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Main peridotite hill on Seberged Island

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Forsterite - Forsterit - Forsterite - Forsterita

Africa : Egypt : Red Sea : Peridote (Olivine) crystals up to > 1 m size in mantle diapirs on Seberged (also called : Zabargad, Zebirget, St. Johns or Topazios) Island

Coordinates : 23°36'N , 36°11'E : Seberged (Zabargad) Island, Red Sea, Egypt

Seberged is an island off the coast of Southern Egypt and though its only small, it is a very interesting place in terms of history, geology and biology. In recent times it is well known among divers, which come here to experience the thrill of a "bottomless" reef face at the outer margin of the island. But Seberged has much more to offer.

The Red Sea is a prime example for the tectonic breaking up of continents, resulting in a long and narrow ocean. But despite the predominant extension tectonics involved in the process of a continental break up, we often get also - apparently paradoxically - compressional elements of tectonics in these zones. In the case of Seberged the compression was extremely strong and resulted in a massive upthrusting of mantle material to the surface of the earth and in the formation of two islands : Seberged and neighbouring Shark Island in the ocean.

Hence the island of Seberged has a very complex geology with large slabs of mantle derived rocks, consisting predominantly of fresh peridotites, which may form lustrous green gemmy crystals up to 10 cm and more. The ancient egypts and greeks knew about these peridote crystals, and mined them for many centuries and the island became famous under the name of 'Topazios' in the ancient world. Later in christian times the name changed to 'St. Johns Island' before the island became forgotten for many a century.

The small island of Seberged was rediscovered in the 19th century, when geologists explored the old mines and found interesting nickel deposits, which were later mined in the Nasser era around 1960. Later the diving community discovered Seberged and the beautiful reefs around the island, steeply rising 500 m out of the oceans depth. And the modern geologist became aware of the unique geology on the island which allow a rare opportunity to investigate fresh and unweathered mantle derived rocks.

I had the privilege to have a short visit to remote Seberged in 1994. We visited the remains of the ancient mines and admired the beauty of the turquoise lagoon surrounding the island. Of course we also looked for peridote. We found some small gemmy crystals, mere leftovers of century long mining, but we also saw large - unfortunately not gemmy - olivine crystals embedded in peridotite rock with about 1 m size. The crystals are typical "olive" green and display a prismatic habitus. They seldom show idiomorphic crystal faces, but are clearly individual crystals of remarkable dimensions. Pitty, that I didnt took any photos of the crystals...

Update March 2007 : In our library you find a new link to an expedition report to Seberged in 1980, written by Peter Bancroft and published 1984 in his famous book "Gem & Crystal Treasures". Please click here for the report.


Seberged Island in a nutshell :

Mineralogy :

Olivine / Peridote / Forsterite

Crystal Size :

up to 1 m or maybe larger

Geology & Origin :

several upthrusted blocks of upper mantle peridotite, fresh and not serpentinized, embedded into a complex faulted metamorphic sequence. The peridote crystallized in situ in the upper mantle region

Current status :    

Seberged Island is generally not acessible and regarded as military zone. However the offshore grounds around the island provide very popular diving grounds.

Remarks :

The island presents an interesting opportunity to study fresh upper mantle rocks and their related mineralogy


 Other notable & famous forsterite occurences :

Note : Generally speaking, peridotites are slabs of upper earth mantle, which have been tectonically obducted onto or squeezed into other rocks of crustal origin are not exceedingly rare, hence rock forming peridote = olivine is a ratner common mineral at earth's surface. Exceptional crystals of peridote / forsterite however are scarce.

- In the last years many fine specimen of splendid peridote crystals reached the mineral fairs from the Kohistan area, Pakistan.

- Countless are the occurences of the basalt associated olivine / peridote nodules, where peridote form roundish, often gemmy crystals up to about 1 cm size. Just to name a few : Dreiser Weiher, Eifel, Germany; Peridot Mesa, San Carlos, Arizona, USA and Lanzarote Island, Canaries, Spain



Seberged Ahoy - first glimpse of the island and its peridotite hills

Photo : lms_namaste on


View of the central peridote hill with light brown reef and turquoise lagoon in forefront.

Photo : Photo : lms_namaste on


Dive grounds along the "bottomless abyss" - a reef cliff going straight down for 500 m

Photo : Photo : lms_namaste on



Resources and relevant weblinks :

For more information on the mineral forsterite please look at, Webmineral and the german Mineralienatlas.

As Seberged is one of the very few places to study fresh upper mantle derived rocks, there is a lot of modern geological literature about this island. Furthermore there are some good papers about the mineralogy of the gem peridote from Seberged. However to my knowledge none of the mentioned papers cover the existence of large peridote crystals on the island in any great detail.




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