Heavy mineral sand contains lots of heavy minerals, hence the name. The density of these minerals is generally above 2.9 grams/cm³. Important heavy minerals are magnetite, garnet, ilmenite, zircon, spinel, augite, staurolite, hornblende, rutile, kyanite, tourmaline, biotite, titanite, apatite, etc.
These minerals often occur in sand, but usually in low quantities (less than 1 percent). Sometimes they get concentrated in beaches or river bottoms to form beautiful and unusual-looking sand samples. The composition of these sand samples is highly variable. The most common constituents of heavy mineral sands are garnet, magnetite, ilmenite, and epidote. Most heavy mineral sand samples contain quartz as well, but it is not as important as usual.
The source materials of heavy mineral sand are metamorphic and igneous rocks. Metamorphic rocks give rise to sand containing kyanite and garnet, for example, although the latter may crystallise from magma as well. Magnetite is mostly of igneous origin.
Heavy mineral sand is a natural mineral concentrate which is often mined commercially. Zircon, gold, ilmenite, rutile, monazite, and cassiterite are some noteworthy heavy minerals that are often extracted from sand. Heavy mineral sand is not rare, but its area of occurrence is usually limited.
Magnetite grains from a heavy mineral sand from Guam (Talofofo Beach). These magnetite grains are aligned in the presence of a strong external magnetic field. Width of view 10 mm.
