porphyroidal

Updated: May 21, 2026

When they are very small, they give the clay a porphyroidal appearance. We find disseminated in it, as we have already observed, either in nests or in small veins, selenite, and sometimes, though seldom, fibrous gypsum.

Alexander von Humboldt - Personal Narrative of Travels to the Equinoctial Regions of America, During the Year 1799-1804 — Volume 1