Hematite (Kidney Ore variety)
Hematite (Iron Oxide) · Mineral Specimen / Industrial Mineral
Crystal System
Trigonal; this specimen shows a massive to botryoidal habit with a thick, iron-rich oxidation crust.
Mineral Group
Oxides (Hematite group)
Chemical Formula
Fe2O3
Formation Process
Primarily formed through the oxidation of iron-rich minerals in sedimentary iron formations or via hydrothermal precipitation in veins and cavities.
About This Crystal
An opaque, heavy mineral specimen with a dull to sub-metallic dark grey surface. It features a prominent brownish-red oxidation rim (limonite/rust) and a slightly granular, weathered texture on the flat face.
Physical Characteristics
Color: Gunmetal grey to black; Streak: Distinctive rust-red to cherry-red; Cleavage: None; Fracture: Uneven to sub-conchoidal; Specific Gravity: 5.26; Magnetism: Weakly magnetic after heating; Fluorescence: None.
Optical Properties
Opaque; Refractive Index: 2.94-3.22 (high but not measurable by standard refractometers); Birefringence: Very high (but masked by opacity); Luster: Sub-metallic to earthy.
Hardness & Durability
Origin Region
Commonly found in Cumbria (UK), Morocco, and the Great Lakes region (USA). This specimen likely originates from a sedimentary or hydrothermal iron deposit.
Hardness & Durability
Mohs Hardness: 5.5 - 6.5. Brittle tenacity; high density makes it feel heavier than it looks. Relatively stable but prone to further oxidation if kept in damp conditions.
Care & Maintenance
Keep dry to prevent further rusting of the outer layers. Clean with a soft, dry brush. Avoid acids which can etch the surface. Store separately to prevent scratching softer minerals.
Rarity & Value
Very common; value is primarily as a geological specimen or iron ore. Decorative pieces are affordable, typically ranging from $5 to $30 depending on size and luster.
Special Characteristics
Displays a characteristic red streak even when the surface appears black. This specimen shows a 'crust' or 'rind' of secondary iron oxides (limonite/goethite) known as 'gossan' in mining terms.
Lore & History
Used since the Paleolithic as red ochre pigment for cave paintings. Romans associated it with Mars (God of War) due to its blood-red streak. In modern lore, it is believed to be a 'grounding' stone and an aid for blood-related disorders.