Of the numerous islands that dot the Gulf many are partly at least of volcanic origin, notably Qishm and Ormuz.
Experimental boring on Qishm I.
Inland from Sur, and some seams of good coal in newer strata; sulphur occurs in a fairly pure state at Khamir and Bustaneh near Lingeh, and on Qishm I.; copper, as copper glance and malachite, occurs in the interior of Oman; copper-mines are said to have been worked in the neighbourhood of the coast near Lingeh by the Portuguese, but all trace of them has been lost.
Red ochre, for which there is only a limited market, is mined on Ormuz, Abu Musa and other islands in the Gulf; salt, as deposits, on Ormuz and Qishm I., and by evaporation, near Mohammerah, Fao and elsewhere on both sides of the Gulf; gypsum is widely distributed throughout the Gulf; iron, as haematite and pyrites, widely found through the Ormuz series.
Earthquakes are frequent and sometimes severe in the Persian Gulf proper, especially on Qishm I.