How Flint is Formed

Flint, a type of rock found in or near deposits of chalk, was formed between 60 and 95 million years ago by accumulating deposits of silica (silicon dioxide) in oceans.  These deposits resulted from the deaths of trillions of sea creatures whose bodies contained silica, and the subsequent deposit of that material on the ocean floor.  “The majority of silica found in flint nodules is biogenic (produced by living organisms or biological processes).”

References to chalk point to the large accretions of calcium carbonate that resulted from the deaths of sea creatures with shells made largely of that material.  Most of these creatures were microscopic, and the sediment formed when their shells precipitated to the ocean floor formed that white material known today as chalk.

Some of the common names for this material

“Flint” is a familiar name for a particular part of the quartz family.  This mineral or rock, for there are those who refer to it as a member of both camps,  was used in antiquity for the hand manufacture of cutting tools, arrowheads, and spear tips.  Some authors, commenting on different grades of this rock, call it “chert,” but it is evident that there are no firm rules that explain the parameters for such differentiation.  “Firestone, Hornstone, and Silex are other names for flint and chert.”

How it came to be the way it is

Like most physical processes in nature, the conditions that allowed the formation of flint also resulted in many other silicates than the flints and cherts in focus here.  Some are classified as macrocrystalline (large crystals):  amethyst, rose quartz and smoky quartz.  Others display no obvious crystalline character, even under a microscope, and thus are called cyptocrystalline (crystals too small even for microscopy):  bloodstone, jasper and sard.  By no means does this list exhaust the varieties of quartz found on this planet: “This variety comes about because of the abundance and widespread distribution of quartz.”

Science looks for answers to questions, and the physical characteristics of the various quartzes raised those.  Analysis of the two main classes named above yields two subclasses into which cryptocrystalline quartzes naturally separate.  Chalcedony displays a parallel, fibrous structure, and this subclass contains agate, aventurine, bloodstone, carnelian, chrysoprase, onyx and sard.  When these materials are broken, they break raggedly, usually displaying thick and uneven edge features.

Chert, flint and jasper, on the other hand, are prone to breakage in a conchoidal (that is, smoothly rounded like an arch) pattern, frequently displaying a thin, sometimes razor-sharp edge.  These materials, upon microscopic examination, show a fine granular structure easily distinguishable from their fibrous relatives above.

Examination and display continue

Today’s uses for flint are less utilitarian than artistic; many people collect different samples of flint for display in galleries and for use in recreations of ancient conditions for educational purposes.  Until the midpoint of  the nineteenth century, flint was used in firearms to ignite the gunpowder charge and propel bullets toward their targets.  As noted previously, ancient peoples made wide use of flint in weapons and other tools that required its conchoidal fracture property to produce sharp edges.

Nevertheless, flint, chert and other examples of quartz’s many faces continue to be studied in order to understand how and where they were formed.  Flint is very common, and the possibility always exists that additional uses could be found for this versatile material.