Emerald, a green transparent variety of beryl, was one of
the most highly prized gemstones in antiquity. The earliest
known emerald mine
is located in the mountain valley of Wadi
Sikait in Egypt's Eastern Desert, where mining probably
began toward the end of the Ptolemaic period in the first
century BC.
Most of the mining activity, however, dates to
the Roman and Byzantine periods, from the late first century
BC through the sixth century AD.
The Romans referred to
emerald as smaragdus
and named the Sikait region Mons
Smaragdus or Emerald Mountain.
An archaeological geology survey of Wadi Sikait was
undertaken for the purpose of mapping the distribution of
ancient mine workings,
deducing
the ancient mining methods, and describing the geological
occurrence of emerald. It was found that emerald and other
green beryls occur within the contact zone between
phlogopite schist and intrusive quartz and pegmatite veins.
The workings, which were excavated in the softer phlogopite
schist with flat-edged chisels and pointed picks, are mostly
shallow, open-cut trenches that follow the quartz/ pegmatite veins. Some
workings continue as much as 100 m underground and are still
largely unexplored. It is noteworthy that the geological
occurrence of beryl in Wadi Sikait, the world's
oldest emerald mine
is essentially the same as for the world's newest emerald
discovery at Regal Ridge in Canada's Yukon Territory.
The study of ancient quarries and mines lies at the
interface of geology and archaeology. It is one aspect of
the broader discipline of 'archaeological geology' or, as it
is also known, 'geoarchaeology' (Herz and Garrison, 1998;
Rapp and Hill, 1998). Simply defined, archaeological geology
is the application of geological principles and methods to
archaeological objects and sites. In ancient Egypt, as with
most other early civilizations, much of what remains
consists of stone. There are building stones for temples and
pyramids; ornamental stones for vessels, stelae, sarcophagi,
statues and other sculptures; and precious stones for
jewelry. The archaeological geologist may investigate not
only the petrology and uses of these stones, but also the
quarries and mines that supplied them, including their
layout and operation, extraction and transport technologies,
and geologic setting. For Egypt, the study of archaeological
stones is well advanced (e.g., Aston et al., 2000; for
further information on the quarries and mines see the
author's web site at http:// www.eeescience.utoledo.edu/egypt/).
As an example of the application of archaeological geology,
the present paper looks at emerald mining in ancient Egypt.
This review also serves to provide a historical perspective
on Canada's own emerald deposit on Regal Ridge in the Pelly
Mountain range (near Finlayson Lake) of southeast Yukon
Territory. Emeralds were discovered here in 1998 on land
owned by Expatriate Resources Ltd. of Vancouver, BC and the
property is now being developed by True North
Gems Inc.,
also of Vancouver (Groat et al., 2002). Regal Ridge is the
world's youngest emerald discovery, but the world's first
emerald mine was in Egypt's Wadi Sikait (Fig. 1, 2). The
word 'wadi' means 'valley' in Arabic and 'Sikait' is a
Bedouin corruption of the ancient name for the site, 'Senskete'
or 'Senskis.'
Egypt was probably the only source of emerald and other
green beryl for the ancient civilizations of Europe and the
Mediterranean region. Although it has been suggested that
the emerald deposit at Habachtal near Salzburg, Austria was
worked as early as the Roman period, there is no conclusive
evidence that it was known prior to the Middle Ages (Sinkankas,
1981, p. 371-77). However, Giuliani et al. (1998, 2000) have
shown that the green beryls from Egypt and Austria are
distinguishable by their oxygen-isotopic composition, and
such testing, if applied to Roman jewelry, may yet reveal
Habachtal's true historical significance.
Egyptian emerald mining occurred not only in Wadi Sikait but
also at several other sites within 15 km of this valley,
including Gebel Zabara to the northwest, Wadi Nugrus and
Wadi Abu Rusheid to the west, Wadi Umm Kabu and Wadi Umm
Debaa to the southeast, and Wadi Gimal to the southwest.
