Chemistry: Be3

Al2

(SiO3

)6

Beryllium Aluminum Silicate

Class: SilicatesSubclass: CyclosilicatesUses: Gemstone, mineral

specimens and source of beryllium

Varieties : Aquamarine (blue) Emerald (green) Goshenite (colourless) Green beryl Heliodor (yellow) Morganite (pink) Red beryl

BERYL

Beryl belongs to the hexagonal class of minerals. The most common crystal shape of

beryl requires at least two crystal forms to fo rm a complete crystal. The first is a hexagon

al prism. The second is the basal pinacoid. T he combination of these two forms gives the

prismatic and tabular shapes with which we are so familiar.

When the impurity is chromium, the result is the rich green for which emeralds are prized. Emeralds have a decidedly blue tinge to them, unlike green aquamarine which is characterized by a yellowish hue. Studies have also shown that the presence of vanadium in addition to chromium can enhance the green color.

850 carat uncut emerald, Columbia

Aquamarine and green beryls

Heliodore

Morganite, USA

Iron is the impurity which is responsible f or bot h t he bl ue col or of aquamarines and t he yel l owof heliodor. The blue color is attrib uted to an Fe+2 ion located in a channel si

te, while the yellow color is attributed to a n Fe+3 ion located in an octahedral Al site

. Thei nfi ni t e shades of gr een bet ween t he set wo ext r emes ar e a r esul t of mi xi ng t h eset wo i ons i n var i ous amount s.

Red Beryl is the rarest for m of beryl, which

includes emeralds and a quamarines. The only cry

stals suitable for faceting are found in the Wah Wa

h Mountains (the Violet C laims), near Beaver, Utah

. Currently, this is the onl y place in the world wher e gem quality Red Beryl i s found.

Goshenite

The deep red col or for which red

beryl is known, is also attributed to Mn+2, althou gh little work ha

s been done to c onfirm this.

References

• Dietmar Schwarz, 2 5 4 2 ใ เอกสารประกอบการ “ อบรมเชิ�งปฏิ�บ�ติ�การเร��อง มรกติ

“และพลอยติระก�ลคอร�นดั�ม . ภาควิ�ชิาธรณี!วิ�ทยา มหาวิ�ทยาล�ยเชิ!ยงใหม$• 1996Delaney,J.V.Patrick, . Gemstones of

- Brazil geology and - occurrences.REM Revista Escola de Minas, Brazil• Keller, P.C., 1 9 9 0 . Gemstone and theiroooooooo o ooooooooo ooooo ooooo Mexico• 1992Sauer,J.R, . Emeralds around the

world. Rio de Janeiro• Moroz, I.I., and Eliezri, I.Z., 1999. Mineral inclusions in emeralds from different sources. The Journal of Gemmology, Vol. 26, No.

-2, p357 363• http://www.geo.utexas.edu/courses/347k/redesign/gem_notes/Beryl/ • http://www.gemtec.com

This 6 3 2 carats sp ecimenisconsideredt o be one of t he world'sgreatestemeralds. Mor eover , whi l e mo stuncut emer al ds have sixsi des, t he PatriciaEmerald is dihexago

- nal, or twelve sided. T he emerald was found

in the Colombian And es in 1 9 2 0 , in the

Chivor Mine. It is nam -edf or t he mi ne owner ' sdaught er .

EMERALD DEPOSITS

CLASSIFICATION OF EMERALD DEPOSITS

1 - . Granitic Pegmatite Hydrothermal Type - . Granitic Pegmatite Hydrothermal TypeI/A - In mafic ultramafic rocks• Australia, Brazil, Madagascar,Nigeria, Parkistan, Russia, USA, Zambia, ZimbabweI/B - In (meta ) sedimentary rocks• Australia, Norway

- 2. Tectonic Hydrothermal Type - 2. Tectonic Hydrothermal Typeoooo - - Thrust, fault and shear zones in mafic ultramafic rocks• 1II/A - In volcano sedimentary series : Austria, Brazil• 2II/A In oceanic suture zones : Afgahanistan, Egypt, ParkistanII/B - Thrust, fault zones in sedimentary rocks• Colombia

Pegmatite Model

• Simple Pegmatites

• Complex Pegmatites - metasomatic - recrystallized - desilicated

Hydrothermal Model

Sources of water- magmatic- metamorphic- connate- meteoric etc.

Sources of heat- magma- geothermal gradient

Sources of ore metals

Hydrothermal Model 1

Hydrothermal Model 2

• about 60% of world production

• worlds finest emeralds.

• 2 mining districts northeast and east of Bogota, Muzo and Chivor.

• ancient mines originally worked by Aztecs; "rediscovered" by Spanish in 1537 (Chivor) and 1559 (Muzo).

