant (h) with the pris- 

 matic cleavage horizontal. In the transition band the basal part- 

 ing is developed (vertical in the figure) and continues both in the 

 broad, dark-shaded band {g), which is non-polarizing glass, and in 

 the broad, lighter shaded bands on each side, which are devitrified 

 glass {dg), and which ends outwardly in a fringe of glass threads 

 full of magnetite grains — the original resorption rim (rr) around 

 the outside of the crystal. Outside this is the quartz ground full 

 of feldspar microlites. Then comes a broad band of calcite grains 

 (c), containing glass clots {g), which is intercrystallized with the 

 normal pyroxene-plagioclase ground (see page 100). 



Figure 3.— Skeletonized magnetite and poikilitic plagioclase. 



If a diameter be drawn from the lower right to upper left the left 

 half of the figure is a single plagioclase crystal, coarse poikilitic 

 with augite on the upper and fine poikilitic on the lower half. 

 The large black spots are clear yellow glass. The lines of mag- 

 netite run across the slide like the strings of a harp. They seem 

 to blend in broad black patches, because they inclose portions of 

 the same yellow glass, which photographs black (see page 102). 



Plate 28. — Glass Spherulites 



The first four drawings on this plate are of single particles of glass, which were 

 surrounded by the bluish aphanitic holyokeite ground and in- 

 closed in the coarse glass-bearing diabase. 



Figure 1. — Transparent calcite (X 6). 



The crystal is a rhombohedron of colorless transparent calcite, with 

 lustrous faces, inclosed in jet black palagonite, which has pene- 

 trated the crystal along the twinning plane —J R and also irregu- 

 larly. The finer lines are cleavage (see page 118). 



Figure 2. — Calcite spherulite (X 15). 



A central grain of calcite, not seen in the drawing, is surrounded by 

 a sphere of glass, which forms a nucleus around which a layer of 

 calcite rhombs crystallize, followed by a second layer of glass, and 

 so on. The outer layer of calcite is made of large and perfect 

 crystals, always the primary rhombohedron (see page 118). 



Figure 3.— Calcite spherulite (X 4). 



The spherulite is broken across so as to show the drusy surface of a 

 calcite sphserocry stal and the blue radiate quartz. The black glass 

 shows a botryoidal interior from collapse (see pages 102, 119). 



Figure 4.— Collapsed glass cavity (X 2). 



Showing on the black glass wall distinct crystals of calcite and 

 sphserocrystals of calcite-ankerite and deep blue quartz radiate 

 from the edges (see page 119). 



