Crystal Roses of the Namib Desert


"A rose by any other name will smell as sweet"
The Namib’s roses display crystalline beauty but lack in fragrance as they bloom on the desert’s floor.

Germination of desert roses is slow by any standards. Measured in geological time, these frail formations require the right mix of elements to start growing. Their soil is the barren desert substratum...the water they receive is magnitudes less than the evaporation that sucks moisture from their arid environment….their fertilizer comes in the form of gypsum, a lifeless mineral…and they require hundreds of years to bloom in all their rose–like splendour. Another attribute is that they are classified as a member of the salt family. The geological description of a desert rose evokes images of physics and chemistry: “A radially symmetric group of crystals with a fancied resemblance to a rose, formed in sand, soft sandstone, or clay. The crystals are usually of calcite (calcium sulphate), less commonly of barite or celestite”.

 

The French description is more evocative. “Croǔte de nappe” means “a small piece, which has been forced away from its roots”. This aptly describes the growth process of lifeless crystals from a bed of gypsum or, as the common name has it, “Plaster of Paris”. These sub–surface crusts appear on all the continents, including Antarctica. They contain a mix of mainly sand grains, which are weathered quartz crystals, thereby also earning for them the alternative name of sand roses. Their requirement for growth is that precipitation, whether rain or fog, must always be less than evaporation. If this is exceeded, the surplus moisture dissolves the gypsum accumulations and no crystals form. The desert roses will subsequently wilt and die back to a shapeless jumble of chemicals.

Various theories exist about the formation of these much sought–after crystals in the Namib Desert. Until recently, the most widely accepted one was based on the work of Dr. Henno Martin. The German–born geologist became famous more for his popular writing than for his discipline. His classic book “The Sheltering Desert” (translated from the original “Wenn es Krieg gibt, gehen wir in die Wüste”) graphically describes the ordeal he and a colleague experienced when they sought refuge in the Namib to avoid internment during World War II. Dr. Martin’s theory is fascinating. Namib gypsum is presumed to form when frequent fogs, laden with sulphur, drift far into the desert. This sulphur originates from the seabed of the Benguela Current when its organic richness decomposes without the presence of oxygen. Upwelling over an area of 15 000 km2 in the Benguela lifts the hydrogen sulphide, which smells much like rotten eggs, to the surface. Fog and foul–smelling gas combine to produce sulphur dioxide and sulphur trioxide. The fog subsequently precipitates on the desert’s surface, transforming the resident calcium carbonate–rich soils and rocks into calcium sulphate, or gypsum. In this chemical exchange, water and carbon dioxide gas are released as by–products. Moreover, reasoned Dr. Martin, because fog penetrates furthest inland at low altitudes, the gypsum–rich soils lying below 500 metres elevation are the ideal locations for desert rose growth. Furthermore, salt pans located within 50 km of the coast are probably the most ideal habitat for “germination” of these unlikely roses.

Like many scientific theories, this long–accepted one of Henno Martin was open to scrutiny by a recent researcher. Dr. Frank Ekhardt from Germany studied at Oxford University for his dissertation, making the following observation: “It seems that Martin’s model is a lot less effective than people have thought” He continues: “Instead, there seems to be enough evidence suggesting that gypsum in the Namib forms as a result of much more established processes that can be found in deserts throughout the world. These processes seem to be concealed by the hyper–aridity and the age of the Namib”. Consequently, it appears that more research is necessary to determine the exact origin of Namib Desert roses.

Whatever science unravels about Namibia’s desert roses, certain facts are indisputable. It is established that gypsum crusts extend to a depth of about one metre. Mature rose crystals can grow to as much as 50 cm in diameter, described geologically as a “subsurface  macrocrystalline, lenticular  matrix”. This interprets to mean a large pattern of interlocked crystals that resemble a double convex lens. These delicately formed patterns are totally dependent on the interaction of many factors, some of them as yet unknown to science. Several million tones of gypsum deposits with 90% purity are estimated to exist within a radius of 50 km from Swakopmund and Walvis Bay. Lower grade deposits in the central Namib are calculated to be in the order of several million tones.

Fortunately for the natural environment, geologists regard desert roses as minor mineral occurrences and no proper assessment of their economic potential has been made. Their value to science may be to demonstrate changes in the distant past of water, climate and soil regimes. Nevertheless, the signs of uncontrolled exploitation are there. Unscrupulous collectors take these artefacts of nature without possessing the permit necessary to remove them. They are then either sold for profit or, in the case of casual collectors, left to lie forgotten in some remote part of the world, far from their pristine environment. Would it not be preferable to allow these delicate crystal flowers to bloom undisturbed in the desert and have them admired in their natural habitat by visitors?

 

Text by Dr. Hu Berry

Originally published by Venture Publications in ‘Flamingo’ September 2004

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