Flint and the Patination of Flint Artifacts

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Abstract
The alteration of black or dark-coloured flint artifacts to produce a white surface is familiar to archaeologists. This patination is attributed to weathering, and was first explained by Judd in 1887. Judd suggested that flint is composed of a felted aggregate of euhedral quartz needles with colloidal (opaline) silica occupying the interstices between the crystalline grains. He postulated that carbonate-bearing ground-water leached the more soluble amorphous silica, leaving minute interstitial cavities in the altered margin of the flint. The multitudes of surfaces thus produced reflect and refract light falling upon or passing through the flint, and the resulting scattering causes the white appearance of the altered portion. Judd cited the white aspect of powdered black obsidian as an example of such scattering effects.

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