Mining began first in Wadi Sikait sometime during the
Ptolemaic period (late 4th through mid-1st centuries BC)
with most of the activity occurring in the subsequent Roman
(late 1st century BC through 4th century AD) and Early
Byzantine (5th through early 6th centuries AD) periods. All
the other mining sites are strictly Roman-Byzantine or
Islamic (mid-6th century AD onward) in date. Beryl mining
ceased in Egypt with Spain's discovery of superior-quality
Colombian emeralds in the 16th century AD. It is commonly
reported in the literature (e.g., Giuliani et al., 2000, p.
631) that emeralds were used in Egypt as early as the 18th
dynasty (16th through 14th centuries BC) of the New Kingdom.
This claim, however, is based on the misidentification by
archaeologists of amazonite (a green variety of microcline)
as emerald (Lucas and Harris, 1962, p. 389-390). The
earliest unequivocal evidence for emerald mining in Egypt
dates to Ptolemaic times, and even for this period the
evidence is scant. It was the Romans who were primarily
responsible for developing the mines, and it was they who
gave the mining district its ancient name, Mons Smaragdus or
'Emerald Mountain'.
Emerald and other
Beryls
Beryl is a beryllium alumino-silicate mineral with the
chemical formula [Be.sub.3][Al.sub.2]([Si.sub.6][O.sub.18]).
Ordinary beryl is colourless but the presence of various
trace impurities gives the gemstone varieties of this
mineral their distinctive colours: green emerald, blue to
bluish-green aquamarine, pink morganite, red bixbite, and
yellow to yellowish-orange heliodor (Sinkankas, 1981, p.
206-235). Beryl almost always occurs as elongated crystals
with a hexagonal cross-section. It has a Mohs scratch
hardness of 7.5-8, which is exceeded by only a few other
gemstones such as chrysoberyl at 8.5, ruby and sapphire
corundum at 9, and diamond at 10. Although highly resistant
to grinding and cutting, beryl does have a weakly developed
basal cleavage. Ancient stonecutters could thus cleave it
perpendicular to the crystal axis to produce hexagonal
prisms of any desired length.
The name 'beryl' comes from the Roman naturalist Pliny the
Elder who, writing in the 1st century AD, used beryllus to
refer to a variety of minerals having long, prismatic
crystals with hexagonal cross-sections.
His smaragdus
included the Egyptian beryl among other green stones, but he
also recognized its relationship with beryllus: "many people
consider the nature of berulli to be similar to, if not
identical with, that of smaragdi" (Pliny's Natural History
37.16-20 in Eichholz, 1962, p. 212-227; Healy, 1999, p.
202-203, 241-245). The modern name 'emerald' is derived from
the ancient smaragdus, a word that can be traced back at
least as far as the late 4th or early 3rd century BC when it
was used by the Greek writer Theophrastus as a catchall for
green gemstones (Theophrastus' On Stones 23-27 in Caley and
Richards, 1956, p. 50-51, 97-109). The Egyptian green beryl,
however, was almost certainly unknown to him. The first
mention of beryl (smaragdos) mining in Egypt was by the
Greek geographer Strabo about 24 BC (Strabo's Geography
17.1.45 in Jones, 1959, p. 120-121). When mining began in
Wadi Sikait is not known precisely but, given the almost
total absence of green beryl in Ptolemaic jewelry, it must
have been late in the Ptolemaic period and probably not much
before Strabo wrote about it.
True emerald has a bright, uniform, medium to dark green
colour and is transparent. Beryls of this quality are very
rare not only in Wadi Sikait but throughout the surrounding
beryl-mining region. The Egyptian green beryl almost always
has a pale colour and a cloudy translucency (due to abundant
fluid inclusions), and it also commonly contains minute
mineral inclusions (usually phlogopite or actinolite, or
their weathered clay-mineral equivalents). It is ironic,
therefore, that Egypt's famous 'emerald mines' produced very
few true emeralds.
