1894. 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



667 



Fiji. 8. 



POI.VSOMATIC OLIVINES. 



Miitfi, i; S. N, M. 



glass cavities. A cliloritic or serpentiuous alteration has set in and 



tlie crystals are traversed by the characteristic irregular canals of 



brightgreenish blue secondary 



matter and scattering grains 



of iron ore. The angites occur 



in sizes fully equal to those of 



the olivines, and are of a clear 



light green or faint yellow 



color in section. They con- 

 tain very numerous inch)sures 



of the groundmass, a brown 



dichroic minernl, evidently 



mica, grains of iron ore, and 



glass. As a rule, the crystal 



outlines are far from perfect, 



the )nineral having suffered 



from the corrosive action of 



the magma even nun-e than tlie 



olivine. The mineral is i)er- 



fectly fresh and clear, shows 



sharply developed prisniati*- 



cleavages a^id gives maximnm extinctions on clinopinacoidal sections 



of 4.3°. Like the olivine, it occurs both in scattered and isolated single 



crystals and in groups. Twin 

 forms are common after the 

 ordinary- tyjx'. Augite and 

 olivines often occur in such 

 close Juxtaposition as to 

 have nnituallj^ interfered in 

 j)rocess of growth (see fig- 

 ure U). So marked an inter- 

 fcience between minerals 

 belonging to the earliest 

 stages of consolidation and 

 occurring in widely scat- 

 tered groui)S in an unindivid- 

 ualized groundmass can be 

 accounted for only on the 

 supposition that neither min- 

 eral is a direct secretion from 

 the magma, but that they 

 are residuals of an earlier 

 crystallization in which con- 

 solidation had proceeded so 

 far that free growth was no 

 longer possible. The pres- 

 ent rounded, scattered, clustered, or isolated conditions being due to 



INTERGROWN OLIVINES AM) AUC.ITE. 

 a.— Olivines. /<.— Augite. 



From specimen No. 3aW6, I'. S. N. M. 



