sedimentary
Hematite Concretion
Iron oxide (Fe2O3) in concretionary form
Hardness: 5.5-6.5; Color: Dark brown to metallic gray, often with reddish oxidation; Luster: Dull to sub-metallic; Crystal structure: Trigonal; Cleavage: None; Specific gravity: ~5.3.
- Hardness
- 5
- Color
- Dark brown to metallic gray, often with reddish oxidation
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5.5-6.5; Color: Dark brown to metallic gray, often with reddish oxidation; Luster: Dull to sub-metallic; Crystal structure: Trigonal; Cleavage: None; Specific gravity: ~5.3.
Formation & geological history
Formed by the precipitation of iron oxide minerals from groundwater within the pore spaces of sedimentary rock (typically sandstone or shale). These often form around a nucleus such as a fossil or grain of sand.
Uses & applications
Used as an ore of iron, in jewelry as semi-precious beads, and as decorative curiosities (e.g., 'Moqui Marbles' or 'Blueberries').
Geological facts
A famous occurrence of these concretions was discovered on Mars by the Opportunity rover, often referred to as 'Martian Blueberries,' indicating the past presence of water.
Field identification & locations
Identify by its heavy weight (high density) for its size and its reddish-brown streak when rubbed on unglazed porcelain. Commonly found in desert regions of Utah (Navajo Sandstone).
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