Abstract

"Basalt groundmass textural nomenclature is reviewed and revised. The intergranular and ophitic textures are seen as end members of a series with steadily increasing grainsize, the intermediate representative of which is here termed the isogranular' texture. Under intrusive conditions the series may be extended to include the poikilitic texture. Ophitic texture is regarded as an intergrowth; the term 'sub-ophitic' is not suitable for basalts but may be retained for texturally isotropic rocks. When basalts cool hurriedly they will tend to develop an intergranular texture whereas extension of the crystallization period permits the formation of an aphitic texture. Cooling conditions will be determined by a combination of the effects of the volatile concentration and the flow characteristics, the latter partly depending on topography."

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