Chert is most often created when microcrystals of silicon dioxide are formed within soft sediments that over time will turn into chalk or limestone. When large amounts of silicon dioxide microcrystals are present in the sediment, they start to clump together and can eventually form whole layers of chert within a limestone deposit.
Chert is a sedimentary rock that is comprised of silicon dioxide. It is usually found as big layers tucked into chalk or limestone. Because of chert's structure, when it is broken, it often breaks into pieces with extremely sharp edges. Early humans noticed this quality and used this type of rock to create cutting tools and weapons. Chert is also often referred to as "flint."
When microcrystals start to clump together within specific sediment deposits, they will eventually lead to the formation of chert. These deposits are under a ton of pressure and, over time, will compress into either limestone or chalk. Silicon dioxide crystals form within the sediment and get transported by groundwater. The crystals start to pack together and create a layer within the sediment, which eventually turns into a layer of chert mixed into the many layers of chalk or limestone. When the silicone dioxide does not form layers, chert is instead formed as irregularly shaped nodules within the limestone or chalk.