Proustite
Proustite was named after the French chemist J.L.Proust (1754-1826). It consists of columnar polar terminations, also rhombohedral or granular and lump aggregates, coatings or grains. Fresh is vermilion red, unfortunately it quickly darkens in the light, turns gray to black. Occurs on polymetallic hydrothermal veins.
More info
Proustite was named after the French chemist J.L.Proust (1754-1826). It consists of columnar polar terminations, also rhombohedral or granular and lump aggregates, coatings or grains. Fresh is vermilion red, unfortunately it quickly darkens in the light, turns gray to black. Occurs on polymetallic hydrothermal veins.