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Updated: May 25, 2025
If the base be greenstone, basalt, or pitchstone, the rock may be denominated greenstone-porphyry, pitchstone-porphyry, and so forth. The old classical type of this form of rock is the red porphyry of Egypt, or the well-known "Rosso antico." RED QUARTZIFEROUS PORPHYRY is a much more siliceous rock, containing about 70 or 80 per cent of silex, while that of Egypt has only 62 per cent.
The ores were divided into rich and quartziferous; the former not being again melted, but the latter being subjected to a powerful and persistent roasting, during which, after a part of the sulphur, antimony, and arsenic had been exhaled, a kind of distillation of sulphate of copper and sulphate of iron took place, which appeared as "stone," or in balls on the surface of the quartz, and could be easily detached.
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