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Gypsum Rosettes

Introduction

Ever wonder how sandstones are created....do you even know what they are? These beautiful formations occur naturally through geological phenomenon. The beautiful sandstone creation is also known as the gypsum rosette. Gypsum rosettes can have many appearances, they can be light colored with great luster, dark colored with a foggy luster, and it can even be composed of sand!

Actually gypsum rosette is not a rose but rather a mineral which crystalizes in a unique rosette growth pattern. Gypsum Rosettes can be found all across the world. They form lightning fast in terms of geoligical time. They are created in tens to hundreds of years. A unique legend, orignating from the Middle East, claims that for every one of these stones that are found, Allah will bless the person who found it with good luck.

Products of the Geologic Process

A gypsum rosette is not a rose at all, it is a mineral which crystalizes in a unique rosette growth pattern. Their are many varieties, some look remarkably like a rose flower with its pedals open, while others from into beautiful bladed spheres. Gypsum is an evaporite, which means its crystals form during the evaporation of water. The crystals are shaped like prisms or flat plates, and can grow up to 1 meter. Gypsum can appear as transparent crystals (selenite); fibrous, elongated crystals (satin spar); granular and compact masses (alabaster); and in rosette-shaped aggregates called desert roses. Some even form large clusters comprised of many small rosette crystals which are the color of sand and usually brown. In order for gypsum rosettes to form they must have an arid environment, a large source of CaSO4 (calcium sulfate), and a seasonal fluctuation of water. In terms of geological time gypsum rosettes form very rapidly in that they form in tens to hundreds of years. This would explain their abundance across the world.

In Suadi Arabia, sand roses are found in the flat brine-rich Sabkhas (desert areas) which are prevailant in the Eastern Providence. Water from the Gulf of Arabia, which is full of brine, seeps underground into the Sabkhas. The brine rich water chemically concentrates the CaSO4 which then crystallizes into the mineral gypsum (CaSO4, 2H2O) As the water evaporates and deposits throughout the seasons, the gypsum crstals grow in the intergrain pore spaces trapping the surrounding loose sand. Thus the supberb geological phenomenon creates these beautiful gypsum rosettes! The image below is a picture of a selenite desert rose (left) and a baryte desert rose (right). The Baryte desert rose contains a higher degree of sand than the selenite desert rose on the left. The image on the right is an odd shaped salenite crystal formation. These Crystals grow as opaque sand-filled crystal clusters with mica-like sheets. These clusters can be HUGE (room-sized) or just single ball rosettes!

The United States also has a vast amount of rosettes. They differ greatly from the appearance of the sand roses in the Middle East. Gypsum rosettes commonly occur in the clay layer of the earth's crust. In the same geological phenomenon gypsum foms in the clay as a result of rising and evaporating moisture while creating certain chemical concentrations. The water from rivers and streams floods sometimes which chemically concentrates the CaSO4 which is abundant in the soil. The calcium sulfate then crystallizes into the mineral gypsum (CaSO4, 2H2O) As the water evaporates and deposits throughout the seasons, the gypsum crstals grow in the intergrain pore spaces trapping the surrounding loose sediment surrounding it. This phenomenon creates gypsum rosettes like the ones pictured below. These rosettes are usually found among areas of floods and are distributed throughout the banks of the floodway. Within these floodway deposits one can see the horizontal banding of the rosette forms. This banding may reflect changes in the permeability of the clays as well as the effect of depth and unfavorable growth conditions nearer to the surface.

There are two typical forms of rosettes found. In more shallow regions is an amber colored compact ball of intergrown crystals with small, thin blades pointing out from the core seems to be the standard.. Sometimes large transparent amber blades protrude out of this core producing spectacular specimens.

In deeper layers, the crystals in the rosette are larger, more distinct and blocky. The color in these specimens are typically yellow, but can also be colorless. Large blades protruding from these rosettes are also blocky. In both forms, some of the large blades may have clay or a rock included. All the crystals are fluorescent and phosphorescent, glowing a pale white under ultraviolet light.

Impacts

Most gypsum is used in the building and agricultural industries. As a building material, it's used in plaster, wallboard, cement, and ceramic tiles. In agriculture, it's used as an amendment to neutralize alkaline soil. Some gypsum that is dense and fine-grained, is called alabaster and can be carved.

Common around the world, gypsum is found primarily in sedimentary rock. In North America, crystals can be found in New York, Utah, and Oklahoma. In this region, gypsum is mined and processed in a major production plant, located in the aptly named Plaster City between Ocotillo and El Centro. The whole area is white with dust.

Literature Cited

Kjartanson, B., Baracos A., and Shields, D.H., 1983. Geological engineering report for urban development of Winnipeg Department of Geological Engineering, University of Manitoba. 77 p.

Deer, W.A., Howie, R.A., and Zussman, J., , 1992. An introduction to the common rock-forming minerals (2nd edition). Longman Scientific and Technical, England. p. 612-616.

Render F.W., , 1970. Geohydrology of the metropolitan Winnipeg area at related to groundwater supply and construction. Canadian Geotechnical Journal, vol 7., p. 243-274.

J. Young, N. Chow, I. Ferguson, V. Maris, D. McDonald, D. Benson, N. Halden (University of Manitoba)
Dept. of Geological Sciences, 125 Dysart Road, Winnipeg, MB R3T 2N2, Gaywood Matile (Manitoba Industry, Trade and Mines) Gypsum Rosettes in Southern Manitoba: Tools for Environmental Analysis and Public Awareness. Canadian Geotechnical Journal, vol 8., p. 442-474

Boerner, D.E., Bailey, R.C., Craven, J.A., Ferguson, I.J., McNeice, G.W., Jones, F.W., Wright, J.A., 1998. Electrcial conductivity and Precambrian tectonics, Geol. Soc. America, Toronto, October 1998.

Maris, V., Ferguson, I., Wu, X., Street, P., Lodha, G., 1998. TEM detection of the fresh to saline-water interface in the canadian precambrian shield, 14th International Workshop on EM Induction in the Earth, Sinaia, Romania, August, 1998.

Maris, V.G. & Ferguson, I.J., 2000. Geophysical imaging of palaeokarst features and a kaolinite deposit at Sylvan, Manitoba, Canada, SAGEEP, Arlington, February 2000.

Chow, N., Young, J., Ferguson, I.J., Maris, V., McDonald, D., Benson, D., Halden, N., Matile, G., and students of Glenlawn Collegiate 1999. Gypsum rosettes in southern Manitoba: a multidisciplinary approach. Manitoba Minerals and Mining Convention, Winnipeg, November, 1999.

Render F.W., , 1970. Geohydrology of the metropolitan Winnipeg area at related to groundwater supply and construction. Canadian Geotechnical Journal, vol 6., p. 123-158.

Baracos A., and Shields, D.H., 1985. Geological engineering and the effect of urban development of Winnipeg Department of Geological Engineering, University of Manitoba. 169p.

Deer, W.A., Howie, R.A., and Zussman, J., , 1992. An introduction to the common rock-forming minerals (2nd edition). Longman Scientific and Technical, England. p. 612-616.

Copyright ©-2001 Earlham College. Revised 12 March 2002. Send corrections or comments to greshjo@earlham.edu

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