Greenlandite (fuchsite-quartz gneiss) (2.7 cm across at its widest) from the Precambrian of southwestern Greenland. Green = fuchsite; gray = quartz; a few small, scattered pyrite crystals (brassy gold-colored) are also visible. Attractive greenish-colored gneisses in southwestern Greenland that contain the minerals fuchsite (green) and quartz (gray) have been informally called greenlandite. Fuchsite is a chromian muscovite mica (K(Al,Cr)2AlSi3O10(OH,F)2 - potassium chromium hydroxy-fluoro-aluminosilicate); it is typically encountered in schistose rocks. Greenland greenlandite is part of a 3.8 billion year old, highly metamorphosed succession of rocks. These represent the oldest known supracrustal rocks on Earth (the oldest crustal Earth rocks include 4.03 billion year old Acasta Gneiss, 4.28 b.y. rocks from the eastern Hudson Bay area, and 4.45-4.55 b.y. rocks in the subsurface of Baffin Island, Canada). Locality: undisclosed locality in the Godthåbsfjord area or Nuuk area, southwestern Greenland. Age: Eoarchean boundary, 3.8 billion years.