The poor quality of Egyptian green beryl has been attested
to repeatedly in both the ancient and modern literature (for
a partial summary see Sinkankas, 1981, p. 542-548). For
example, Pliny the Elder complained that the "Ethiopian
[i.e., Egyptian] smaragdus is ... rarely flawless or uniform
in tint" (Pliny's Natural History 37.18.69 in Eichholz,
1962, p. 218-219). Although Egypt's ordinary green beryl may
not have been highly esteemed by the Romans, it was still
clearly much valued by them for jewelry. It was the hardest
green gemstone available to them and it also had the added
mystic of coming from fabled Egypt.
Perhaps another appeal
of beryl was its naturally faceted hexagonal prisms that
mimicked the more costly cut gemstones. Unlike in recent
centuries, when beryl has been ground into faceted stones,
the Romans used the natural hexagonal prisms cleaved from
crystals. These were either fixed into metal settings or
drilled along the prism axis and strung as beads.
Author James A. Harell
More on emerald necklace:
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Geology of Wadi
Sikait Emeral Mine
Much has been written about the geology of the Wadi Sikait
region (e.g., MacAlister, 1900; Hume, 1934, p. 109-125;
EGSMA, 1951, p. 82-94; Basta and Zaki, 1961; El Shazly and
Hassan, 1972; Hassan and El Shatoury, 1976; EGSMA, 1992, p.
31-83; and Abdalla and Mohamed, 1999). The map in Figure 2
is based on both this literature and fieldwork by the
author. This is the first map of Wadi Sikait to combine
topographic and geologic information, and also to show the
distribution of ancient mine workings. The rock units in the
map legend are listed chronologically downward from youngest
to oldest. Not shown on the map are numerous diabase dikes
that postdate the granite and intrude all other rock units.
The schist melange also contains some small pockets of
metadiorite-metagabbro as, for example, around the Middle
Village. All the rock units date to the Late Proterozoic era
and belong to the Pan-African Series except for the granite-granodiorite
gneiss, which dates to an earlier part of the Proterozoic (Hassan
and Hashad, 1990).
The geologic occurrence of beryl in Wadi Sikait has been
well described by Basta and Zaki (1961) and Abdalla and
Mohamed (1999), and their findings are consistent with what
is known generally about the origins of beryl deposits
elsewhere (Sinkankas, 1981, p. 339-356). For green beryl tn
form, two relatively rare elements need to be present:
beryllium and chromium. Beryllium-bearing minerals are most
commonly associated with hydrothermal veins that are
offshoots of silicic magma bodies. At Wadi Sikait, such a
magma body produced dae granite with its quartz and
pegmatite veins. These veins generally vary from a few
centimetres up to one metre in thickness, and have intruded
all older rock units in the area. The veins are now much
deformed and so commonly appear as discontinuous lenticular
bands and pods. The occurrence of beryl is intimately linked
with these Be-enriched veins, especially those of milky
quartz, which are the most plentiful (Fig. 4).
Only minute amounts of Cr substituting for A1 in the beryl
crystal structure are needed to give the mineral a green
colour, with darker shades produced by higher Cr
concentrations. Although V can also colour beryl green,
chemical analyses have shown that Cr is the colorant for
Wadi Sikait beryl. Unpublished analyses of five beryl
specimens from Wadi Sikait reveal Cr concentrations ranging
from 150 to 1013 ppm, and averaging 552 ppm (EGSMA, 1992,
Table 3.4; A. El Dougdoug, Geology Dept., Cairo University,
Egypt, pers. comm.). Chromium is commonly found in rocks of
mafic composition, where it occurs as an impurity in mica
and amphibole minerals through substitution for the Al and
Fe in their crystal structures. In Wadi Sikait, these rocks
are represented by phlogopite and actinolite schists in the
schist melange. The actinolite schist occurs as thin sheets
and lenses within the much more abundant phlogopite schist.
