New Africa Update 07 May 2021

7 May 2021

THIS week we are focusing on African minerals and enjoying their wonderful aesthetics and vibrant colours. Africa is a very ancient continent built from five Precambrian cratons of between 2 and 3.6 billion years old and bound by younger rocks of 2 billion to 300 million years. Complex metamorphic processes have altered most of these with time, resulting in a great diversity of ore deposits.

The age of minerals is a question rarely asked, whereas for fossils it is the very first. Every fossil label shows its geological age, but have you ever seen a mineral label giving such detail? The Tsumeb orebody is determined at between 580 to 550 million years old, with the paragenesis of secondary minerals following on. The Kalahari Manganese Field is hosted by well-preserved sedimentary rocks dating 2.2 billion years old, only just under half the entire age of the Earth. In today’s selection we have some great pieces from both these locations but can begin our review with one specimen which beats these in age hands down!

The Gibeon meteorite is older than the Earth, dating to the very early Solar System during the period of planetary accretion. Iron meteorites such as Gibeon are the remnant metallic cores of planetesimals, objects large enough to coalesce and differentiate into rocky shells with dense metallic cores under their own gravity but did not become one of the eight planets. This specimen weights over 0.5 kg and displays an outer crust of rusty brown iron-oxide which has been cut and polished on one surface to reveal its solid metal interior. It is classified as a Group IV A, iron, fine octahedrite and is between about 4.5 and 4.6 billion years old. That’s even older than me!

From Tsumeb we have several real beauties in terms of aesthetics and rarities. These include a Smithsonite forming dumbbell-shaped double terminated wheatsheaf crystals over a crystallised Quartz surface tinged pale sage green and orange. There is a lovely miniature Dioptase on rhombohedral crystals of Calcite and tremendous, well crystallised Beudantite. Beudantite, a lead-iron arsenate sulphate, is rare throughout the Tsumeb orebody and often crystalises as tiny pinhead crystals. This specimen is richly adorned with rosettes of glassy tabular Beudantite crystals to a few millimetres across over a carmine red, earthy iron-rich coating on Quartz. The Beudantite is clove brown tinted green and individual crystals are semi-transparent with a crackled reflective interior. Today’s Tsumeb chief rarity is a very fine miniature Schneiderhöhnite on and in a matrix of mixed Tennantite and Quartz. This very rare iron arsenate forms a fan-shaped aggregate of crystals to 1.9 cm laid flat and embedded across the dark gunmetal grey metallic matrix.

Another classic African mine is that at Berg Aukas, also in Namibia and world famous for its magnificent Descloizite. From here we have two specimens: first a stunning cabinet Descloizite composed of stacked steeple-shaped crystals, some of up to 2 cm tall, with gently rounded tapering terminations. The prism faces are complexly developed with geometrical growth patterns and crystals stack on top of one another forming small towers, so punctuating its mesmerising topography. To compliment this, a truly beautiful Smithsonite with a highly lustrous silky crystalline botryoidal surface. The Smithsonite has a slightly yellow tint to its overall barley sugar to light grey appearance and covers a matrix of red to grey-black banded Goethite.

Morocco is represented by a gorgeous fan of Azurite crystals from Touissit; a magnificent peppermint green Fluorite punctuated with Pyrite, Calcite and Quartz crystals from El Hammam; a red hot pink Cobaltoan Calcite from Aghbar mine and an arresting Vanadinite on Baryte with hexagonal burnt barley sugar orange-red crystals up to 1.3 cm from Mibladen. Finally, a showstopping Wulfenite of large tangerine-orange to buttery toffee caramel square tabular crystals, also from Touissit.

There are many fabulous specimens from one-off locations and a nice suite from the Kalahari Manganese Field in South Africa. From here take a closer look at the terrific Inesite with Calcite from Wessels mine and from the N'Chwaning mines, two Rhodochrosites and a museum quality Hausmannite.

Our whistle-stop tour of the great African continent demonstrates beauty comes before age in the mineral world, yet although we often neglect to discuss the age of minerals, these can often predate fossils by a massive margin and in the case of meteorites, by around one billion years. You have but a mere weekend to look through and enjoy this Friday’s 21 specimens, yet this is more than sufficient to pick out those must haves for your own collection. Have a great weekend.

Here is what you have to look forward to in next week's update:

Tuesday 11th & Friday 14th May - British

                                         

If you'd like to see a video of any of the specimens listed above then please contact us at orders@crystalclassics.co.uk and we'll be happy to assist you. We endeavour to respond to all enquires within 24 hours during weekdays, however at the weekend it might take us a little longer to respond.

 

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Author: JH
Categories: Updates

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