Feature Gems & Gemology, Spring 2011, Volume 47, No. 1

Demantoid and Topazolite from Antetezambato, Northern Madagascar: Review and New Data

An important deposit of andradite, containing demantoid and topazolite varieties, has been mined near the village of Antetezambato in northern Madagascar since early 2009. Most of the activity took place from April through November 2009, and yielded a large quantity of rough material in a wide range of colors. The deposit has a skarn origin, related to contact metamorphism between Cenozoic magmatic intrusions and Mesozoic calcareous sediments. The garnets’ internal features consist mainly of fluid inclusions, fractures, wollastonite needles (or their remnant channels), and diopside aggregates. The chemical composition is close to pure andradite, with negligible Cr and V contents; thus, iron is likely the main chromophore. LA-ICP-MS analysis showed a relatively high content of light rare-earth elements.


Rare-Earth Element Composition 
May 2, 2011