Oxide of Chromium or Chromium Green was discovered in the mid-19th Century and made from a metallic oxide.
A good solid mid-value green, really useful as base green for landscape painting, neither really too warm nor cool. Good tinting power and definitely opaque.
If you aren't mixing your greens from primaries then this would be an excellent choice on the palette as it can be taken in so many directions. Pigment rich.
Technical Overview
Pigment - PG17
Vehicle - Linseed Oil
Opacity - Opaque
Drying Time - Average