porphyrite, porphyryte

[English por phyr(y), and suff. -ite ( Petrol. ).] Petrol .: A name used by some petrologists for the porphyritic orthoclase rocks which are free from quartz. Some, however, include varieties in which the orthoclase constituent is more or le replaced by oligoclase. Many porphyritic dolerites have been also included under this name. By the presence of hornblende it often approaches the composition of a syenite (q. v.), with which it is frequently IMG:content-1347.png:[blocks in formation] IMG:content-1348.png:[blocks in formation] Tus.) The principle of succe ion in royal families, and especially among the Eastern Roman emperors, by virtue of which a younger son, if born in the purple," that is, after the succe ion of his parents to the throne, was preferred to an older son born previous to such succe ion.