WHITE SANDS, NEW MEXICO

White Sands is in southern New Mexico, 16 mi west of the town of Alamogordo. White Sands, which covers 275 square miles, was established as a National Monument in 1933. It recently became a National Park. The elevation of the park is 4,235 feet.

White Sands is geologically situated between the San Andres Mountains to the west and the Sacramento Mountains, just east of Alamogordo, to the east. [Google Earth photo, 2018].

Aerial view, looking northwest. White Sands is in the distance, below a cloud layer on the horizon and "between" the two 
pointed-metal objects on the airplane wing.

White Sands consists of white gypsum sand dunes, the largest of their kind on Earth. 

During the Late Permian Period, about 250 million years ago, shallow seas covered the area. Evaporating seas left behind deposits of white gypsum crystals, consisting of hydrous calcium sulfate. Gypsum is very soft: 2 on the Moh's Hardness Scale. Fingernails can scratch gypsum. See my previous post on "Some Varieties of Gypsum" (Sept. 30, 2017).

Subsequent tectonism uplifted the San Andreas and Sacramento Mountains, and, over time, rain dissolved the gypsum deposits, and rivers transported the dissolved material to the nearby Tularosa Basin, which had no outlet the sea. The trapped water evaporated and gypsum was deposited (once again). Over time, weathering and erosion broke down the gypsum crystals into sand-size grains. In the last million years or so, prevailing winds from the southwest transported these crystals and dunes formed. There are transverse, parabolic, and barchan dunes present. 

It is quite a wonderful experience to visit White Sands. You can walk barefoot and not get burned by the sand, and you can roll around in the gypsum sands without getting abraded, like you would if the dunes were made of quartz grains (hardness 7).

Photography is a challenge because of the glare. It is like photographing a snow field.

Some varieties of the mineral gypsum

I decided to do a post on the mineral gypsum just after my previous post on calcite because the two minerals can resemble each other. 

Gypsum is a very common mineral and is the most common sulphate mineral. It forms as an evaporite mineral and is commonly found in dry-lake beds. Gypsum consists of calcium sulphate dehydrate (CaSO4•2H20). If it becomes dehydrated it forms plaster of paris. 

Gypsum is very soft and can be easily scratched by a fingernail. On the Mohs Scale of Hardness, gypsum has a hardness of 2. Diamond has a hardness of 10 on this same scale. By the way, it does not fizz in acid.

This mineral is used in making fertilizers, plaster, wallboard (drywall), blackboard chalk, and some cements.

There are several varieties of gypsum, and some are shown below.
The scale in each of the three images is the same: increments of centimeters.

This is the clear (transparent) variety called selenite. It contains no significant amount of the element selenium; rather "selenite" refers to the ancient Greek word for the Moon.

This is the tabular, massive (fibrous/silky) variety called satin spar.

These five crystals show "fishtail" twins or "swallowtail" twins of gypsum. I discussed the topic of twinning in crystals in one of recent posts.

Crystals of gypsum can be extremely large in size and are the largest crystals (39 ft. = 12 m long) of any mineral on Earth. An image of these largest crystals is shown above. Note the human for scale. This image is from Wikipedia (accessed Sept. 2017) and shows the "Cave of the Crystals in Naica, Mexico" ["Cristales Cueva de Naica, México], where these enormous crystals are found.

White Sands National Monument in southern New Mexico (USA) consists of a 270 sq. mile expanse of white gypsum sand/dunes. The gypsum was eroded by way from nearby gypsum beds and deposited in the adjacent valley. As a teenager, I visited White Sands and enjoyed sliding down the dunes. The experience is much better than sliding down normal sand dunes made of quartz sand because the gypsum crystals are soft and not abasive. This image is from Wikipedia (accessed Sept. 2017).

"Desert Roses"

“Desert roses” are clusters of crystals of baryte or gypsum containing inclusions of sand. “Baryte” is the new official spelling of the mineral barite. “Desert roses” are also called “sand roses,” “rose rock,” “gypsum rose,” and “gypsum rosettes.” The clusters can be spherical shaped, irregular, or columnar shaped. They are commonly red or reddish brown.

These three pictures shown baryte "desert roses," and the largest one shown above is 2 inches in diameter. They feel heavy to the touch because of the element barium.

"Desert roses" form as evaporites when shallow waters (marine lagoons or lakes) rich in sulfates containing the elements barium or calcite precipitate out of solution. 

“Desert roses” are not that common although it seems that every collector I know has one or two. They are found in Kansas, Oklahoma, Arizona, California, Egypt, and a few other places in the world where lake beds have dried up and become evaporites. They can be of any geologic age (e.g., Permian [250 million years old] or Plio-Pleistocene [less than about 3 million years old]).

Some of the most famous and largest (up to 39 inches tall and weighing as much as 1,000 pounds) specimens of “desert roses” are from the Permian-age (about 275 million years old) Garber Sandstone in Oklahoma. In fact, in 1968, “desert roses” became known as the official state rock of Oklahoma.

Like the one shown above (1.5 inches long), not all clusters of baryte contain inclusions of sand nor do they necessarily have to form as evaporites. 

Crystals That Show Twinning

In my March 31, 2017 post concerning a distinctive granite, I showed an orthoclase crystal with twinning, which occurs when two separate crystals of the same substance share some of the same crystal lattice. Instead of a normal single crystal, the crystalline structure appears doubled. 

In this new post, I show some other common examples from my personal collection of twinned crystals. They are aragonite, pyrite, gypsum, quartz, and staurolite. 

aragonite (40 mm length)

gypsum (37 mm length)

pyrite cubes (47 mm length)

quartz (47 mm length)

staurolite (18 mm length)

pseudomorph of staurolite (40 mm)

pseudomorph of staurolite (40 mm length)

       
















pseudomorphs are formed
when a mineral is replaced
by a foreign substance