Goethite
| Colour | Brown, Yellow, Black |
|---|---|
| Mohs hardness | 5.0–5.5 |
| Lustre | Adamantine to dull |
| Streak | Brown, brownish yellow to orange yellow |
| Crystal system | Orthorhombic |
| Cleavage | Perfect {010} |
| Fracture | Uneven to splintery |
| Chemical formula | α-FeO(OH) |
| Specific gravity | 3.3–4.3 |
What is Goethite?
Goethite is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the α-polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient times for its use as a pigment. Evidence has been found of its use in paint pigment samples taken from the caves of Lascaux in France. It was first described in 1806 based on samples found in the Hollertszug Mine in Herdorf, Germany. The mineral was named after the German polymath and poet Johann Wolfgang von Goethe (1749–1832).
How to identify Goethite
- Lustre: Adamantine to dull.
- Hardness: Mohs 5.0–5.5 — soft; a knife will scratch it.
- Streak: Brown, brownish yellow to orange yellow.
- Habit: Orthorhombic crystal system.
Goethite in different forms
Stones often confused with Goethite
Frequently asked questions
How hard is Goethite?
Goethite is Mohs 5.0–5.5 on the hardness scale.
What colour is Goethite?
Goethite is typically brown, yellow, black (Yellowish to reddish to dark brown or black).