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Bruce Cairncross: Department of Geology, Rand Afrikaans University, P.O. Box 524,
Auckland Park, 2006, South Africa.
Karl Messner: P.O. Box 3036, Symridge, 1420, Gauteng, South Africa. and
Eric Farquharson: 355 York Avenue, Ferndale, Randburg, 2194, South Africa
Introduction
For several years, outstanding crystals of aegirine from "Zomba", Malawi, have been offered
for sale. The aegirine has been associated with aesthetic smoky quartz, microcline, zircon and
other rare species such as parisite, epididymite, fergusonite and eudyalite. The exact locality of
the pegmatites has however never been clearly described or recorded and most, if not all,
specimens have merely been labeled "Zomba, Malawi". In the most recent excursion in
October 1997, the local Malawians agreed to show the precise locality where the crystals were
being collected. This article therefore records and summarizes this expedition and also shows
some of the outstanding specimens that have been obtained during the latest expedition.
History and Geology
The area of mineralogical interest falls into a part of the Chilwa Alkaline Province which, as its
name suggest, consists predominantly of Cretaceous alkaline intrusives and extrusives
associated with the East African rift 1. The Chilwa province consists of
several granite, syenite and nepheline-syenite plutons that are associated with extrusive
carbonatites and agglomerates. From the collector's standpoint, two important types of
pegmatites are present in the area. In the Chinduzi-Chikala range of mountains, nepheline-syenite pegmatites occur.
The October 1997 Expedition
In October 1997 a group of Johannesburg mineral collectors, Karl Messner, Paul Botha and
Eric Farquharson, decided to undertake a collecting trip to the Mount Malosa plateau in
Malawi. Up until about two years ago, driving along this stretch of road was very different
because of the civil war, and one had to be escorted by an armed army convoy. Continuing
onwards for another 250 km, the border between Malawi and Mozambique was reached
where the border crossing was again rather straightforward. After entering into Malawi and
passing through the capital city, Blantyre, it was only another 60 km to the Zomba plateau.
Mount Malosa
The local Malawians are miners in the truest sense, because the Malawi government has
granted them mining certificates to prospect for minerals and several of them also have legal
claims to the sites where the minerals are excavated. Most of the minerals that were obtained
on the expedition were purchased at this market, over a thousand specimens of aegirine,
quartz, feldspar, zircon and a few of the rarities. Specimens ranged in size from thumbnail,
single crystals, to museum-sized matrix specimens of aegirine, quartz and feldspar that
weighed over 15 kg. It was also during this trading session that the plans were discussed to
visit the exact sites from which the specimens were being collected. The specimens that were
to be self-collected during the following few days were to be of secondary importance and
quality to those that were purchased. Even so, the minerals that were self-collected were very
important because the actual location where the specimens are coming from could be
examined first hand. The miners told the group that they were the first Europeans to ever set
foot on some of these very remote and dangerous localities. The next morning the group left
with three guides to hike into the Malosa mountains. The journey began heading north, with a
steep descent down Zomba Mountain into a deep valley and then hiking up the opposite side
of the valley again onto the Malosa plateau. The path is narrow so while barefoot Malawians
can put one foot in front of the other, feet wearing heavy hiking boots do not fit so well in the
"groove" and walking becomes an awkward, unnatural exercise of deliberately putting one
foot in front of the other, in a parallel line.
The exact site where the crystals are excavated is breathtakingly dangerous. One wrong step
can prove fatal, and it was soon realised that without professional climbing equipment the cliff
faces could not be properly explored. Yet, the three Malawian guides who were barefoot had
no problem clambering up and down the treacherous slopes, an activity that would certainly
resulted in death had anyone else tried to do this.The guides explained that better and larger
specimens come from further down the 600 800 metre cliff faces.
Conclusion
Access to the area from where the collectable minerals are found is not easy. One has to take
all provisions, camping and digging equipment along because no facilities or shops exist on the
mountains. In order to spend a few days collecting, one has to camp on the summit of the
mountain it is not possible to hike in and out every day. The mineral specimens are all
collected from outcropping pegmatite veins. To say that the conditions of collecting crystals
are hazardous would be to make a huge understatement. Most of the more easily accessible
pegmatites have been excavated and their crystals long since removed and sold. The remaining
pegmatites are those that outcrop on the very steep scarp faces of the northwestern part of
Malosa mountain. Local Malawians scale these treacherous slopes barefoot, hanging
precipitously above drops of several hundred metres to the valley below. Finally, the logistics
of undertaking the trip are very frustrating and tedious and much time can be wasted trying to
undertake fairly rudimentary and basic tasks.
Description of Recent Mineral Discoveries
2
The list provides a list of the main minerals that are reported from the region. Those marked
with an asterisc (*) are discussed below because these species were obtained during the most
recent visit. Detailed descriptions of the other minerals can be found in Peterson and
Grossman (1994). An important unreported discovery that was made was the presence of
galena. This particular specimen has small needle-like crystals of aegirine attached, confirming
that is comes from this locality.
