zabargad -the ancient peridot island in the red sea.pdf

8/10/2019 Zabargad -The Ancient Peridot Island in The Red Sea.pdf

1/7

ZABARGAD:

THE ANCIENT PERIDOT ISLANDIN THE RED SEABy dward Giibelin

Ref lec ting o n h is 1980 visi t t Zabargad ,th e auth or provides 11ti upda te o n thi sr e l a ti v e l y u n k n o w n i s la n d a n d t h ebcarrt iful peridots for w hi ch i t has gainedfame. He con ~p lem en ts i s d i scuss ion ofthe geology of Z al? ag ad , the peridotoccur rences , the min ing techniques , andthe charac te r is t ics of the gemsto ne w i th al o o k u t t h e a l ~ c i e n t i s t o r y o f t h e is l a n dand the e tymologica l c liangcssur rounding th e s tone s cur rent nam e,p e ri do t. A lt h o u g h s o m e w h a t l o w o n t h eh a r dn e s s s ca le , t h i s n ~ a g n l f i c e n t e m s t o n ehas regained popufrrr appreciat ion, an d t hecrystals from Zabargud are st i l l arnolig th ef ines t in the wor ld .

BOUT THE UTHOR

Dr. Gubelin is a gernolog~st nd honoraryprofessor at the University of StellenboschSw~tzer land.

Acknowledgmenls: The author extends hisgenuine thanks to Professor Dr . Max We ibel ofthe lnstitute for Crystallography and Petrographyof the Univers~tyof Zurich for his reading of themanuscript a nd hrs helpful comm entary. Manyappreciative thanks also to Dr. P. Bancroft ofFallbrook Cal~fo rnia who arranged the excursionand was an excellent companion.

9 1 Gemological Institute of America

bargad is the oldest and longest- lznown sourceof gem peridots (fig. 1) ; yet the island, just as

mu ch as the gemstone i t hoarded , has s l id repea ted ly in toobl ivion, on ly to be rediscovered over and over again a ndforgo tten once more . Th e au th or v is it ed th i s t iny i s landi n the Red Sea i n March of 1980 . Loca ted about 6 0 mi lessou the ast of th e RBs Bands pen insula , at 23 36 ' 16Nand 36 11 ' 42 E (fig. 2) ) t is situated 16 lzm nor th of t heTrop ic of Can cer. Zabargad is only 3.2 lzm long and 2.4lzm wide, covering an area of 4.5 l zm2. The re i s h ard lyany l ife on the i s land an d no f resh wate r at a l l ; one mayjustly describe i t as a deser t is land. In fact , apart f romlow-growing shrubs , severa l g ian t tu r t l es , a nd a few b i rdssuc h as wagtai ls , ospreys, an d gul ls , pract ical ly n o f loraor fauna ex is t on Zabargad . Th e h ighes t g round i s the so-

cal led Perido t Hil l (235 m above sea level), whic h to-g e t h e r w i t h s o m e s m a l l e r h il l s 135 m above sea level)forms the m os t impressive s igh t tha t the i s land offers theapproaching seafarer ( f ig . 3) . Desp i te th e lack of vegeta-t ion , the i s land i s a t i t s mos t beau t i fu l whe n the ye l lowto dark brown toi les of th e various roclzs and du mp -heap sbefore the m an y p i t s b r igh ten in the l igh t of th e mo rn in gs u n . T h e a d v e n t u r e r w i t h a n y i m a g i n a t i o n a t a l l c a n n o tavoid le t t ing the pagea nt of his to ry unfold (s ee box) .

REGIONAL GEOLOGYT he o ccur rence of per ido t o n Zabargad i s in t imate lyrelated to th e regional geology an d th e tec tonic processes

tha t o n a l a rger sca le were respons ib le for the fo rmat ionof the Red Sea i tself. As a n extensio n of the East Afr icanRif t Val ley an d par t of th e global r i f t system , the Red Seais a geo log ica l ly young fea ture tha t evo lved in the T er-t iary period of geologic t ime, 6 5 to 13 mil l io n yea rs ago.