• long history of intermittent production continuing to present-day.

Emerald Deposits of Colombia

Geology of the Emerald Deposits

Colombian Andes• Eastern Cordillera : limestones, shales,

(igneous and metamorphic rocks)• CentralCor di l l er a : Granitic rocks• WesternCor di l l er a : Granitic rocks

Villeta Formation Lower Cretaceous, carbonaceous and

calcareous shales, thick, intensely folde d and f r act ur ed -host s emer al d bear i n g vei ns (calcite, pyrite, albite etc.)

Muzo Deposits : - emerald bearing pyrite (+ albite) vei ns

Chivor Deposits : - emer al d bear i ng cal ci t e vei ns

Origin of the Emeralds

Classification : Tectonic hydrothermal of type IIB

Ages of Mineralization• - Muzo : 3 2 3 8 Ma• Chivor : 6 5 Ma

Sources of Elements• Hydrothermal solution : H

2 O, CO

2 , (CnHn ),

Na, K, Cl, Ca, Mg, Fe, Li, Mo, (Be, Sn..), SO

4

• Parent rocks : Si, Al , Mg, K, Ca, Fe, Cr, V, Be , REE

• EMERALD : Be3

Al2

Si6

O18

(Cr, V, Fe, Mg)

- Muzo Emerald in calcite veins that - Muzo Emerald in calcite veins that invade black shale. invade black shale.

• Rough is often color zoned with paler core.

• Both Muzo and Chivor emeralds are characterized by - three phase inclusions

- trapped fluid containing gas, fluid, and crystals of halite.

• Muzo emeralds often contain inclusions of cal ci t e - and yellow brown

needles of the mineral parisite .

• Mines owned by government since 1871; have been leased to various oper

ators since then. Five year leases instit uted in 1977 discontinued in 1982(?) du

e in part to poor recovery brought abou t by rapid mining techniques (dynamite

and bulldozers). 10 year leases were m ost recently held by two companies, Te

cminas and Coesminas, who developed underground workings.

• o ooo ooo o ooo oooooooo oo ooooo o oooo in the world.

www.gemtec.com

- Chivor - Chivor oo ooooo - - in quartz albite apatite veins - - in quartz albite apatite veins

that invade a gray calcareous that invade a gray calcareousshale.shale.

• Chivor emerald has a lower S.G. and lower R.I. (S.G.=2 .6 9 , R.I.

E =1 .5 7 1 ; .. O 1577= . ) t han Muzo emerald. Crystals tend

to be more elongate than those fr om Muzo.

• Color is said to tend toward a bluer green

("cool green") as opposed to the sl i ght l y yellower green

("warm green") of Muzo. Charact eristic inclusions are pyrite and

albite .

• The Chivor mines are privately owned; owners pay a 2 5 % roya

lty on all production to the Colom bian government. Recent reports

indicate little production, but the possibility of new ownership

renewed hope that these mines would once again become produc

tive.

Emerald with dolomi te and calcite – Muzo,

Colombia. Despite be ing damaged, the em

erald is approx. 4 c m in size and has a d

eep green colour. It is embedded in a mixtu

re of calcite and dolo mite crystals in additi

on to being joined wit -h a rare calcium ceriu- - m fluoride carbonate

parasite. The piece h as a hole through it a nd was thus most pro

bably used as a pend.

-http://www.nhm wien.ac.at/

Emeralds are also being mined at Emeralds are also being mined at Cosquez (near Muzo) and Gachala (near Chivor) (near Muzo) and Gachala (near Chivor)

El Perfecto, a fine emerald specimen from Coscuez.

An uncut 850 carats Gachala emerald.

http://www.palagems.com/emerald_colombia.htm

General Geology

The geology of the Eastern Cordillera of the Colombian Andes is known only in the most general way. The principal geological formations exposed in the emerald-bearing region are shown in the following columnar statement:

Quaternary

Tertiary

Cretaceous

1. Red sandstone with septarian nodules.

2. Compact sandstone; gray fossiliferous limestone between two

layers of gray shale with plant impressions.

3. Black, carbonaceous shale and shaley limestone. Carries Muzo

emerald deposits and Cipaquira salt deposits.

4. Siliceous schists and conglomerates, with jasper, flint, etc.

These rocks are compressed into great north-south folds and igneous phenomena are largely lacking.

Geology of the Emerald Deposits

The emeralds are found almost entirely in calcite veins that traverse a black, carbonaceous, rather intensely folded formation consisting of thin-bedded shale and limestone. This Emerald Formation lies discordantly upon steeply dipping strata, barren of emeralds, composed of heavier beds of carbonaceous limestone intercalated with black shale, and called the Cambiado. Between the emerald formation and the Cambiado and ever in close proximity to the plane of discordance are three rock types of great significance in furnishing direct evidence of the origin of the emeralds. These are

(1) albite rock,

(2) a light-gray rock composed of a soft granular aggregate of calcite, dolomite, quartz, pyrite, and other minerals, called by the miners Cenicero.