Aegirine
Large numbers of very aesthetic aegirine crystals continue to be collected. These vary considerably in their crystal form, size and association with other mineral species. Extremely lustrous onyx-black single crystals up to 22 cm occur. Groups of elongate, prismatic aegirine crystals form haystack-like groups. Some aegirine crystals are studded with white microcline crystals. Others are intergrown with prismatic, doubly terminated beige zircons. Some quartz crystals have inclusions of very acicular, hair-like microscopic crystals of aegirine that impart black phantoms to the otherwise clear quartz.
Arfvedsonite
Euhedral, sharp prismatic crystals of arfvedsonite were one of the most interesting minerals
obtained. These are black and display typical aligned striations on the prism crystal faces,
parallel to the c-axis. Stubby crystals 4 5 cm long are common but the largest measured over
10 cm although these were weathered and corroded. Associated species include microcline,
zircon, aegirine and quartz.
Epididymite
A few small (millimetre-sized) epididymite crystals were observed on some of the specimens (X-ray diffraction analysis confirmed this identification). However, one of the largest epididymite crystals yet reported from this locality was obtained during the most recent trip. This is a terminated hexagonal crystal 4.5 cm long and 4 cm in diameter, on a matrix of aegirine and smoky quartz. The crystal is colourless and displays a highly micaceous texture. Other specimens of epididymite are more typically elongate, thin prismatic crystals, very commonly included within quartz crystals.
Fergusonite-(Y)
Only a few fergusonite-(Y) crystals were obtained. These display the typical tapering habit and
are pale yellow.
Goethite
Goethite is prevalent on most of the specimens that come from the area. It forms a brown rust-coloured coating to most specimens. One interesting specimen that is also reported here for the first time is a goethite pseudomorph after what is believed to be parisite . The crystal that is being replaced is flat, tabular and hexagonal in outline, but is now composed entirely of iron hydroxides.
Another new discovery was attractive, sharp cubic crystals of pyrite, up to 1 cm on edge, now altered to goethite. These occur as groups of crystals some nucleated onto aegirine crystals.
Galena
Galena has never been reported from the Zomba region. One specimen that was in amongst the many hundreds of aegirine was a small galena specimen. At first it was thought that the galena was collected at some other locality in Malawi and merely added into the Zomba material. But on cleaning the specimen and examining it, the presence of small, attached aegirine crystals confirmed its source as indeed originating from Zomba.
Parisite-(Ce)
Parisite-(Ce) has been reported from the Zomba massif. One of the largest crystals to date is a terminated, 3.2 cm hexagonal crystal (2.1 cm diameter) associated with aegirine and a second, smaller naturally etched parisite. The parisite displays a common feature of having a tapering profile towards the flat, pinacoidal termination. As with other smaller crystals that were found on other specimens, this large specimen is has typical corroded faces.
Potassium feldspar
All the feldspar found at Mount Malosa is potassium feldspar. Although no definitive analyses were carried out, a few random eldspars were examined and proved to be microcline. The largest euhedral crystal measures 25 cm on edge. Groups of microcline are common and often associated with quartz, smoky quartz, aegirine and arfvedsonite. The feldspar is white to very pale-cream in colour and twinning is very common. Some K-feldspar crystals have pitted or corroded crystal faces.
Quartz
An abundance of quartz is common within any batch of Zomba material. The crystal sizes range from thumbnail to over 25 cm. The quartz is most commonly clear and colourless. However, inclusions of acicular aegirine produce almost black crystals. Smoky quartz is also common. The habits of some of the quartz specimens are somewhat unusual. Most are the common hexagonal shape but some crystals are extremely flattened. Many quartz crystals have overgrown aegirine. A few quartz specimens have included yellow to dull orange impurities that are as yet unidentified. Quartz is associated most commonly with aegirine and potassium feldspar, as well as zircon.
Siderite
A few specimens of rhombohedral, tan-coloured siderite crystals form the matrix to quartz and feldspar.
Zircon
Zircon crystals up to 4 cm have been collected. Some are opaque, light brown tetragonal crystals, but other specimens have gemmy, transparent orange crystals. The abundance of zircon, occurring as loose crystals as well as composite aggregates, and as zircon associated with most of the other minerals found at Zomba, attest to it being relatively common.
1: Eby, G.N., Roden-Tice, M., Krueger, H.L., Ewing, W., Faxon, E.H. and Woollley, A.R. 1995. Geochronology and cooling history of the northern part of the Chulwa Alkaline Province, Malawi. Journal of African Earth Sciences, 20, 275-288.
2: Bloomfield, K.. 1965. The geology of the Zomba area. Geological Survey of Malawi Bulletin No. 16, 193 pages and Petersen, O.V. and Grossmann, M. 1994. Some pegmatite minerals from Zomba district, Malawi. Mineralogical Record, 25, 29-38.
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