Th e rocks seen o n the i s land represent the resu l t s ofma gm atic act ivi ty with associated me tam orp hism ofpreex ist ing sed iments a nd were a l l exposed th rough tec -

Zabargad GEMS : GEMOLOGY pring 98


2/7

tonic uplift and erosion. Mafic igneous rocksBadgley, 1965), whic h represent the b ulk of the

island, are of deep-seated orig in. They a re notablefor their low silica content and consist prim arilyof lherzolites, characterized by abundant olivine,pyroxene, and amphibole. The metamorphicrocks, in turn , consist of serpentinites, granu-

lites, schists, and slates. The alluvial sedimentsand an extensive gypsum deposit are of morerecent origin.

T he topography of th e island reflects its tec-tonic history. Th e terrain is extremely irregular,the coastline consisting of fractured e scarpmentterraces. Numerous coral banlzs and reefs occurin the surrounding waters.

Zabargad

THE PERIDOTOCCURRENCESN o detailed documentation of th e peridot occur-rences on Zabargad has been made. An in ter-esti ng review of available inf orm atio n is providedby Wilson 1976).

It seems likely that peridots were once found

on seve ral pa rts of the island-in fact, alm os teverywhere the peridoti tes outcrop. The f inestand largest gem crystals, it is believed, occurredin su ch quan titites on th e eastern slopes of Per-idot Hil l that m inin g was worthwhile. Here theyappear to have been recovered i n ve in-like areasof the serpentinized peridotite. Th e tiny vein sru in al l directions so that in places they form

GEMS GEMO LOGY Spring 98


3/7

SITUATIONMAP

bR4s BandsLPort Berenice

ZABARGADr

Basalt dykes

Peridotite e .g . Iherzolite, dunite, etc.)

Metamorphic rocks e.g, serpentinite, etc.)

lluvium gravels, sand, etc.)Scale 1 10,000

-liocene coral reef & raised beach

0, m Gypsum

AT R I A N G U L AT I O NPT. FAULT3 6 O 1 2

RUINS O F HOUSES + HORIZONTALSTRATA

Figure 2 Geologic m a p o f the island of Zabargad Inset shows the relationship of theisland t o the Egyptian mainland

an actual stockwork that occupies an oval regionof considerable extent.

The peridot crystals mus t originally have fol-lowed and lined open cracks and fissures, inas-much as they were probably formed on the wallsof fractures. As a result of tectonic movemenfs,they were later broken from their original sitesand included among the rubble of the cracks. Inthis author s view, however, this theory is onlyvalid if the transformation of the peridotite intoserpent inite occurred metasomatically and beforeor during the formation of the peridot crystals;otherwise they too would have undergone serpen-tinization. Since the crystals are absolutely freshand well preserved, or at the most very slightly

etched, they must have developed at the sametime or at a later stage. However, unless and untilthe island is investigated in its entirety miner-alogically and petrographically, such ideas mustremain speculations.

Shortly before the visit of the author and hiscompanion, a joint American-Austrian expedi-tion consisting of curators from the ViennaMuseum of Natural History and the AmericanMuseum of Natural History in cooperation withthe Egyptian Geological Survey, and with thehelp of the El Nasr Phosphate Company, spentseveral days on the island. It is to be hoped thatnew and valid knowledge can be expected fromthese investigators. At the old sieving places (fig.

abargad G MS G MOLOGY Spring 198


4/7

merly, however, one could find peridot crystalsup to 10 cm long, although those 2-4 cm inlength were much more abundant. The Geolog-ical Museum in London owns a splendid step-cutperidot of 146 ct., while the largest known cutperidot weighs 310 ct. and is exhibited at theSmithsonian Institution in Washington, DC. Bothof these magnificent samples came originallyfrom the island of Zabargad.

