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Gemstones
 Amethyst
AMETHYST,
the purple variety of quartz
Specimens
Amethyst is the purple
variety of quartz and is a popular gemstone. If it were not for
its widespread availability, amethyst would be very expensive. Its color is unparalleled,
and even other, more expensive purple gemstones are often compared to its
color and beauty. Although it must always be purple to be amethyst, it can
and does have a wide range of purple shades.
Amethyst is prevalent in most places of
Zambia but major production is in the Mapatizya area in the
Mwakambiko hills and in the Mumbwa-Namwala area.
Amethyst deposits in the Mwakambiko
Hills occur in a northeast trending belt. They intrude basement
rocks. The amethyst belt is some 30 km long 15 km wide and appears
to be related to the boundary faults separating Karoo from Basement.
The deposits have been known since the 1950s and Northern Minerals
started commercial production in 1956, which is now being run as
Kariba Minerals Ltd.
Annual production of amethyst is about
700 tonnes. Currently the major producer is Kariba Minerals Limited,
which is jointly owned by the Government and Lonrho, a private
company.
In general the potential is substantial
and high quality materials are becoming more and more apparent.
 Aquamarine
Specimens
Aquamarine is the blue, or perhaps more correctly, blue-green or aqua
variety of the mineral beryl. Other gemstone color varieties that belong
to beryl include emerald, morganite, and heliodor. Other colors of beryl
are simply referred to by their color, such as red beryl.
Aquamarine
is colored by trace amounts of iron that find their way into the crystal
structure. Most gem aquamarines have been heat treated to produce the
popular blue-green colors from less desirable yellow or pale stones.
Aquamarine bearing pegmatites are found
in the Lundazi, Mkushi and Itezhi Tezhi areas and intruded the
Basement rocks during post-Katangan, pre-Karoo times.
Beryl
Beryl is often unknown to the general public, even the gemstone-buying
public. However, it is one of the most important gem minerals. Beryl is
colorless in pure form; it is the many different impurities that give
beryl its varied coloration. Without these splendid color varieties, beryl
would be a rather ordinary gemstone with only average fire and brilliance.
Emerald is the green variety and Aquamarine is the blue variety of beryl.
Other colors
of beryl are also used as gemstones but are not as well known.
The greenish-yellow
variety is called Heliodor.
The pink variety is called Morganite.
The colorless variety is called Goshenite.
The name beryl is used for the red and golden varieties, which are simply
called red beryl and golden beryl, respectively.
Emerald is highly prized and is one of the most valued gemstones. Its
green color is peerless and all other green gemstones are compared to
its intensity. Emerald specimens are often "flawed" with mineral
inclusions and fractures; unlike other gems, these are considered part
of the stones' "character." These flaws actually help determine
natural from synthetically-produced stones. Uncut emerald specimens are
rare on the mineral markets, probably because even low grade emeralds
can carry a high price when cut as gems. Especially hard to find are true
"in-matrix" specimens. Fakes are often produced with natural
crystals glued into a "host" rock and then sold as an in-matrix
specimen with a highly inflated price.
 Emeralds
Emerald is the green variety of the mineral beryl. Other gemstone color
varieties that belong to beryl include aquamarine, morganite, and heliodor.
Other colors of beryl are simply referred to by their color, such as red
beryl.
The wonderful
green color of emerald is unparalleled in the gem kingdom. Emerald's precious
green color is caused by small amounts of chromium and enhanced by traces
of iron. Unlike other beryls, emeralds often contain inclusions and other
flaws. These flaws are not looked on as negative aspects for emerald like
they would be for other gemstones. Indeed, these flaws are considered
part of the character of the stone and are used to assure the purchaser
of a natural stone.
Emeralds are found in the Miku-Kafubu
Area. They were emplaced in the pre-Katangan time in the Muva
sediments
 Tourmaline
Most
people consider tourmaline to be a single mineral. But in
fact it is
a group named for several different, but closely related minerals. Members
of the Tourmaline Group are favorites among
mineral collectors. Their rich and varied colors can captivate the eye.
