Porphyry (Gr. Porphyry 1300657 , purple), a rock so named from the prevalent color of the varieties used by the ancients, as the rosso antico or red porphyry of Egypt. This variety consists of a ground or paste of reddish feldspar in which are disseminated rose-colored crystals of the feldspar called oligoclase, with some plates of blackish hornblende and grains of peroxide of iron. This in general is the character of porphyry; but the paste may be green, red, purple, or black, and the interspersed crystals may present various shades, usually lighter than the ground. They may be also of hornblende, quartz, augite, olivine, and other minerals. The rock is very hard. On the smooth surface the crystals appear as blotches. Various rocks of an earthy or compact base with distinct interspersed crystals are termed por-phyritic. Granite is so called when it presents distinct feldspar crystals, and so are greenstone, trachyte, etc. The principal uses of porphyry are in architecture and ornamental articles, and in slabs and mullers for grinding hard powdered substances to extreme fineness. No material is more durable, and none retains better the sharp lines and high polish which it receives.

In modern times it is most successfully worked by the Swedes and Russians. In the Swedish royal porphyry works of Dalecar-lia vases, tazze, etc, of immense size are made, one of the latter exceeding 11 ft. in diameter. A vase of pink granitoid porphyry 6 ft. high and 4 ft. 4 in. in diameter was sent to the great exhibition in London in 1851. In the United States porphyry is met with in granitic regions.

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Porphyry (Gr. Porphyry 1300658 , i. e., a wearer of purple), a philosopher of the Neo-Platonic school, born in Batanea or in Tyre about A. D. 233, died in Rome about 305. He was of distinguished family, and was originally named Malchus, the Greek form of the Syro-Phoe-nician Melech, signifying king; but he received from his preceptor Longinus, in allusion to the meaning of that word, the name by which he has ever since been known. He studied under Origen at Caesarea, under Apollonius and Longinus at Athens, and at Rome under Ploti-nus, with whom he remained six years, at the end of which period he went to Sicily, where he wrote his treatise against the Christian religion. He subsequently returned to Rome, and taught there for many years. The philosophical doctrines of Porphyry were essentially those of Plotinus, which he regards as identical with those of Plato, and substantially also with those of Aristotle. His doctrine is distinguished from that of Plotinus by its more practical and religious character.

The worship of the national gods of a people seems to have been upheld by him, on the ground that respect should be shown to the ancient religious usages of a nation; but he acknowledged one absolute supreme Deity. He wrote expositions of Plato's "Timseus" and "Sophistes" and of Aristotle's Categories and Be Interpretations, and a still extant isagogical work on Aristotle, which is usually printed at the beginning of the Orga-non. Of his 56 different works mentioned, only 19 are extant. The most celebrated of his lost works is that "Against the Christians," which was publicly destroyed in 435 by order of the emperor Theodosius II. It was in 15 books, and treated both the Jewish and Christian Scriptures very minutely. In it he denied the doctrine of the divinity of Christ, and maintained that the prophecies of Daniel were written after the events. His Vita Plo-tini, composed shortly before his death, appeared first in the Basel edition of the En-neads (1580). The most recent commentators on Porphyry's life and works are Brandis, Wolff, Bernays, Schafer, and Baltzer.