MININGThe original mining methods consisted of prim-itive manual digging, whereby each individualvein w ~ xcavated fig. 5). The miners worlzed

Figure 4. Sieving place in the foreground anddump-heaps in the background on the easternslope of Peridot Hill.

4), i n the prematurely abandoned sieve-heaps,and among the waste of the mines, the authorand his companion found over a hundred fresh,transparent, well-preserved, in part broken butcertainly cutable peridot crystals pale yellowishgreen to deep olive green in color. Conspicuoussamples of the macroscopic paragenesis of theseperidot crystals were green garnierite and freshwhitish to weathered grey cancrinite. The peridot Figure 5 tunnel dug into metamorphiccrystals, pseudohexagonal after b 010) in form, rock to reach the deeper mafic rock note thewere between 5 and 15 mm along the a-axis. For- while bands of magnesite).

Zabargad G M S G M O L O G Y Spring 1981


5/7

FROM TOPAZOS TO PERIDOT:ZABARGAD AND ITS GEM S H A R E A PLACE

IN HISTORY L A N G U A G E , AND L O R E

Topazios is the name used by Greelz author Alexander Polyhistor to refer to an island onwhich gemstone s are found whose color resembles that of fresh oil. The great nat ura lis tof anc ien t times, Pliny the Elder (23-79 A.D.), men tio ns the island Topazios i n hi s workNaturalis Historia. He refers specifically t o Icing Juba I1 of Maure tania (2 5 B.C.-23 A.D.)who reportedly states in his writings that this legendary island in the Red Sea was firstexplored duri ng th e reign of Queen Berenice (340-279 B.C.]. Pliny als o refers to anot herreport that pirates driven by adverse winds landed on a n island i n the Red Sea called Chytisor Cytis. Being in a famished condition, they sought herbs and roots in the ground andthereby fouild the first topazos. Other names attributed to the island in ancient timesinclud e Island of Deat h (Nelzron ) and Ophiodes ( snalze island, reported by Agatharchidesof Knidos, 18 1 146 B.C.). Not until the t im e of th e Crusades did this myster y-bound scrapof land receive t he n am e by which it i s still mistalzenly lznown in th e West, St. John'sIsland, and finally, Zabargad.

For Pli ny the Elder, topazos was a jewel that ma inly oc curs i n green but may also be yellow.Probably there is some confusion here with chrysolite, chrysolithos, which was alsolznown in ancient times (Ezelziel 10, 9). Du ri ng the period, chrysos meant golden, that is,yellow. Not until muc h later did the word experience a n etyn~ olog ica l hange as the prefixchryso- entered com mon usage t o describe a green sto ne (see chrysoberyl, chrysoprase ,chr ysopal, chr ysocolla, chrysolite, etc.

When in the early 18th century the name topoz was finally affixed to the fluorine- bearin galuminum silicate that currently holds this title, a new name was needed for the greengemstone from Zabargad. In 1790, the sometime mineralogist A. G. Werner nained themin era l oli vine because of it s typical olive-green color. In the sa me year, he published adescription of chry solite in Bergmanns /ournu1 3 stating that it was a mineral i n it s ownright. A few years later, M . H. Klaproth was able to prove th at olivine and chrysolite belongto th e sa me family of minera ls. Although chrysol i te was used by German and American~n in er al ogi st s or over 100 years, thi s te rm ha s left general usage and is no longer acceptedin English nomenclat ure for th e gemstone. The English adopted Werner's nam e ol iv inewhile th e French gave preference to the new nam e peridot which i s derived from t he Ara-bian word furidat meanin g gem. The latte r is generally used today t o refer to t he gemstone,whereas the true nam e of the minera l is olivine (see Ball, 1950, Liischen, 1979, and Mitche l,1979, for fur the r information on the various nam es).

