Feature Gems & Gemology, Winter 2011, Volume 47, No. 4

Determining Garnet Composition from Magnetic Susceptibility and Other Properties

Quantitative measurements of magnetic susceptibility combined with RI or SG data can provide an easy and inexpensive way of inferring garnet composition. At the time this technique was first applied to faceted garnets (Hoover et al., 2008), a reference set of samples with well-characterized compositions was not available. GIA subsequently provided 28 garnets and their chemical data determined by electron microprobe for a comparison with end-member compositions calculated from magnetic susceptibility measurements and other properties. The results show that endmember compositions based on microprobe data have error margins similar to most of those derived from directly measured properties.