Chemistry: Be3Al2SiO36 Beryllium Aluminum Silicate

1
BERYL
Chemistry Be3Al2(SiO3)6 Beryllium Aluminum
Silicate Class Silicates Subclass
Cyclosilicates Uses Gemstone, mineral
specimens and source of beryllium Varieties
Aquamarine (blue) Emerald
(green) Goshenite (colourless)
Green beryl Heliodor (yellow)
Morganite (pink) Red beryl
2
Beryl belongs to the hexagonal class of minerals.
The most common crystal shape of beryl requires
at least two crystal forms to form a complete
crystal. The first is a hexagonal prism. The
second is the basal pinacoid. The combination of
these two forms gives the prismatic and tabular
shapes with which we are so familiar.
3
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.
4
850 carat uncut emerald, Columbia
Heliodore
Aquamarine and green beryls
Morganite, USA
5
Iron is the impurity which is responsible for
both the blue color of aquamarines and the yellow
of heliodor. The blue color is attributed to an
Fe2 ion located in a channel site, while the
yellow color is attributed to an Fe3 ion located
in an octahedral Al site. The infinite shades of
green between these two extremes are a result of
mixing these two ions in various amounts.
6
Red Beryl is the rarest form of beryl, which
includes emeralds and aquamarines. The only
crystals suitable for faceting are found in the
Wah Wah Mountains (the Violet Claims), near
Beaver, Utah. Currently, this is the only place
in the world where gem quality Red Beryl is
found.
Goshenite
7
The deep red color for which red beryl is known,
is also attributed to Mn2, although little work
has been done to confirm this.
8

• References
• Dietmar Schwarz, 2542? ?????????????????????????
  ?????????????? ????
• ?????????????????????. ????????????????
  ????????????????????
• Delaney,J.V.Patrick, 1996. Gemstones of
  Brazil-geology and
• occurrences.REM-Revista Escola de Minas,
  Brazil
• Keller, P.C., 1990. Gemstone and their origins.
  Geoscience Press Inc.,
• Mexico
• Sauer,J.R, 1992. 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

9
EMERALD DEPOSITS
This 632 carats specimen is considered to be one
of the world's greatest emeralds. Moreover, while
most uncut emeralds have six sides, the Patricia
Emerald is dihexagonal, or twelve-sided. The
emerald was found in the Colombian Andes in 1920,
in the Chivor Mine. It is named for the
mine-owner's daughter.
10
CLASSIFICATION OF EMERALD DEPOSITS

• 1. Granitic Pegmatite-Hydrothermal Type
• I/A In mafic-ultramafic rocks
• Australia, Brazil, Madagascar,Nigeria,
  Parkistan, Russia, USA, Zambia, Zimbabwe
• I/B In (meta-) sedimentary rocks
• Australia, Norway
• 2. Tectonic-Hydrothermal Type
• II/A Thrust, fault and shear-zones in
  mafic-ultramafic rocks
• II/A1 In volcano-sedimentary series
  Austria, Brazil
• II/A2 In oceanic suture zones
  Afgahanistan, Egypt, Parkistan
• II/B Thrust, fault-zones in sedimentary rocks
• Colombia

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Pegmatite Model

• Simple Pegmatites
• Complex Pegmatites
• - metasomatic
• - recrystallized
• - desilicated

12
Hydrothermal Model
Sources of water - magmatic - metamorphic -
connate - meteoric etc. Sources of heat -
magma - geothermal gradient Sources of ore metals
13
Hydrothermal Model 1
14
Hydrothermal Model 2
15
Emerald Deposits of Colombia

• 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.

16
Geology of the Emerald Deposits

• Colombian Andes
• Eastern Cordillera limestones, shales,
  (igneous and metamorphic rocks)
• Central Cordillera Granitic rocks
• Western Cordillera Granitic rocks
• Villeta Formation
• Lower Cretaceous, carbonaceous and calcareous
  shales, thick, intensely folded and fractured
  hosts emerald-bearing veins (calcite, pyrite,
  albite etc.)
• Muzo Deposits emerald-bearing pyrite ( albite)
  veins
• Chivor Deposits emerald-bearing calcite veins

17
Origin of the Emeralds

• Classification Tectonic hydrothermal of type
  IIB
• Ages of Mineralization
• Muzo 32 - 38 Ma
• Chivor 65 Ma
• Sources of Elements
• Hydrothermal solution H2O, CO2, (CnHn), Na,
  K, Cl, Ca, Mg, Fe, Li, Mo,
• (Be,
  Sn..), SO4
• Parent rocks Si, Al, Mg, K, Ca, Fe, Cr, V,
  Be, REE
• EMERALD Be3Al2Si6O18(Cr, V, Fe, Mg)

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• Muzo - Emerald in calcite veins that 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
  calcite and yellow-brown needles of the mineral
  parisite.
• Mines owned by government since 1871 have been
  leased to various operators since then. Five year
  leases instituted in 1977 discontinued in 1982(?)
  due in part to poor recovery brought about by
  rapid mining techniques (dynamite and
  bulldozers). 10 year leases were most recently
  held by two companies, Tecminas and Coesminas,
  who developed underground workings.
• Once the most prolific emerald mines in the
  world.

www.gemtec.com
19

• Chivor - Emerald in quartz-albite-apatite veins
  that invade a gray calcareous shale.
• Chivor emerald has a lower S.G. and lower R.I.
  (S.G.2.69, R.I.E1.571 R.I.O1.577) than Muzo
  emerald. Crystals tend to be more elongate than
  those from Muzo.
• Color is said to tend toward a bluer green
  ("cool green") as opposed to the slightly
  yellower green ("warm green") of Muzo.
  Characteristic inclusions are pyrite and albite.
• The Chivor mines are privately owned owners pay
  a 25 royalty on all production to the Colombian
  government. Recent reports indicate little
  production, but the possibility of new ownership
  renewed hope that these mines would once again
  become productive.

