I have been looking for spherulite feature in felsic volcanics, and I am unable to confirm it. Peculiar spherulites in felsic rocks show dark extinction in cross polar. Are such features essential to present in all spherulites in rhyolite?
Dear Mr. Singh,
spherulitic textures in rhyolites need not be perfectly circular and may have different radii. They consist of alkali feldspar which due to its twins provokes the black and white shades, and glass fully or partially converted into quartz. This is only in parts realized in the radiating textures (upper left) under consideration. What renders me skeptical to speak of a true spherulitic texture is the orientation. Using the clock´s dial you see a texture showing some kind of septaria from 8 to 12 (upper left) and from 9 to 12 (center right) this would be contradictive to their denomination as spherulitic in an otherwise randomly textured groundmass of a felsic magma on consolidation . I do not know anything about the orientation of the thin section. It might also be the case that a vug was filled by the above minerals leading to a radiating texture (?)
With kind regards H.G.Dill
Thank you Prof. Harald G. Dill for your elucidate answer. I am not very convinced to the idea of vug filled by secondary minerals leading to radiating crystals shape because there are more features like this (in picture attached) at various size in this thin section. I am more inclined to spherulite in my case, but still need concepts from others like Prof. Harald.
You have to show us how the thin section is oriented relative to the surface or other planar elements relevant for the evolution of your rhyolite. True radiating aggregates found in these rocks which I examined under the petrographic microscope look very much different from yours and were found in the same random texture as the groundmass. Here you have an orientation which you have to deal with (?)
H.G.Dill
Thank you prof. Harald G. Dill, I will further examine the thin section under petrographic microscope.
Regards,
N. Lakhan
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