Beryl occurs mainly in the phlogopite schist and
quartz/pegmatite veins, and is restricted to within tens of centimetres of their contact. It is found as individual
crystals and, more often, as small clusters of crystals.
Crystals can be up to 3 cm in length but most are much
shorter. The beryl in the quartz/ pegmatite veins varies
from colourless or white to light green but in the
phlogopite schist the colour ranges from light to dark
green. Given that the schist is a source of Cr, it is not
surprising that this rock would have the greener beryl,
including true emerald. The geologic occurrence of green
beryl at Wadi Sikait is very similar to that at Canada's
Regal Ridge. Here the green beryl, which is coloured by Cr,
occurs within mica schist close tn its contact with quartz
veins spawned by a nearby granite intrusion (Groat et al.,
2002, p. 1330). Contrary to what Giuliani et al. (1998, p.
513-514) claim, Wadi Sikait is not a Type II emerald
deposit, where Be-bearing hydrothermal fluids permeated Cr-
or V-bearing rocks along thrust faults or shear zones. Both
Wadi Sikait and Regal Ridge classify as Type I emerald
deposits, where Be-bearing quartz or pegmatite veins from a
granitic pluton intruded Cr- or V-bearing mafic or
ultramafic rocks.
Ancient emerald mining
settlements at Wadi Sikaitthat date to the Roman and early Byzantine
periods (Foster et al., in press; Sidebotham et al., 2004).
The largest of these is the so-called South Village, and
this is the only one where archaeological excavations have
been undertaken. The buildings here, as in the other two
settlements, are constructed from slabs of quartz-muscovite
schist . The well-preserved late Roman structure
is probably an administrative building, but
could also be a temple. The South Village is particularly
notable for its rock-cut temple, which is carved out of talc
schist. From conservation work done on this
structure, it is known that it goes back at least as early
as the 1st century AD, and poorly preserved Greek and
hieroglyphic inscriptions hint at an earlier Ptolemaic date.
Both the quartz-muscovite and talc schists are common
lithologies in the schist melange unit. The next largest
settlement is the Middle Village, which is perched midway up
the west side of the mountain known as Gebel Sikait. Here there is also a well-preserved, ancient roadway
leading down to Wadi Sikait.
Modern prospecting and small-scale
emerald mining occurred in Wadi
Sikait during the first three decades of the last century.
Most traces of this activity are found around the Middle and
North villages, where modern workings occur amongst the
ancient ones. Past attempts at reopening the Wadi Sikait
emerald
mine were all unsuccessful because of the generally poor
quality and, hence, low market value of the emerald.
Prospecting and Extraction Methods
The ancient emerald mine workings are mostly open-cut trenches of up
to a few metres in depth. These follow the quartz/ pegmatite
veins within the phlogopite schist. Many adits, shafts and
tunnels, some extending over 100 m, pursue these veins deep
underground. Where less than a few tens of centimetres
thick, the vein together with 1-2 m of schist on both sides
was removed, but for the thicker veins the schist was
generally extracted along just one side. From the tool marks
preserved in the schist, it is clear that the Roman miners
used flat-edged chisels and, to a lesser extent, pointed
picks for their excavations. None of these tools,
which were presumably cast from iron, have yet to be found
in Wadi Sikait. It is likely that the quartz and pegmatite
veins, which are too hard for such tools, were removed by
stoping with the actual digging occurring only in the much
softer phlogopite schist.
