sedimentary
Black Sand (Magnetite/Heavy Mineral Concentrate)
Magnetite-rich Placers (Fe3O4)
Hardness: 5.5-6.5 (for magnetite grains); Color: Black, charcoal grey, or dark silver; Luster: Metallic to sub-metallic; Crystal Structure: Isometric (often rounded grains); Specific Gravity: 5.17-5.18. Often magnetic.
- Hardness
- 5
- Color
- Black, charcoal grey, or dark silver
- Luster
- Metallic to sub-metallic
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Physical properties
Hardness: 5.5-6.5 (for magnetite grains); Color: Black, charcoal grey, or dark silver; Luster: Metallic to sub-metallic; Crystal Structure: Isometric (often rounded grains); Specific Gravity: 5.17-5.18. Often magnetic.
Formation & geological history
Formed through the mechanical concentration of high-density mineral grains by water or wave action. These minerals usually derive from the weathering of igneous rocks (like basalt or andesite) and are concentrated in riverbeds or coastal beaches as 'placer deposits'.
Uses & applications
Used as an ore of iron, in industrial abrasive manufacturing, and as a common indicator for gold prospecting (as gold often settles in the same heavy-mineral layers).
Geological facts
The regional coordinates (Papua New Guinea area) are geologically active with volcanic arcs, making magnetite-rich sands very common. Many black sands in this region are associated with porphyry copper-gold systems.
Field identification & locations
Identified by its dark color, high weight compared to common sand, and strong attraction to a magnet. Commonly found in the bends of rivers or along volcanic coastlines.
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