Archaeological excavations in Alexandria have apparently unearthed valuable peridots.Faceted samples, which could only have come from Zabargad, have also been discoveredin ancien t Greece. In al l probability, the fabulous stone that once adorned King Ezelzielfro m T yru s ( abo ut 586 B.C.; Ezelziel 28, 13) was a peridot fr om Zabargad. Where so mu chtreasure and beauty were to be found, the authorities kept a wary eye. Diodorus Siculuswrite s in the first century before Christ : The Egyptians Izept the island under constant

watch, and anyone who tried to approach the treasure island without permission-letalone to attem pt to land and ste al the peridots-was threatened with death. Thus, thisislan d i n the Red Sea became one of the mo st closely guarded regions of the an cie nt world,and its treasure was held secret for centuries, virtually hidden from the Western worldfrom biblical times until the onset of the baroque period i n the 17th centur y.

Zabargad GEMS k GEMOLOGY Spring 1981


6/7

Figure 6 Peridot crystal oni t s original matrix self-collected b y t h e author.T h e crystal i s approxi-

m a t e l y 1 2 cm 1.1 c m .

downwards unti l the vein, usually at a shallowdepth, became sterile or contracted. However, theperidots were not found where they had crystal-lized. They were always loosely attached to thewa lls of the veinlets an d could easily be removedfrom their position. Wilson (1976) noted that hekn ew of no peridot crystal that he could in goodconscience claim w as found directly grown on itsmo ther-ro ck. However, t he auth or of thi s presentartic le was so lucky as to find a piece of matrixabou t the size of a child's f ist wi th a fully grown,well-developed peridot cry stal attach ed (fig. 6).

During the years before World War I, fromabout 1906 onwards, th e island of Zabargad w asgenerally lznown asthe sou rce of peridot, an dm inin g rights were monopolized by the Khedive,the Tu rkis h viceroy i n Egypt. W ithin a four-yearperiod, more than $2 mill ion in peridot (presentday value ) was found a nd sent to France for cut -ting. The chief problem on the island then, asnow, w as the lack of fresh drink ing water for theminers . The m ining company overcame this d i f -ficulty by erecting a large gasoline-powered watercondenser (of which a few ru sty p arts .are stilllying aroun d today). In 1922 the Egyptian govern-ment gave the mining rights to the Red SeaMining Company. In the years that followed,un til th e outb reak of W orld War 11, thi s com pan ybrought o ut a considerable am ou nt of peridot. In1958, the d eposits were nationalized by EgyptianPresident G A . Nasser.

DESCRIPTION ANDPROPERTIESGem peridot lies compositionally between theend m embers forsterite (M gzSi0 4) nd fay ali te(Fe,SiO,) of the olivine isomorphous series (Mg,Fe),[SiO,], i n w hich the two divalent cationsMg and Fe can replace each other diadochally.The peridots from Zabargad contain 8%-10%FeO (FeO MgO am oun t to approximately 64%;Wilson, 1976). Th e c rystals ar e elongated alongthe a-axis so that the brachy pinacoid b(010),which is markedly str iated vertically to thec-axis, forms the largest face. The gradations incolor of this summer-green gemstone (the birth-stone for August) , as well as the variations i n i tsother physical properties, are caused by the ironcontent (see Troeger, 1956, p. 54) and other com -ponents. The color tones of t he fin es t qualitie scorrespond with the DIN color chart 6164, page24, colors 24:6:2;2 4:6:3 to 24 :6:4 of th e colorno rm s X c34.2; YC43.7; Z,10.2 or X c23.0; Y,29.4;Zc6.9 or Xc15.2; Y 19.5, and Zc4.6. Refractiveindices vary little, from 1.650 to 1.654 for n a a ndbetween 1.686 and 1.690 for ny, with a cons tantvalue for np only a little below the m iddle of thetwo extreme readings. The high birefringenceremains constant at 0.036, as does the density(3.34)wh ich is only 0.01 above that of p ure m eth -ylene iodide, i n which liquid peridot rema ins sus-pended or sin ks slowly. Pleochroism is weak bu tperceptible as pale green alongcu green alongP

Zabargad GEMS GEMOLOGY Spring 98


7/7

zabargad -the ancient peridot island in the red sea.pdf

Documents