Kremen

Flint occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones. Inside the nodule, flint is usually dark grey or black, green, white, or brown in colour, and has a glassy or waxy appearance. Historically, flint was used to make stone tools and start fires.

Origin and Formation

Chert is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO₂). Where chert occurs in chalk or marl, it is usually called flint. Most cherts are nearly pure silica, with less than 5% of other minerals. Most chert nodules have textures suggesting they were formed by diagenetic replacement, where silica was deposited in place of calcium carbonate or clay minerals. Certain types of flint, such as that from the south coast of England and its counterpart on the French side of the Channel, contain trapped fossilised marine flora.

Chemistry

Silicon dioxide is a relatively inert material, hence its widespread occurrence as a mineral. Alpha quartz is the most stable form of solid SiO₂ at room temperature.

Fire and Tools

The use of flint to make stone tools dates back more than three million years. Flint is one of the primary materials used to define the Stone Age. Flint Ridge in Ohio was an important source of flint, and Native Americans extracted flint from hundreds of quarries along the ridge. To make flint easier to work, it can be heat-treated by bringing it slowly to between 150 and 260 °C for 24 hours and then cooling it slowly; above that range it tends to explode. When struck against steel, flint will produce enough sparks to ignite a fire with the correct tinder, or gunpowder used in weapons, namely the flintlock firing mechanism. In the 20th century, flint and steel were superseded for striking sparks by ferrocerium. Ötzi, a well-preserved natural mummy of a man who lived in the Ötztal Alps between 3400 and 3100 BCE, carried tinder fungus along with flint and pyrite for creating sparks.

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