The underground portions of the Wadi Sikait emerald mine have not
yet been studied. There are instead only a few passing
comments from earlier visitors. For example, MacAlister
(1900, p.544) says "the mining is of a most primitive
character ... the ancients simply excavated ... a network of
long and very tortuous passages just large enough to allow
the body being dragged through, and only in a very few cases
was any attempt made at ... excavating the entire seam." An
unpublished report from the Egyptian Geological Survey and
Mining Authority (EGSMA, 1951, p. 86) provides additional
details: "some emerald mines are very elementary, the galleries are
very narrow and tortuous, that one has to creep all the time
... [whereas] other emerald mines are nearly perfect; [their] walls
were cleanly cut, shafts and levels were systematically dug,
tunnels are [so] wide and high that it is easy to walk
comfortably through ... [and] steps were carved in the floor
of some inclined tunnels... [and] in all cases, one can
notice the presence of big pillars of country rock being
left for roof support.
Conclusions
The ancient emerald miners knew that emeralds was to be found along the
contact between the quartz/pegmatite veins and phlogopite
schist, and so probably rested every such association where
visible on the surface (Fig. 4). The fact that not all the
vein-schist contacts in Wadi Sikait have been mined is an
indication that either the beryl deposits are erratic in
their occurrence or they were never fully exploited.
Although beryl occurs in the quartz/pegmatite veins, it
could not have been extracted from these hard rocks without
great effort and large losses of crystals through breakage.
Given this as well as the generally inferior color of beryl
in the veins, the ancient miners were probably interested
only in the more easily worked phlogopite schist. The beryl
crystals were presumably cut out of this rock with a
sharp-pointed metal tool, perhaps an iron blade or burin.
From the great piles of fine-grained tailings around many of
the workings, it appears that the removal of beryl crystals
from the schist was done at the mine site.
In Egypt's Wadi Sikait, ancient miners extracted emerald and
other green beryl from the contact zone between phlogopite
schist and intrusive quartz and pegmatite veins. This is
essentially the same geologic occurrence as the beryl on
Canada's Regal Ridge. The world's oldest emerald mine (Wadi
Sikait) and youngest emerald discovery (Regal Ridge) are
separated by two millennia, yet are linked by not only their
similar geology but also their common purpose--to satisfy
people's desire for emerald jewelry. It is through the
practice of archaeological geology that such links are made.
Acknowledgements
The author wishes to thank Steven E. Sidebotham, Professor
of Roman Archaeology at the University of Delaware (USA) and
Director of the Wadi Sikait Project, for permission to
publish the present paper. This ongoing project, for which
the author is the site geologist, has been supported by
grants from the National Geographic Society. Thanks are also
due to A. P. Sabina and especially J.D. Greenough for their
comments on an earlier draft of this paper.
Resume
L'emeraude qui est une variete de beryl vert transparent,
etait l'une des pierres precieuses les plus prisees dans
l'Antiquite La plus vieille mine d'emeraude connue est
situee dans la vallee de montagne de Wadi Sikait dans le
desert oriental de l'Egypte, ou l'extraction a probablement
debutee vers la fin de la periode ptolemaique durant le
premier siecle A.C. Cependant, le gros des travaux
d'extraction date des periodes romaines et byzantines, de la
fin du premier siecle avant J.C. jusqu'au sixieme siecle
apres J.C. Les Romains utilisaient le mot smaragdus pour
designer l'emeraude et designait la region de Sikait par
l'expression Mons Smaragdus ou la montagne d'emeraude. Une
etude de geologie archeologique de Wadi Sikait a ete
entreprise dans le but de cartographier les anciens sites
d'extraction, d'en deduire
les anciennes methodes
d'extraction utilisees et de circonscrire la distribution
des gisements d'emeraude. On a decouvert que les gisements
d'emeraude et autres beryls verts sont localises dans la
zone de contact separant une zone de schistes a phlogopite
et de veines intrusives de quartz, d'une zone de pegmatites.
