Chert

Chert – A dense hard sedimentary rock rich in silica, with a sharp-edged, shell-like fracture, made up of microcrystalline and cryptocrystalline quartz. Throughout history, it was commonly used to make stone tools and start fires.

Obsidian or volcanic glass – A volcanic rock primarily composed of silicon dioxide (SiO2), formed by the rapid cooling of acidic lava, during which crystals did not form. In human history, it was highly valued because tools, blades, and arrowheads could be made from it, and it could also be polished, allowing it to be used for early mirrors. Obsidian blades can reach molecular thinness, which is why they are still used as scalpel blades in surgery, as obsidian scalpels are sharper than the finest steels.

Quartzite – A metamorphic rock primarily composed of quartz, known for its exceptionally great hardness. Its interwoven structure and composition make it a durable and tough rock. It is so solid that it fractures through the quartz grains rather than along the boundaries between them. This characteristic distinguishes quartzite from other rocks with similar composition, such as quartz sandstones. Its conchoidal fracture allowed it to be shaped into large cutting tools like axe heads and scrapers, but its rough texture makes it less suitable for making tools with fine edges, such as knife blades.