Goethite
FeO(OH)IMA symbol: Gthapproved
Goethite is an oxide or hydroxide mineral with the formula FeO(OH), crystallizing in the orthorhombic system. It has a Mohs hardness of 5-5.5, typically black, brown, red or yellow in color, with an adamantine luster, a specific gravity of 4-4.4. Its streak is brown or yellow.
Photos
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Crystallography
| Crystal system | orthorhombic crystal systemWikidata (CC0) |
|---|---|
| Space group | P b n m |
| Cell (Å, °) | a = 4.6048, b = 9.9595, c = 3.023; α = 90, β = 90, γ = 90 |
| Cell volume | 138.6 ų, Z = 4 |
| Axial ratios | 0.4624:1:0.3035calculated from COD 1008768 |
| Source structure | COD 1008768 (Materials Science Forum, 1991) — 1 of 21 structures |
Powder X-ray diffraction (calculated)
| d (Å) | 4.18 | 2.449 | 2.693 | 1.719 | 1.564 | 2.584 |
|---|---|---|---|---|---|---|
| I/I₀ | 100 | 70.9 | 42.9 | 38.4 | 25.5 | 25.1 |
xrd-v1: CuKa1 1.5406A, 2theta 5-90, top10, Imax=100, no DW/PO. Computed from COD 1008768; idealized occupancies, no preferred orientation.
Physical properties
| Density (calculated) | 4.233 g/cm³calculated from COD 1008768 |
|---|---|
| Hardness (Mohs) | 5-5.5single sourceDana, System of Mineralogy, 6th ed. (1892) |
| Specific gravity | 4-4.4 g/cm3corroboratedDana, System of Mineralogy, 6th ed. (1892) |
| Color | black, brown, red, yellowsingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Streak | brown, yellowsingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Luster | adamantinesingle sourceDana, System of Mineralogy, 6th ed. (1892) |
Chemistry (calculated)
| Molecular weight | 88.85 g/molcalculated from the IMA formula |
|---|---|
| Composition (wt%) | Fe 62.85%, O 36.01%, H 1.13% |
Classification
| Nickel-Strunz (10th) | 4.FD.10Wikidata (CC0) |
|---|---|
| Nickel-Strunz (9th) | 4.FD.10Wikidata (CC0) |
| Dana (8th) | 6.1.1.2Wikidata (CC0) |