Goethite
Mineral FeO(OH)
Also called Needle ironstone and Limonite (in part)
About it
Velvety black crusts, radiating needles, and botryoidal masses with a yellow-brown streak, which tells it from hematite. Most 'limonite' is goethite; fine specimens come from Cornwall, Colorado's Pikes Peak, and Germany.
- Type
- Mineral
- Group
- Hydroxide, diaspore group
- Formula
- FeO(OH)
- Hardness (Mohs)
- 5–5.5
- Specific gravity
- 3.3–4.3
- Streak
- yellowish brown to orange-yellow
- Lustre
- adamantine (diamond-like), submetallic, silky, earthy
- Crystal system
- Orthorhombic
- Colours
- black, dark brown, yellow-brown, reddish brown
- Transparency
- opaque, translucent
- Cleavage and fracture
- perfect in one direction; uneven fracture
Typical values: real specimens vary. For more, see mindat.org.