Porphyritic adj. (Min.) Relating to, or resembling, porphyry, that is, characterized by the presence of distinct crystals, as of feldspar, quartz, or augite, in a relatively fine-grained base, often aphanitic or cryptocrystalline.
... close up to it stand the famous blue-stones, now twelve in number, but originally perhaps more. These stones are not so high as the trilithons, the tallest reaching only 7-1/2 feet. They are nearly all of porphyritic diabase. It has often been asserted that these blue-stones must have been brought to Stonehenge from a distance, as they do not occur anywhere in the district. Some have suggested that they came from Wales or Cornwall, or even by sea from Ireland. Now, the ... — Rough Stone Monuments and Their Builders • T. Eric Peet Read full book for free!
... geological structure of the lands through which we had passed as follows: The pantanals were of Pleistocene age. Along the upper Sepotuba, in the region of the rapids, there were sandstones, shales, and clays of Permian age. The rolling country east of this contained eruptive rocks—a porphyritic disbase, with zeolite, quartz, and agate of Triassic age. With the chapadao of the Parecis plateau we came to a land of sand and clay, dotted with lumps of sandstone and pieces of petrified wood; this, according to Oliveira, is of Mesozoic ... — Through the Brazilian Wilderness • Theodore Roosevelt Read full book for free!
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