Brownmillerite

Information about Brownmillerite

Brownmillerite is a calcium iron aluminium oxide mineral – a naturally occurring version of a compound that is far better known to materials scientists and cement chemists as a ubiquitous phase in Portland cement clinker than it is to mineral collectors.

It is a rare mineral in natural geological settings, known from a small number of localities in thermally metamorphosed rocks and volcanic environments, but the synthetic compound (which shares its crystal structure) is one of the most intensely studied phases in cement, ceramic, and solid oxide fuel cell research.

It forms dark brown to reddish-brown fibrous to prismatic crystals, typically small, with an orthorhombic crystal structure.

Uses and History

Brownmillerite itself has no direct industrial uses as a mineral – the compound is produced synthetically in large quantities as part of cement production without any reference to the natural mineral.

However, its crystal structure and the broader family of related perovskite-brownmillerite compounds are of major current research interest for solid oxide fuel cells, ionic conductors, and magnetic materials.

Mineralogy

Hazards and Warnings

No specific health risks have been formally recorded for brownmillerite as a mineral specimen. As with all calcium aluminate compounds, fine dust should not be inhaled.

Almost all rocks, minerals (and, frankly, almost all other substances on earth) can produce toxic dust when cutting, which can cause serious respiratory conditions including silicosis. When cutting or polishing rocks, minerals, shells, etc, all work should be done wet to minimise the dust, and a suitable respirator or extraction system should be used.

Translations

Further Reading / External Links

• https://en.wikipedia.org/wiki/Brownmillerite
• https://www.mindat.org/min-790.html
• https://www.handbookofmineralogy.org/pdfs/brownmillerite.pdf