Volume 21, Number 3
Sep 1997

Balls of Pyrite Crystals Found Growing in Old Books

Every few years, the journal Science, or its English counterpart Nature, runs a story from the world of books or conservation. One of them reported the metals found in Gutenberg's inks; another described the then-new process of cleaning artifacts with lasers; and now the Nature issue of August 14 has a story entitled "Framboidal Pyrites in Antique Books," on p. 631.

A framboid is a spheroidal aggregate of microcrystals. It has a diameter of up to 150 �m (microns, now called micrometers). This is on the scale of a dust particle, less than 150 millionths of a meter in diameter. Pyrite (iron sulphide) crystals are less than one �m in diameter.

What made this a story is not the rarity of framboidal pyrites, because they are found in a variety of places, including hydrothermal veins and sedimentary rocks, but the fact that they grew from scratch within sixteenth and seventeenth century books. In other words, tiny rocks have been found growing in old books. They were found in a black powder in the books' gutters, and were made at least partly from iron-gall ink components: tannin, gum arabic, iron salts, additives and solvents. The SEM micrograph shows them to be nearly perfect spheroids with fairly smooth surfaces.

The old books had provided nearly perfect growth conditions: long periods without disturbance in intermittent oxic-anoxic conditions.

This work was done by Javier Garcia-Guinea and other scientists from the Museo Nacional de Ciencias Naturales and the Archivo Histórico Nacional in Madrid. They say that their discovery "supports the recently published hypothesis that the formation of framboidal pyrites does not require a narrow set of physical or chemical conditions."

[The Nature article was sent in by Joan Batchelor of Washington, DC.]