GREENLANDITE
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 (see
fuchsite schist near the bottom of this page).
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:
~Paleoarchean-Eoarchean boundary (depending on which time scale one uses), 3.8
billion years.
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.