GOETHITE
Goethite is an iron hydroxy-oxide mineral,
FeO(OH). It has a nonmetallic luster, is usually brown to dark brown in
color, has a brownish streak, no cleavage, and is moderately hard (H=5 to
5.5). It typically forms by the oxidation of iron-rich minerals.
Goethite forms crystals or fibrous masses of varying morphology, but many
samples are massive.
Goethite
(3.3 cm across)
Goethite
from a bog iron mine in Lancaster County, Pennsylvania, USA (public display, Carnegie
Museum of Natural History, Pittsburgh, Pennsylvania, USA.
Goethite
that has replaced a mass of gypsum crystals (hydrous calcium sulfate) from the
Cave of Swords, Naica Mine, eastern Chihuahua State, northern Mexico.
Goethite
from the White Desert of Egypt.
Left:
goethite replacing marcasite crystals.
Right:
goethite replacing pyrite crystals.