118 B. K. EMERSON — PLUMOSE DIABASE AND PALAGONITE 



and magnetites had been pushed to an extreme the residual and still 

 liquid magma having about the composition of the holyokeite seems to 

 have been sometimes squeezed out into minute fissures formed by shrink- 

 age or explosions in the newly consolidated schlieren — fissures so small 

 that the large crystals could not enter there. Thus were formed the nar- 

 row dikes of almost normal holyokeite, and within them was completed 

 a differentiation into palagonite and holyokeite like that in the coarse 

 diabase ground, and the last of the long albite microlites thrust them- 

 selves clear across the palagonite clots from all sides, and in their rapid 

 formation included a core of glass. 



FORMATION OF THE GLASS WITH CALCITE SPHERULITES 



In the supersaturated, unstable, and imperfectly blended magma the 

 consolidation was extremely rapid, and antagonistic processes went on 

 almost at the same time and place. The earlier formation of the holy- 

 okeite base described above and its growth into the residual glass is only 

 a part of the process. The abstraction of the albite molecule made the 

 glass supersaturated for the Ca and Mg carbonates, while the presence 

 of the mineralizers abnormally prevented it from being supersaturated 

 for iron. 



Another form of solidification in this glass (see plate 28, figure 1) then 

 commenced with a minute crystal of calcite, always in the primary 

 form, which sometimes grew in the magma to be 2 to 3 millimeters 

 across, including threads of glass, or a small aggregate of such crystals 

 formed and was surrounded by glass. By the absorption of heat in crys- 

 tallizing or the abstraction of CaC0 3 from the adjacent magma, or both, 

 the crystal becomes the cause of solidification for the latter, and a broad 

 zone of glass uniformly surrounds the calcite. 



Again (see plate 28, figure 2), the first grain of calcite causes, as above, 

 the solidification of a thin, spherical layer of glass around itself — just 

 the layer that has been changed and made less fusible by its own crys- 

 tallization. Outside this layer the magma is in its original condition, 

 and quickly a spherical shell of delicate calcite crystals surrounds the 

 nucleus, and this is in turn the cause of the solidification of a second 

 layer of glass, and this operation is repeated five or six times, forming 

 beautiful spherulites as large as a small shot (3 to 5 millimeters). Some- 

 times at the end a single crystal grows large and destroys the symmetry. 

 In every case the calcites have sharp angles and lustrous faces, and the 

 delicate feathery groups are so exactly enveloped in the fresh shining 

 glass that even when they are not in spherulites the idea that the calcite 

 has been swept in from some foreign source as solid crystal fragments 

 can not be entertained. Both are ideally fresh and rest in ideally 



