Magnetite: Ultimate Guide to Magnetite (What It Is and Where to Find It)

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Magnetite is one of the more commonly collected crystals, perhaps being just a bit less common than iron pyrite in collections. Its unique crystalline shape and deep coloration have made it a favorite for many and it’s served an important role in much of human history, for more reasons than one.

So, let’s take a look at magnetite, in our ultimate guide to the mineral.

What is Magnetite?

Magnetite is an iron mineral, specifically, it’s an oxidized form of a balanced blend of iron ions. It contains both divalent (Fe²+) ions and trivalent (Fe³+) ions. It’s most commonly seen as octahedral crystals with a black color, although some may take on a brownish tinge.

labeled magnetite specimen

Being a relatively simple mineral, simply an oxidized form of the two iron ions listed above, it’s very common in the natural world. This commonality led to it being one of the primary ores of iron for much of human history.

There’s another reason for its importance: as the name implies, magnetite is magnetic naturally. It can even become a permanent magnet if exposed to the right magnetic fields. This was an invaluable property for early humans and navigation. It’s thought that naturally occurring magnets formed from magnetite were how humans originally discovered magnetism.

The Lodestone

A naturally occurring magnetite magnet is generally called a lodestone. No one’s quite sure what happened to these stones to make them permanent magnets, only a very small percentage of the material naturally displays magnetism.

This material naturally attracted curiosity. There’s some evidence of Chinese compasses actually made from lodestone being used. These appear to have been used in geomantic divination, rather than as navigational tools. The so-called “South Pointing Fish” was developed, which was a wooden fish embedded with a needle magnetized by rubbing it on a lodestone.

These early examples show that it took humans quite a while to get a grasp on magnetism and its practical uses. These days, knowing much more about electromagnetic fields, magnetite is still a common subject to crop up.

Magnetite and Biomagnetism

One of the more curious properties of magnetite is that it’s found in many living creatures, including us. Biogenic crystals of magnetite are responsible for many of the biomagnetic phenomena seen in animals.

While it’s presence in the brain sounds really cool, the mineral isn’t good for you in too high of quantities. It also appears that we absorb some magnetite from pollution.

For instance, it appears that many birds carry magnetite crystals in the upper portion of their beaks which help with navigation.

In other cases, we’ve found minute fossils known as magnetofossils. These are the fossilized remains of bacteria that had previous biomagnetic properties, known as magnetotactic bacteria.

What Forms Does Magnetite Come In?

For the collector, the important thing is to sort out what kind of forms magnetite is found in. For the most part, they’re found as octahedral crystals which are often quite small and stacked together. In other cases, large, singular crystals are found.

Since magnetite is such a common mineral, it can also be found in places like black sand beaches.

Black Sand at Fort Funston
Black sand that consists of magnetite (credit: Nicki Dugan Pogue)
macro photograph of black sand magnetite
This detailed photo of black sand reveals the tiny pieces of magnetite that give it its distinctive black hue. (credit:  Richard Droker /Flickr)

Naturally occurring lodestone is a mixture of minerals, but of interest to many collectors. It doesn’t have the same form as magnetite crystals and is instead a simple grey-to-black stone. These are often unremarkable at first glance, and most displays I’ve seen have included a few paperclips or needles to make it readily apparent the stone is magnetic.

magnetite with paperclips

There is a very rare cubic form of magnetite, only found in a couple of places across the planet.

Large masses of magnetite are often found in banded iron formations. These are alternating layers of sedimentary chert and iron-rich minerals. These are most often seen with bands ranging from millimeters to a couple of centimeters in thickness.

While some of these can be formed into beautiful cabochons or other decorative uses, the majority of the material ends up being used as iron ore.

Rare cubic form of magnetite
Rare cubic form of magnetite

One thing to keep in mind is that magnetite is frequently found with other minerals. These samples tend to be worth more, especially if they feature well-formed crystals of more than one mineral. Magnetite crystals on their own tend to be quite cheap, although one should never underestimate the thrill of removing your own samples from the ground!

Where Can I Find Magnetite?

Magnetite is present in 49 of the 50 states in the Union. The only one that appears to not have any is North Dakota. Naturally, this means there are thousands of occurrences in the United States alone so it can be hard to pin down where to search.

Due to that fact, we’ll focus on the more extraordinary samples of the crystals found. 

magnetite specimen held in hand

The most interesting of those that occur in the United States are the crystals from St. Lawrence County, New York. Here is one of the very rare places where cubic magnetite crystals are found on a regular basis. It’s thought this has to do with the distribution of cations like zinc, but it hasn’t been definitively proven.

Speaking of New England, most of the area has magnetite to one degree or another. There are over a thousand known occurrences of the mineral in this region.

There’s considerably less in the central portion of the United States, from about Illinois to Texas, although it’s still present in many places in those states. North Dakota, as noted above, doesn’t actually seem to have any deposits of magnetite at all but the Southwestern portion of the United States is laden with it.

In most of the areas, I mentioned you’ll be able to find magnetite alongside whatever other local minerals are present. To what degree can be hard to say, since magnetite particles can vary so much.

The bottom line is that if you’re digging for minerals it’s a good idea to keep an eye out for magnetite crystals. 

Magnetite Specifications and Characteristics

ColorRich, metallic black or gray that can fade to dark brown shades
Crystal structureHexagonal
LusterMetallic to submetallic
TransparencyUsually opaque
Refractive index2.42
Density5.17-5.18
ClarityOpaque
CleavageImperfect/Fair
FractureNone, but sometimes exhibits parting
StreakBlack

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