20
Emerald with dolomite and calcite Muzo,
Colombia. Despite being damaged, the emerald is
approx. 4 cm in size and has a deep green colour.
It is embedded in a mixture of calcite and
dolomite crystals in addition to being joined
with a rare calcium-cerium-fluoride-carbonate
parasite. The piece has a hole through it and was
thus most probably used as a pendant.
http//www.nhm-wien.ac.at/
21
Emeralds are also being mined at Cosquez (near
Muzo) and Gachala (near Chivor)
El Perfecto, a fine emerald specimen from
Coscuez.
An uncut 850 carats Gachala emerald.
22
http//www.palagems.com/emerald_colombia.htm
23
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.
24
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.
25
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.
26
Cenicero
calcite
Cambiado
27
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.
28
(No Transcript)
29
Albite Rock
Cenicero
Cambiado
Albite Rock
30
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.
31
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.
32
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.
33
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 probable that the Cenicero
was first deposited, following close on to the
faulting movement, 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.
34
MINING PRODUCTION
35
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.
36
A view of the Coscuez Mine.
37
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.
38
Material being traded locally
Mining the stream bead are done by children,women
and men. They work the tailings of the mine.
39
CHIVOR EMERALDS
Muzo emerald
Trapiche emrald
Pre-Colombian artifact
40
Emerald crystal on white calcite and pyrite from
the El Indio corte in Muzo which produces some of
the best emerald faceting rough. The white
calcite and pyrite nodule are a great indicator
of Muzo origin.
41
INCLUSIONS
Emeralds are usually clouded by many inclusions.
The nature of the inclusions is usually
indicative of the source of the emerald. Emeralds
from Colombia normally have three phase
inclusions. These consist of a solid (usually a
pyrite crystal), a liquid (salt water?) and a gas
(usually CO2). Emeralds from India usually have
"square," dark inclusions (biotite) whereas those
from South Africa have dark needle-like
inclusions and those from the Ural Mountains in
Russia have actinolite needles that resemble
bamboo poles.
www.gemtec.com
42
THREE PHASE INCLUSION This is one of the most
diagnostic inclusions found in Colombian
Emeralds.
CALCITESharply defined,well-formed calcite
crystal is a unique feature of Colombian stones.
ALBITEWell-formed albite crystal
PYRITEAnother typical inclusion seen in
Colombian Emeralds.
43
SPIRALBanner of fluid drop inclusions winding in
a spiral formation around a growth tube.
PARISITE CRYSTAL Found only in Colombian
Emeralds from the Muzo mine. The mineral is
composed of or rare earth elements. It is
extremely dense and radioactive.
QUARTZQuartz with double terminations in
polarized light
ZONINGParallel zone of differing pigmentation
(chromium concentration))
44
FINGER PRINT This is a Natural "Finger Print"
inclusion formed by minute, liquid-filled cavities
TUBE This tube-like-two phase inclusion common
in Chivor stones
GROWTH 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 appears to be
calcite precipitations.
45
987 Carat Emerald
The 'Angel of the Andes' is considered to be a
very fine and unusual emerald specimen due to its
multiple terminations at 90 degrees to the main
crystal. It is currently in the collection of Tim
Schmanski of the Red Beryl Mine. It was found in
December of 1992 at the Chivor mine in Colombia.
Apparently, two brothers found the stone and one
of them decided to take it to America. Needless
to say he sold it, and the other brother has
vowed his revenge.
http//www.rockhounds.com/rockshop/angel1.html
46
NINE EMERALDS, represented here as white boxes,
hark from a variety of different mines (dark
green bands), based on their ratio of 18O to 16O
(y-axis). A Gallo-Roman earring's gem (1) comes
from Pakistan. The St. Louis stone in the crown
of France (2) is from Habachtal in Austria.
Hauy's emeralds (3) are from Austria and Egypt.
Gems from the Nuestra Se?ora de Atocha come from
Colombian mines (top four sources), as do three
Nizam stones (5). Another is from Afghanistan..
47
TOPKAPI DAGGER, from Topkapi Palace in Turkey, is
studded with emeralds that, like the stones in
other Old World treasures, may have originated in
the New World.
48
This 217.8 ct Mogul emerald is a fine example of
the early Colombian stones that were treasured by
the Mogul nobility in India. The Islamic prayer
in this dramatic representation includes the date
1695 AD. The Mogul emerald is the property of
Allan Caplan, New York. It has recently been sold
at auction for 2.2 million. (http//www.gia.edu/g
andg/shownews.cfm?id77)