Magnesioriebeckite

Magnesioriebeckite is a sodium-bearing amphibole mineral in the riebeckite series, the magnesium-rich counterpart of riebeckite. Crocidolite (blue asbestos) is the asbestiform variety of riebeckite, and some crocidolite and some fibrous amphiboles from other deposits, including Libby, Montana, have compositions that fall in the magnesioriebeckite range.

Origin

The name is formed from riebeckite, a mineral named for the German explorer Emil Riebeck, with the prefix magnesio- to show that magnesium takes the place of iron at key sites in the crystal. Its exact boundaries are set by the International Mineralogical Association's amphibole nomenclature, which has been revised several times; the hyphenated spelling magnesio-riebeckite is used in the current scheme.

Significance in Asbestos Context

Amphibole names are assigned by chemistry, so the same fibrous mineral can be called riebeckite, magnesioriebeckite or crocidolite depending on the analysis and the naming rules in use. This matters because several asbestos laws list only six named minerals: chrysotile, crocidolite, amosite, tremolite, actinolite and anthophyllite. When a fiber is reported as magnesioriebeckite rather than crocidolite, a defendant may argue that it is not regulated asbestos. U.S. Geological Survey work on the Libby amphiboles found mostly winchite and richterite, with smaller amounts of tremolite, magnesioriebeckite and other species, and these fibers are recognized as causing asbestos disease. For a patient, the label on a lab report is less important than whether the fibers were asbestiform and of a size that can be inhaled and retained.

Example Sentence

The microprobe data placed the blue amphibole fibers in the magnesioriebeckite field, which the plaintiff's mineralogist said was consistent with crocidolite.

Related Terms

Riebeckite, Crocidolite, Sodic Amphibole, amphibole nomenclature, International Mineralogical Association (IMA), Libby amphiboles, Electron Microprobe Analysis

Notes

• If a report names an unfamiliar amphibole, ask whether it was asbestiform and how it was identified.
• A fiber's name can change with newer naming rules; ask which nomenclature the lab used.