What is this close-up picture? (WotsThat: Flint fracture surface)

Question

What object is shown in this zoomed-in close-up photo?

MarbleGhost · Accepted Answer

Flint fracture surface. When flint breaks, it creates razor-sharp edges that are actually sharper than modern surgical steel, which is why prehistoric humans preferred it over other stones for tools and why some surgeons today still use obsidian blades (which fracture similarly) for the most delicate operations. The curved, ripple-like patterns you see on a broken flint surface, called conchoidal fractures, form because flint is so uniformly dense that stress waves spread outward in perfect circles—almost like throwing a stone in still water.

Answer: Flint fracture surface

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