Les excavations pratiquees dans la formation plus tendre du
schiste a phlogopite a l'aide de ciseaux a pointe aplatie et
de pics pointus, sont peu profondes pour la plupart, et
forment des tranchees a ciel ouvert qui longent les zones de
veines de quartz et de pegmatites. Certaines d'entre-elles
qui se prolongent en soussol jusqu'a 100 m de profondeur
sont peu explorees. Il est interessant de noter que le cadre
geologique du beryl de Wadi Sikait, la plus vieille mine
d'emeraude au monde, est essentiellement le meme que celui
du plus recent gisement decouvert a Regal Ridge dans les
Territoires du Yukon au Canada.
References
Aston, B.G., Harrell, J.A. and Shaw, I., 2000, Stones, in
Nicholson, P. T. and Shaw, I. (eds.), Ancient Egyptian
Materials and Technology: University of Cambridge Press,
Cambridge, UK, p. 5-77.
Abdalla, H.M. and Mohamed, F.H., 1999, Mineralogical and
geochemical investigation of emerald and beryl
mineralization, Pan-African Belt of Egypt--genetic and
exploration aspects: Journal of African Earth Sciences, v.
28, n. 3, p. 581-598.
Basta, E.Z. and Zaki, M., 1961, Geology and mineralisation
of Wadi Sikeit area, South-Eastern Desert: Journal of
Geology of the United Arab Republic (later Egyptian Journal
of Geology), v. 5, n. 1, p. 1-36.
Caley, E.R. and Richards, J.F.C., 1956, Theophrastus On
Stones: Ohio State University Press, Columbus, Ohio, 238 p.
EGSMA, 1951, Report on the Prospecting Expedition in Wadi El
Gemal Area, 1950-1951 (unpublished internal report):
Egyptian Geological Survey and Mining Authority, Cairo,
Egypt, 95 p.
New technique discerns
emeralds' beginnings - Gemstone Geography
Once an emerald leaves its country of origin and circulates
around the world, the gem's provenance becomes murky.
Scientists have now developed a nondestructive method for
determining the source of an emerald, even down to the mine
from which it was extracted. That information can affect the
gem's price and make it easier for historians to reconstruct
ancient trade routes.
An emerald-tracking procedure that measures the ratio of two
oxygen isotopes in a microscopic sample from a gem has been
available for a few years (SN: 3/11/00, p. 175).
Unfortunately, that method is not foolproof, says Philippe
de Donato of the Ecole Nationale Superieure de Geologie in
Vandoeuvre-les-Nancy, France. Emeralds from Russia,
Pakistan, and Madagascar often have the same ratio of oxygen
isotopes, making them indistinguishable from one another.
A new analysis technique focuses on water trapped in an
emerald's minute channels, de Donato and his colleagues
reported last week at the Materials Research Society meeting
in Boston. These channels, distributed throughout the stone,
are just wide enough to fit one or two water molecules. The
researchers homed in on a naturally occurring form of water
in which an atom of deuterium, a doubly heavy isotope of
hydrogen, replaces an atom of the more common hydrogen.
Emeralds (Colombia and Pakistan) photo by pustule In the new technique, de Donato's team shines infrared light
on an emerald. Oxygen-deuterium bonds in the gem's water
molecules absorb specific wavelengths of the light, yielding
an absorption spectrum that serves as an optical signature.
The investigators used this signature to link various
emeralds with their known sites of origin. "Because this
method is completely nondestructive, we can make all the
measurements we want," de Donato says.
Not only could the researchers distinguish between an
emerald from Russia and one from Madagascar, they could
pinpoint the specific mine in each country from which the
emerald came. So far, the scientists have distinguished
among emeralds from 10 mines in seven countries. They have
also discriminated between natural emeralds and synthetic
ones.
Why water molecules in emeralds from different parts of the
world produce different optical signatures is unclear.
De Donato says it may have to do with the presence of soil
nutrients, such as sodium and potassium, whose
concentrations vary from region to region and that seep into
an emerald's crystal structure. The proximity of these
elements to water in the gem's channels could influence the
spectrum, he says.
