Small opal occurence is located in the serpentinite rocks near the Rožná village, Czech Republic. It yields uncommon opal material with reticulated structures, some of these opals also contain chromite.
Melanterite is a perishable product of iron ore weathering, forming awesome green stalactites and crusts in the abandoned mines. Its shaky existence is a nice example of natural processes, but admiring melanterite beauty often includes trips to hardly accessible underground places.
Cinnabar is bright red mercury sulfide, which is a main ore of mercury and used to be a source of red pigments for milleniums. Cinnabar (and mercury) had been a key to mining precious metals until beginning of the 20th century and also saved a millions of teeth.
Magnesite is not the most popular mineral for collectors but it can form outstanding specimens and crystals. However, its principal use is as a magnesium ore and a special refractory - a material where resistance to extreme temperatures is fundamental to an industrial process.