sedimentary

Hematite Concretion

Iron oxide (Fe2O3) in concretionary form

AI-generated identification · may be incorrect

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

Identified June 30, 2026More sedimentary →

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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).