What Is Magnetite?
Quick answer
Magnetite is a black iron oxide mineral, and it is usually the most common mineral in a gold panner's black sand. It is strongly magnetic, so a magnet lifts it right out of your pan.
If you pan for gold, you have already met magnetite. It is the black, heavy grit that collects in the bottom of your pan, and it is the part of black sand a magnet grabs. This guide covers what it is, how to tell it from hematite, and what it is used for.
What is magnetite made of?
Magnetite is an iron oxide, written Fe3O4. Together with hematite, Fe2O3, it is one of the two main kinds of iron ore, according to the U.S. Geological Survey's iron ore pages.
Is magnetite magnetic?
Yes, very. Magnetite is the most strongly magnetic mineral found in nature, and it is one of only a few minerals a common magnet will pick up. Some magnetite is a natural magnet all by itself. That kind is called lodestone, and it is usually coated in tiny bits of other magnetic grains it has collected.
What does magnetite look like?
Magnetite is gray black to iron black with a metallic shine. Rubbed on a streak plate it leaves a black streak. It is hard, about as hard as a steel knife blade, and heavy for its size: about 5.1 to 5.2 times as heavy as water, compared with about 2.6 for ordinary quartz sand. In a pan you will mostly see it as small black grains.
Why is magnetite in your gold pan?
Because it is heavy, and heavy things settle together. Moving water drops magnetite in the same slow spots where it drops gold. The USGS names magnetite as the most common mineral in black sand. That is not true of every creek, though. In one area of Idaho, USGS geologists found more ilmenite than magnetite, because groundwater had dissolved much of the magnetite. Our page What Is Black Sand? covers the rest of the mix.
How do you tell magnetite from hematite?
Use two quick tests: a magnet test and a streak test. You need both, because the two minerals weigh almost the same, magnetite about 5.15 and hematite about 5.3. Panning cannot sort them apart. A magnet can.
The magnet test
- Spread a few dry grains on a sheet of paper.
- Bring a magnet close to them.
- Grains that jump to the magnet are magnetite.
- Grains that do not move are probably hematite or another mineral that is not magnetic, like garnet.
- Grains that move only a little may be a weakly magnetic mineral such as ilmenite, or hematite with some magnetite inside it.
Our magnets use a strong neodymium magnet, so keep it away from phones, cards and steel tools while you test. Our safety warnings cover the rest.
The streak test
- Find an unglazed piece of white porcelain. Geologists call it a streak plate.
- Rub a grain or a small pebble firmly across it.
- A black or gray black streak points to magnetite.
- A red brown streak points to hematite, even when the piece itself looks black.
The Utah Geological Survey uses this same test to identify minerals, and it notes that hematite leaves a red streak whatever color the rock is. The streak test works best on a grain big enough to hold.
What if a grain passes both tests?
If a grain jumps to the magnet but leaves a reddish streak, it is most likely a mix of the two. Plenty of hematite carries enough magnetite to be pulled by a magnet.
Why does some of your black sand not lift?
Because it is not magnetite. In a normal pan, our magnet pulls up all the black sand we see. Garnet, zircon and most hematite stay behind, and ilmenite answers only weakly. That is why the last step is always a little more panning. Our guide on how to separate gold from black sand takes you through it, and our black sand magnets are built for the magnet step.
What is magnetite used for?
Mostly making steel. Magnetite is the most commonly mined iron ore, and the USGS reports that 98% of iron ore goes into steelmaking.
The biggest version of the trick a panner does with a magnet happens in Minnesota. There, a hard rock called taconite holds magnetite and only about 25 to 30% iron. Mills grind it to powder, pull out the magnetite with magnets, and roll it into marble sized pellets with over 65% iron, as the USGS describes in its look at the taconite mines.
Magnetite has smaller jobs too. Ground fine and mixed with liquid, it makes a heavy slurry for cleaning coal. It is part of emery, a natural abrasive, and it also goes into paint pigment, printer toner, fertilizer and heavy concrete.
Where is magnetite found?
In many kinds of rock. It shows up in igneous, metamorphic and sedimentary rocks, and some river and beach sands carry a lot of it. For a gold panner, the most common place to meet it is in the black sand at the bottom of the pan.
