How to Identify Chert (5 Tips for Beginners)

Chert, also known as flint, is an all-purpose rock found in many different forms.

It can be found polished and tumbled for decorative purposes and jewelry.

It is also incredibly useful when it comes to construction, being a very common material in road surfacing and driveway construction thanks to its strength and resilience in all weather conditions.

How to Identify Chert (EXPLAINED)

What is Chert?

Chert is a sedimentary rock, mostly composed of silica.

It is formed in the sediment precursors of limestone and chalk, mostly produced on the ocean floor.

Microscopic organisms in the ocean have skeletons made of silica, which fall to the bottom of the ocean, dissolve, re-crystalize, and then petrify into chert.

Because of the petrification, it is often mistaken for fossils. Chert, in its darkly-colored form, is better known as flint.

Most people are aware of flint as being the stone that helps spark fire.

This is done by striking steel against it. In fact, a flintlock is a primitive firearm, where the gunpowder is ignited by a metal plate being struck by a flint hammer.

Additionally, because of its hardness, it is not only great for sharpening knives, but was also used by early humans to create weapons and tools, such as spears and knives.

This is because the broken edges of chert are naturally very sharp and retain their sharpness because of their durability.

How to Identify Chert

Since chert is such a common-looking stone, it can be tricky trying to identify it. Here are some really useful tips 

Look at the color

Chert can actually be found in a wide array of colors.

Different shades of grey are the most common, followed by cream colors to dark brown.

But, orange, yellow, green, and red are also naturally occurring.

Iron can produce the red color while mineral inclusions can cause the other colors.

If chert is red and opaque, it is called jasper, while a more translucent chert is known as agate.

The word “flint” is in reference to chert in the darker color spectrum.

So, when trying to identify chert, keep in mind that there are many colors in which these stones occur.

Identify the luster

In stone identification, luster refers to the amount of light the surface reflects.

The raw, unpolished stone has a surface that is rather dull, almost waxy-looking.

But, polished, it can have quite a nice luster, similar to tumbled tourmaline or garnet.

It is not a stone that can achieve the most brilliant luster, but it does give a nice shine.

Look for inclusions

Inclusions are color variations in a stone, usually due to different minerals and organic material mixed in while the stone was forming.

Chert is a very pure stone, almost completely silica, so inclusions are rare.

If you find a stone that has banding, veins, or color grading, chances are that it is not chert.

Even the colorful chert stones usually have one strong color.

Once in a while you might find a chert stone that has a small amount of color variation or veining, but it will be very subtle.

Check the hardness

The MOHS Hardness Test is a scale that helps you determine the hardness of stones.

It goes from one to ten, with one being the softest and ten being the hardest.

A stone that’s higher up on the scale is unable to be scratched by a material lower on the scale.

Chert is a seven, meaning that it is a very hard stone.

Luckily, it is relatively easy to do an MOHS test. First, you want to find another material that is lower than a seven on the scale, like a regular kitchen knife.

If the knife is able to produce a scratch, then it’s not chert, because a kitchen knife is lower on the scale.

Then, try something higher than a seven, like a drillbit.

Since this is higher up on the scale, it should produce a scratch.

So, if you find that your chert is unable to be scratched by a kitchen knife, but is scratched by a drillbit, then there’s a good chance that your stone is genuine.

See if it came from a nodule

If you are looking for chert in the wild, be aware that they often form in nodules.

A nodule is a lump of stone that is made of different matter than the stone it has formed on.

Since chert is almost one hundred percent silica, it usually has a different composition than the surrounding stone.

Chert is found commonly formed on limestone, and it stands out because it is harder than limestone, and therefore less prone to erosion.

That is why they form as hard knots on top of limestone.

Remember to be careful that what you have is genuine chert

Whatever reason you have chert, whether it’s for sparking a flame, for jewelry, or to sharpen knives, it is very important to ensure that you have true chert.

Since it is such a useful stone, be careful that you aren’t dealing with an imposter stone.

Remember that chert comes in such a variety of colors, so keep in mind that it is easy to mistake it for other stones.

Grey chalcedony is a common grey stone that is also opaque with few inclusions.

Red carnelian can be easily mistaken for red jasper, and green aventurine can look suspiciously like green chert.

Keep a keen eye out for all of these potential stone mix-ups.

Although it’s usually important to know how to properly take care of your stone, chert is a little different.

Because of its durability, it won’t disintegrate under water, scratch easily, or break, even if you throw it against a wall.

This is what makes it a great stone for decoration, jewelry, and gravel.

One of the most useful stones on the planet, chert is a lucky find for anybody.

Whether you are using it to spark a fire, repave your driveway, or wear around your neck, it is a great stone to have.

You might also like:

how to identify chert