(3) aggregates of large, well-formed calcite rhombs in a fine-grained matrix, forming rock masses known locally as Cama.

In addition, a few pegmatite veins have recently been discovered in the Cambiado.

The Emerald Formation.

The emerald formation, Figs. 5, 6, 7, consists of thin beds (averaging 2 cm. in thickness) of shale and limestone alternating, the shale in predominance. The shale is a dense, black rock, soiling the hands with excess carbonaceous matter, and most of it effervesces with acid from the presence of calcium\carbonate. The limestone is likewise black with carbon but differs from the shale in carrying calcium carbonate in excess of silicate material. The shale-limestone beds are gently to severely folded, in places contorted (Figs. 5 and 7). The folds are small, irregular in strike and pitch, non-persistent, and lie in all directions; in short, they indicate no general direction of compression. Their disposition suggests local rather than regional pressure. Fractures are prominent, for the most part healed by calcite and consequently marked by veins and seams of white. Well-defined joints are inconspicuous; faults are present, but, with the exception of the plane of overthrust separating the emerald formation and the Cambiado, are for the most part not easily traced.

calcite

Cambiado

Cenicero

The emerald is seldom found in the shale or limestone alone. Its usual home is the calcite veins. In many places the beds carry nodules of pyrite or seams of that mineral in well-crystallized condition; and some phases are shot through with well-formed pyrite crystals.

AlbiteRock

CambiadoCenicero

AlbiteRock

Age

The ages of the Emerald Formation and Cambiado are fixed as Cretaceous by the fossils, chiefly ammonites, that have been found rather abundantly in them. Miguel Gutiérrez places the Cambiado as Lower Cretaceous and the Emerald Formation as Middle Cretaceous. The present writer presents no fossil evidence but feels that further paleontological study is needed before a correlation closer than “lower Cretaceous” can be accepted for the rocks of the emerald deposits.

Origin

The evidence bearing on the origin of the emerald has been presented in descriptive form. It may be summarized under four heads, as follows:

1. The association of such minerals as emerald, parisite, fluorite, apatite, albite, and barite in a sedimentary formation implies the introduction of material from an external source.

2. The presence of pegmatites is significant, because the conditions under which pegmatites form are fairly definitely understood. The mineral content of the pegmatites is thought to correlate their formation with the general period of mineralization.

3. The presence of albite rock (highly albitized limestone) and its spatial relation to a zone occupied by the Cenicero and Cama indicate the passage of strongly effective mineralizing solutions. The albite rock itself is thought to represent a contact metamorphic rock, not of the normal type (because of the absence of such characteristic minerals as garnet, epidote, pyroxene, amphibole, etc.) but of the type characterized by V.M. Goldschmid as that due to “pneumatolitic contact metamorphism,” a type that develops later in the cooling of, and more distant from, the parent magma than the normal type.

4. Structural conditions indicate that the emerald formation was overthrust to its present position upon the Cambiado, and that this movement was followed by a period of mineralization which attained its most conspicuous results along the fault plane and its economic results above (and not below) that plane. That the emerald veins are the result of the same period of mineralization that produced the Cenicero, Cama, and albite rock, is thought to be clearly indicated by the mineral content and spatial connection that may be traced between the four. The barren calcite veins in the Cambiado are probably of the same period of mineralization also; for they are post-faulting (Figs. 8a and 8b) and in places are connected with the Cama. These considerations together present practically conclusive evidence that the emerald is one effect of a period of mineralization growing out of the intrusion of a body of igneous rock. That exposures of this rock have not been thus far discovered should have little weight as evidence. We may infer further that the emerald was deposited under gas-aqueous (pneumatolitic) conditions, although the general temperature of mineralization throughout was probably below 575°.

Other inferences may be drawn and suggestions made. It is possible that the overthrusting and folding of the emerald formation is due to the crowding effect of the igneous intrusion; this makes an attractive and reasonable hypothesis. Then, the fact that the veins of the Emerald Formation carry emeralds, while those of the Cambiado are barren, or, in short, that the emeralds all lie above the plane of overthrust, although non-economic mineralization proceeded below, suggests that the solutions, entering along

the shattered fault plane, effected a separation there, their liquid portion permeating the rocks on either side, their gaseous portions rising and therefore recording passage (by emerald deposition) only in the rocks above. The presence of the two unusual types of deposits, the Cenicero and Cama, raises a difficult question; but it seems proba

ble that the Cenicero was first deposited, following close on to the faulting movemen

t, and then the Cama was introduced and, accompanying it (farther out from the fault plane), the calcite veins were developed. Again the carbon content of the emerald formation interposes itself as a common factor, suggesting the possibility that it may have been essential to the formation of the emerald in some way, either by its precipitative action, or by its reducing action on chromium, the coloring agent of emerald. Finally, the question arises as to the source of the calcite so prominent in the seams and the veins throughout, and it appears probable that the calcium carbonate displaced from the Cambiado upon its albitization is sufficient to form these bodies, without magmatic contribution of that material.

