Pyrrhotite is an iron sulfide with a non-stochiometric composition and a formula Fe(1-x)S (x = 0 to 0.2). It has a number of polytypes: 5C,6C,7C,11C. Each one can either posses monoclinic or hexagonal symmetry. Hexagonal forms are stable at higher temperatures. Their stability increases with an increasing iron content in the structure. The photo of the sample I depicts hexagonal symmetry.
Bournonite is a sulfosalt mineral with a formula PbCuSbS3. It crystallizes in orthorombic system typically creating tabular crystals with metallic luster. It usually occurs with galena, tetrahedrite, sphalerite – brownish grains in the picture of the sample II.
Orpiment is an arsenic sulfide with a formula As2S3. It can be formed either by sublimation as a hot-springs deposits or in hydrothermal veins. In ancient times it was used as a yellow pigment. It crystallizes in a monoclinic system. It is a soft mineral (Mohs hardness 1,5 to 2,0) with low melting point about 320 °C.
Realgar is as well an arsenic sulfide with a formula AsS. It crystallizes in monoclinic system and it often occurs in association with orpiment. When exposed to the light it decays into mineral so-called pararealgar with the same composition but different structure. It has red colour.