The Origin of Flint

Abstract

WITH reference to Sir F. Ray Lankester's interesting notes on “The Origin of Flint” in NATURE of June 7, it is worthy of remark that the structure of black flints, referred to as consisting of minute crystals of silica embedded in colloici silica, may indicate the formation of such flints from the gradual crystallisation of silicic acid gels. Many cases of the production of micro-crystals in artificial inorganic and organic gels are known; indeed, these usually break up eventually with the development of such micro- or macrocrystals. The very slow crystallisation of gelatinous silica appears to be due largely to its small diffusion constant and insolubility.