Gemstones

Stones_AmethystAmethyst

Amethyst is simply 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 have a wide range of purple shades.

Amethyst is prevalent in most places in 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.

  Stones_Aquamarine1Aquamarine

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.

Stones_Emerald2Emerald

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.

Stones_BlueTourmalin2Tourmaline

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.

Stones_MultiTourmalineThe 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.

Stones_MandarinGarnetGarnet

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

topazOther 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.

 

 

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