How long does it take a pyrite framboid to form?

Abstract

Framboids are defined as microscopic, sub-spheroidal clusters of equant and equidimensional microcrystals. The microcrystals are usually constituted of pyrite and framboidal pyrite is one of the most abundant mineral textures in the natural environment. They are of particular interest to geochemists, sedimentologists, paleobiologists and materials scientists because of their potential paleoenvironmental significance, their widespread involvement in fossilization and their potential for the manufacture of self-organizing materials. Here I use a simple diffusion-nucleation model to compute framboid formation times. The results show that pyrite framboids take between 3 h and 3 yr to form depending on framboid size. The time taken for the average sedimentary framboid to form is about 5 days and the average syngenetic framboid forms within 3 days. The shorter formation times for syngenetic compared with diagenetic framboids helps explain the smaller size relative size distributions of syngenetic framboids. This has led to the use of framboid size-frequency measurements as proxies for ancient euxinia. The relatively rapid formation of pyrite framboids explains how pyrite infills and preserves soft tissues before cell lysis and before deformation through burial has been initiated. One unexpected consequence of the model is that it further explains how commonly observed groups of framboids can form contemporaneously.