Sandstone with Magnetite and Iron Staining

Physical Properties

Hardness: 6-7 (if quartz-based). Color: Buff to tan with reddish iron-oxide staining and black cubic/octahedral crystals. Luster: Dull (matrix) to metallic (crystals). Crystal structure: Granular matrix with isometric crystals. Specific gravity: Approx 2.3-2.7.

Formation & Geological History

Formed through the accumulation and cementation of sand-sized mineral grains or rock fragments. The black grains are likely detrital magnetite or ilmenite deposited in an ancient beach or river environment, then lithified over millions of years.

Uses & Applications

Primarily used in construction (aggregate, dimension stone) and as a subject for geological study and mineral collecting.

Geological Facts

Magnetite is the most magnetic naturally occurring mineral on Earth. In sandstone, these 'heavy mineral' grains can often map out ancient current patterns within the cross-bedding of the rock.

Field Identification & Locations

Identify in the field by the visible sand grains (feels like sandpaper) and the presence of small, dark, potentially magnetic inclusions. Use a hand lens to see if the black squares exhibit crystal faces. Found worldwide in sedimentary basins.

Identified on: 4/14/2026

Mode: Standard