Black sand is a heavy, weakly magnetic, glossy, semi-metallic mixture of usually fine sands, found as part of a placer deposit.
Black sands are used by miners and prospectors to indicate the presence of a placer formation. Placer mining activities produce a concentrate that is composed mostly of black sand. Black sand concentrates often contain additional valuables, other than precious metals: rare earth elements, thorium, titanium, tungsten, zirconium and others are often fractionated during igneousmagma processes into a common mineral-suite that later becomes black sands, after weathering and erosion.
Several gemstones, such as garnet, ruby, sapphire, and diamond are found in placers and in the course of placer mining, and sands of these gems are found in black sands and concentrates. Purple or ruby-colored garnet sand often forms a showy surface dressing on ocean beach placers.
Blacksand can be seen as a layer on top of silica sand in regions with high wave energy, on the flanks of volcanoes, and in areas where most of the source rock is mafic, or dark-colored and poor in silica.
The west coast has a great deal of this type of rock, and much of the flsand found on beaches in that region come from rocks like this one.
The dark minerals in beach sand at right, from Fort Funston, (Golden Gate National Recreation Area, California) are primarily magnetite and amphiboles, which are non-magnetic fl minerals.
Blacksand can be seen as a layer on top of silica sand in regions with high wave energy, on the flanks of volcanoes, and in areas where most of the source rock is mafic, or dark-colored and poor in silica.
These are eroded by wave action and are broken into grains and clasts which are included in the flsand.
The dark minerals in beach sand at right, from Fort Funston, (Golden Gate National Recreation Area, California) are primarily magnetite and amphiboles, which are non-magnetic fl minerals.
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