MINING & PRODUCTION

A view of an open pit mining operation. The terraces at the bottom are bulldozed. This method of mining is disappearing due to its high cost.

A view of the Coscuez Mine.

Typical open pit,bulldozers clearing the surface in search of an emerald vein.

A "trusted" person overseen the works. Attention must be at peak levels to locate and identify the gem bearing veins.

Material being traded locally

Mining the stream bead are done by children,women and men. They work the tailings of the mine.

CHIVOR EMERALDS

Muzo emerald Trapiche emrald Pre-Colombian artifact

Emerald crystal on white calcite and pyrite from the El Indio corte in Muzo whi

ch produces some of the best emerald fa ceting rough. The white calcite and pyrit

e nodule are a great indicator of Muzo origin.

INCLUSIONS

Emeralds are usually clouded by many inclusions. The nature of the

inclusions is usually indicative of th e source of the emerald. Emeralds

from Colombia normally have thre e phase inclusions . These consist o

f a solid (usually a pyrite crystal), a liquid (salt water?) and a gas (usua

lly CO2

). Emeralds from India usua lly have " square," dark inclusions (

biotite) whereas those from South Africa have dark - needle like inclusi

ons and those from the Ural Mount ains in Russia have actinolite needl

es that resemble bamboo poles.

www.gemtec.coo

THREE PHASE INCLUSION

This is one of the most diagnostic inclusions found in Colombian Emeralds.

PYRITEAnother typical inclusion seen in Colombian Emeralds.

ALBITEo ooo-oooo oo oooooo ooooooo

CALCITESharply defined,well-formed calcite crystal is a unique feature of Colombian stones.

SPIRALBanner of fluid drop inclusions winding in a spiral formation around a growth tube.

QUARTZQuartz with double termination’s in polarized light

ZONINGParallel zone of differing pigmentation (chromium concentration))

PARISITE CRYSTAL ooooo oooo oo ooooo oooo oo oooooo

from the Muzo mine. The mineral is composed of or rare earth element

s. It is extremely dense and radioactive.

FINGER PRINT This is a Natural "Finger Print" inclusion formed by minute, liquid-filled cavitiesTUBE

- - This tube like two phase inclusion common in Chivor

stonesGROWTH STRUCTURE Notice the "Strain" and the typical growth pattern in this natural Colombian Emerald

DROP OF OIL EFFECT A velvety appearance can be

noticed in this Muzo Emerald ap pears to be calcite precipitations.

987 Carat Emerald

The 'Angel of the Andeso oo oooooooooo oo oo o

very fine and unusual e merald specimen due t

o its multiple terminatio ns at 90 degrees to the

main crystal. It is curren tly in the collection of Ti

m Schmanski of the Re d Beryl Mine. It was fou

1992nd in December of at the Chivor mine in Co

lombia. Apparently, two brothers found the ston

e and one of them decid ed to take it to America.

o ooooooo oo ooo oo oooo it, and the other brother

has vowed his revenge.

http://www.rockhounds.com/rockshop/angel1.html

NINE EMERALDS, represented here

as white boxes, hark from a variety

of different mines ( dark green bands),

ooooo oo ooooo ooooo of 18 O to 16 -O (y a

- xis). A Gallo Roman 1earring's gem ( )

comes from Pakista n. The St. Louis sto ne in the crown of F

rance (2 ) is from Habachtal in Austri

a. Hauy's emeralds 3( ) are from Austria and Egypt. Gems fr

om the Nuestra Se๑ ora de Atocha com

e from Colombian mines (top four sou rces), as do three N

5izam stones ( ). A nother is from Afgh

anistan. .

TOPKAPI DAGGE

R, from Topka pi Palace in

Turkey, is stu dded with em

eralds that, lik e the stones i n other Old W

orld treasures , may have ori

ginated in the New World.

This 217.8 ct Mo gul emerald is a fine example of

the early Colomb ian stones that w ere treasured by the Mogul nobilit

y in India. The Isl amic prayer in th

is dramatic repre sentation includ

es the date 1695 AD. The Mogul e

merald is the pro perty of Allan Ca plan, New York. I

t has recently be en sold at auctio

n for $2.2 million.

(http://www.gia.edu/gandg/shownews.cfm?id=77)