Desert Sand Roses
By Barry Taylor
There is a mysterious and fantastic crystal formation that grows inside shifting sands as if by magic and as you may expect it is usually found in arid regions. When discovered no two crystal growths are exactly alike; each group consists of interlocking flattish blades as separate creations. These crystals do often have a flower like appearance and when discovered were thought to be petrified blooms.
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Saudi Arabian Gypsum Roses
Crystal rosettes form in the Miocene coarse sand deposits of Saudi Arabia, in the Rub-Al- Khakli area of the Eastern Province, especially the Coastal Region that runs from Half Moon Bay and Al-Uqayr. Some clusters from this location can be up to 1m across, they often have a reddish brown hue; these rosettes appear as clusters of blades and discs, interlocking and merging together based on crystallographic lines, also they have a Poikilotopic texture, which means that large crystals enclosed smaller ones of another mineral.
Environment of formation
All the Desert Roses are formed by the evaporation of water drawn up from shallow aquifers in which the brine becomes saturated, being fed by nearby saline waters. These particular deposits are rare; most exposures will form clumps and veins of the fibrous gypsum called Satin Spa. The gypsum is usually found together with other evaporates such as Halite, and Anhydrite in which massive deposits are the norm. Often they occur in rhythmic bands or layers that are typical of the southern Mediterranean basin hence Morocco, Algeria, Tangiers, Tunisia and Egypt are well known locations, all these are where the desert meets the Mediterranean coast.
Rich mineral waters
Concentration of the necessary Calcium Sulphate in the waters need to be at least three times the level of normal seawater and this occurs as a result of an increased concentration of Brine in the aquifers that are fed underground from the nearby Arabian Gulf. The desert roses themselves consist of 65% Gypsum and 10% Quartz Sand, this sand gives the crystals their colour, ranging from pale off white to rusty red, brown and even black. The remaining 25% of the flowers is often made up of other evaporates such as Halite (Salt), Anhydrite and Dolomite.
How the flowers are found Often the flower like clusters are uncovered by windblown sand movement following storms, clusters form at less than 50mm below the surface down to the Water Table which is at least 1m below surface. The typical environment is in areas of mainly dry basins, these are called Sabkhas in Saudi Arabia. Other similar deposits to these are found all around the Mediterranean wherever deserts are close by and similar can be found in the Paracas Desert, Peru, which is the same type of coastal location for the necessary evaporate planes found near to the coast. Other locations such as Morocco produce a large number of these desert flowers; this is due in part to the established connections with mineral and fossil dealers that are already providing a ready market. Also in Mexico are the areas of Las Choias and Chihuahua close to desert areas and having the same established infrastructure, new to the list is Namibia.
Apart from the above locations there are low temperature gypsum rich sand concentrations where sand flowers are found such as the sand pits near Canterbury. Gypsum crystals are also found in exposures of waterlogged fossil clays with a high sulphide concentration producing single and fishtail twins of gypsum crystals e.g. Hastings Beds of the Weald.