"This could straighten out a lot of the confusion
surrounding where ancient emeralds come from," says Fred
Ward, a gemologist and book author in Bethesda, Md. For
instance, when Spanish explorers brought emeralds from
Colombia to the Middle East in the 16th century, they kept
the origins of their gems a secret to protect their sources,
Ward says.
The method could also be useful for documenting new
emeralds, he says. For example, if gem dealers can confirm
that a stone is from Muzo, Colombia, the most famous emerald
mine, they can sell it at a premium.
Author A. Goho COPYRIGHT Science Service, Inc. & Gale Group
region. Although it has been suggested that
the emerald deposit at Habachtal near Salzburg, Austria was
worked as early as the Roman period, there is no conclusive
evidence that it was known prior to the Middle Ages (Sinkankas,
1981, p. 371-77). However, Giuliani et al. (1998, 2000) have
shown that the green beryls from Egypt and Austria are
distinguishable by their oxygen-isotopic composition, and
such testing, if applied to Roman jewelry, may yet reveal
Habachtal's true historical significance.
AD) and Early
Byzantine (5th through early 6th centuries AD) periods. All
the other mining sites are strictly Roman-Byzantine or
Islamic (mid-6th century AD onward) in date. Beryl mining
ceased in Egypt with Spain's discovery of superior-quality
Colombian emeralds in the 16th century AD. It is commonly
reported in the literature (e.g., Giuliani et al., 2000, p.
631) that emeralds were used in Egypt as early as the 18th
dynasty (16th through 14th centuries BC) of the New Kingdom.
This claim, however, is based on the misidentification by
archaeologists of amazonite (a green variety of microcline)
as emerald (Lucas and Harris, 1962, p. 389-390). The
earliest unequivocal evidence for emerald mining in Egypt
dates to Ptolemaic times, and even for this period the
evidence is scant. It was the Romans who were primarily
responsible for developing the mines, and it was they who
gave the mining district its ancient name, Mons Smaragdus or
'Emerald Mountain'.
and a cloudy translucency (due to abundant
fluid inclusions), and it also commonly contains minute
mineral inclusions (usually phlogopite or actinolite, or
their weathered clay-mineral equivalents). It is ironic,
therefore, that Egypt's famous 'emerald mines' produced very
few true emeralds.
such a
magma body produced dae granite with its quartz and
pegmatite veins. These veins generally vary from a few
centimetres up to one metre in thickness, and have intruded
all older rock units in the area. The veins are now much
deformed and so commonly appear as discontinuous lenticular
bands and pods. The occurrence of beryl is intimately linked
with these Be-enriched veins, especially those of milky
quartz, which are the most plentiful (Fig. 4).
Modern prospecting and small-scale
emerald mining occurred in Wadi
Sikait during the first three decades of the last century.
Most traces of this activity are found around the Middle and
North villages, where modern workings occur amongst the
ancient ones. Past attempts at reopening the Wadi Sikait
emerald
mine were all unsuccessful because of the generally poor
quality and, hence, low market value of the emerald.
phlogopite a l'aide de ciseaux a pointe aplatie et
de pics pointus, sont peu profondes pour la plupart, et
forment des tranchees a ciel ouvert qui longent les zones de
veines de quartz et de pegmatites. Certaines d'entre-elles
qui se prolongent en soussol jusqu'a 100 m de profondeur
sont peu explorees. Il est interessant de noter que le cadre
geologique du beryl de Wadi Sikait, la plus vieille mine
d'emeraude au monde, est essentiellement le meme que celui
du plus recent gisement decouvert a Regal Ridge dans les
Territoires du Yukon au Canada.%20photo%20by%20pustule.jpg)
In the new technique, de Donato's team shines infrared light
on an emerald. Oxygen-deuterium bonds in the gem's water
molecules absorb specific wavelengths of the light, yielding
an absorption spectrum that serves as an optical signature.
The investigators used this signature to link various
emeralds with their known sites of origin. "Because this
method is completely nondestructive, we can make all the
measurements we want," de Donato says.