Madagascar: A Gemologist’s Journey (Geological Overview)

Madagascar: A Gemologist's JourneyI recently took a trip to Madagascar for a mineralogy conference and to tour some of the remote mining villages. It was such a wonderful trip and I learned so much that I’d like to share my experience with you over the next couple of weeks.

Before I begin specifics about our journey, I’d like to touch on the geology of Madagascar. Madagascar has a very unique geological history, which created many unusual mineral deposits.

Roughly 2.5 billion years ago several land masses, including Madagascar, collided to form the Gondwana Supercontinent. The magmatism and metamorphism generated by this collision is largely in part responsible for Madagascar’s wealth of gemstone and mineral deposits.

Madagascar is divided into 3 geographical zones clearly visible on the image below:
1: Low Plains in the west comprised of Mesozoic to Cenozoic sediments
2: Central Highlands comprised of old crystalline basement complex
3: Narrow Coastal Strip in the east comprised of lower Cretaceous volcanics

Madagascar Topography

Madagascar has more mineral deposits than any other island in the world. It is especially rich in pegmatite deposits. More gems are found in pegmatite deposits around the world than any other type of deposit. Pegmatites form in granite and when conditions are perfect, can form gem pockets.

The overlay below shows all the major pegmatite districts in Madagascar, taken from the book Madagascar, by Federico Pezzotta. As you can see, most are located in the central highlands. This is where we spent the majority of our time.

Madagascar Topography
Madagascar Book For more information on the geology and mineralogy of Madagascar I suggest this book written by Federico Pezzota. The book is full of amazing photographs of beautiful gem and mineral specimens along with a wealth of information about Madagascar’s mineral localities. The book is $35 and $13 of each purchase goes to helping the kids in the remote mining villages of Madagascar. Contact me if you wish to order a book…it is almost out of print and I have fewer than 10 copies left: 970-535-4139.

In my next post I will begin our journey of Madagascar.

Author: Michelle M. Rahm is a GIA-trained Graduate Gemologist and is President of Colorado’s Mile High Chapter of the GIA Alumni Association. She has been selling gemstones and jewelry online since 1997. Visit her websites JewelryImpressions.com and OurCustomWeddingRings.com

About mrahm

Michelle holds a Graduate Gemologist Diploma, Graduate Diamonds Diploma and Graduate Colored Stones Diploma through the Gemological Institute of America's distance education program. Michelle currently serves as President of the Mile High GIA Alumni Association. She also serves on the board of the Rocky Mountain Jeweler's Association and is a member of the American Gem Trade Association.
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