Even the black opaque
tourmalines can shine nicely and produce sharp crystal forms. Tourmalines
are cut as precious gems, carved into figurines, cut as cabochons, sliced
into cross-sections and natural specimens are enthusiastically added to
many a rock hound's collection.
There are many unique properties of tourmalines. First, they are piezoelectric
which means that when a crystal is heated or compressed (or vibrated)
a different electrical charge will form at opposite ends of the crystal
(an electrical potential). Conversely if an electrical potential is applied
to the crystal, it will vibrate. Secondly they are pleochroic which means
that the crystal will look darker in color when viewed down the long axis
of the crystal than when viewed from the side. This property goes beyond
the idea that the crystal is just thicker in that direction. Even equally
dimensioned crystals will demonstrate this trait. This property can be
used as an advantage by gem cutters who may wish to enhance a crystal's
pale color or weaken a strongly colored crystal.
The four
most common and well known tourmalines are distinguished by their color
and transparencies. Elbaite is the gemstone tourmaline and comes in many
varied and beautiful colors. It is transparent to translucent and is highly
prized as minerals specimens and as gemstones. Elbaite is easily the most
colorful of all the gemstones.
The iron
rich schorl is the most abundant tourmaline and is black and opaque. It
is a common accessory mineral in igneous and metamorphic rocks and can
form nice crystals. Although too opaque to be used as a gemstone, schorl
is used as an ornamental stone when found as inclusions in quartz, a stone
is called "tourmalinated quartz". Usually when someone refers
to tourmaline they are referring to either elbaite or schorl.
The two other
more common tourmalines; dravite and uvite are much less common than elbaite
or schorl, but they are getting noticed for their beautiful specimens.
Some of dravite's crystals are nicely formed, translucent brown and they
can reach a rather large size. Uvite is a green translucent to opaque
tourmaline that is growing in popularity and is being cut as a gemstone.
The Tourmaline
Group has a general formula of AX3Y6(BO3)3 Si6O18(O, OH, F)4. The A can
be either calcium or sodium. The X can be either aluminum, iron, lithium
or magnesium. The Y is usually aluminum, but can also be chromium or iron.
Some potassium can be in the A position, some manganese can be in the
X position and some vanadium can be found in the Y position, but these
elements are usually not represented in the formulas of the tourmaline
members.
 GARNETS
Garnets are a ubiquitous component of
metamorphic rocks throughout Zambia. Gem garnets found in Zambia
include: red garnets (generally mixtures of pyrope and almandine),
rhodolite( a pale violet type of pyrope) and spessartite ( an orange
to red-brown variety). The most productive garnet deposits are a
group of mines centred around Sangu and Doost mines northwest of
Lundazi.
OTHER GEMSTONES
Other gemstones that have been found in
Zambia include topaz, opal and agates, citrine. Agates occur in
vesicles in the Karoo basalts found in Livingstone and elsewhere in
Zambia.
The diamond
potential of Zambia is an area that requires serious attention in
future. De Beers carried out extensive work over a period of 30
years and they managed to identify over 100 kimberlite pipes. De
Beers reported many occurrences of small diamonds and indicator
minerals but no economic or commercial deposits were found. The
kimberlite and lamproite pipes found in Zambia can be divided into
the following domains; Tanzania-Mweru, Luangwa, Mid-Zambezi,
Mulobezi-Kafue and Kabompo. The failure by De Beers to find an
economic deposit in Zambia while some of the world's most prolific
and richest deposits are being, or have been mined, in the adjoining
countries of Botswana, Angola, Democratic Republic of Congo and
Tanzania, begs explanation. It is apparent that more research and
exploration is required in this particular area.
CONTACT
ADDRESSES
Permanent Secretary
-
Ministry of Mines and Minerals Development
P. O. Box 31969, LUSAKA,
Tel. 254107
Fax. 251224
Email:
mines@zamnet.zm
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