You have 99 problems and Chert isn’t one of them. This relatively common rock is found worldwide and it comes in limitless colors and varieties. Despite the stone’s popularity, there are many misconceptions about Chert.
Chert is a sedimentary rock comprised of microcrystalline Quartz which makes it fairly hard, 7 on the Mohs Hardness Scale. It exhibits conchoidal fracturing and you’ll typically see colors ranging from brown, gray, green, or red. To make it more confusing you’ll need to know the many subvarieties of Chert, including Flint, Onyx, Agate, and Jasper.
What Is Chert?
Chert is a sedimentary rock composed of microcrystalline Quartz or cryptocrystalline Quartz, which is the mineral form of Silicone Dioxide. Chert occurs as concretionary masses, nodules, and layered deposits. If you’re wondering what the layered deposits look like then keep scrolling to see some great examples.
While Chert and Flint are often used interchangeably, they’re not the same. However, both are varieties of Chalcedony.
When this stone breaks it will show a conchoidal fracture, often producing incredibly sharp edges. Because of this, primitive people took advantage of how the stone broke and used them to fashion weapons and cutting tools.
Continuous color gradients exist between white and black or cream and brown. Green, yellow, red, and orange Chert are common. The darker colors are often the result of inclusions of organic and mineral matter.
When there is abundant Iron oxide in the ground, Chert can produce red hues. When these deep red colors are created by Mother Nature, rockhounds love collecting them but give them a different name, Red Jasper.
How To Identify Chert In The Field
In most cases, Chert is relatively easy to recognize when you know what you’re looking for.
The stone usually contains a waxy luster, with the conchoidal fracturing and sharp edges mentioned earlier. All Chert is incredibly hard and will not be scratched by steel. While some varieties are opaque, others are translucent.
Conchoidal fracturing is an excellent characteristic to look for when trying to identify Chert in the field. When broken, it will appear as though someone has scooped out a portion of the rock with a spoon. This results in smooth, convex depressions on the rock’s surface with sharp edges.
It’s possible that your specimen doesn’t display conchoidal fracturing. However, there are other rock types, like Obsidian, that fracture conchoidally, which is why additional testing and observation are helpful.
A hardness test is one of the best ways to identify Chert. The stone is exceptionally hard because it’s almost entirely made of Quartz. Remember to bring a steel nail with you before you head out into the field. You can use a steel nail to try to scratch the specimen. If the nail doesn’t leave a scratch, there’s a good possibility that it is, indeed, Chert.
Where Is Chert Found?
Some of the US states where common Chert is easily found include Pennsylvania, Missouri, and Florida. It’s often discovered interbedded with Limestone and Shale. Areas with a rich history of volcanic activity result in Chert formations. Other typical environments Chert can be found are gravels, mines, quarries, beaches, road cuts, streams, creek beds, and exposures.
Because Chert is a relatively common rock, pits, quarries, and mines are some of the best places to find it.
Tiny silica fossils significantly contribute to Chert’s formation. This is especially so for those at the bottom of the ocean. This is why beaches are also among the best environments to find specimens. Creeks, gravels, washes, draws, and streams are also significant areas to find various types of Chert, not just common Chert.
Outcrops, road cuts, or exposures are a few other incredible mediums to discover these rocks. Suppose you ever come across a limestone exposure. In that case, you’re almost guaranteed to find Chert specimens in the mix since it forms in these areas as nodules.
How Is Chert Formed?
Chert rocks are formed in various ways. However, the most common method occurs through biochemical means. Marine plankton siliceous skeletons dissolve during a process called “diagenesis.” As the silica precipitates from the process, Chert rocks are created.
Is Chert Valuable?
Chert is such a common and easily obtained stone that it’s not usually particularly valuable. However, it can be fashioned into incredible jewelry and makes beautiful decorative pieces. In the hands of a skilled crafter, it can be carved.
Consider this; it’s not uncommon to see hauled prices for Chert ranging from $10 to $15 per ton in many parts of the United States. That said, selling prices for smaller specimens aren’t going to fetch much of a high price.
Cherts can be characterized as having a fine-grained texture and a microcrystalline structure. This means that the stones are made of tiny mineral particles, making them feel soft to the touch.
While Chert can come in various colors, the streak it produces is white or very lightly colored.