Romania 1985 set of 6 stamps

The issue depicts Quartz and Calcite (50B), Native Copper (1L), Gypsum (2L), Quartz (3L), Stibnite (4L) and Tetrahedrite (5L).

Gypsum is a mineral composed of Calcium and Sulphur.
Stibnite is composed mainly by Sulphur.
Tetrahedrite is a mineral with Composition of Iron and Zinc, with some Silver, Copper and Mercury.