In looking at a couple of Oklahoma barite roses the other day, I was reminded of some very interesting crystals collected many decades ago. As a student at the University of South Dakota I had the opportunity to observe some great geology in the western part of the State; we were always traveling “West River” to examine rocks of virtually every geological age. During a summer tenure with the State Geological Survey, I was involved in chasing some high elevation stream gravels coming from the Black Hills and trending eastward. This ancient river is represented today by sporadic gravel deposits found on top of ridges and mesas. Since these gravels are most likely earliest Pleistocene (Pliocene?) in age (~2 Ma), their current location on ridge tops indicates much erosion has taken place since deposition. At any rate, I had the opportunity to explore and collect (with permission) at some very isolated localities in the southwestern part of the state, including Rattlesnake Butte (aka Snake Butte or Devil’s Hill) in Jackson County.
|Sandstone layer containing calcite sand crystals on the summit of Rattlesnake (Snake) Butte. Photo courtesy of U. S. National Park Service.|
The western part of South Dakota is unglaciated, is part of the Great Plains Physiographic Province, and has three very distinct regions—the gently undulating plains with a cover of short grasses, the Black Hills, and the eroded badlands. The Hills are a Laramide anticline and the easternmost range of the Rocky Mountains. Geologists often refer to the Hills as a “vest pocket” range since their footprint is small (as compared to something like the Sawatch Range in Colorado), the rocks are well- exposed, and large scale thrust faulting is absent. Precambrian rocks are exposed in the center of the anticline and successively younger Paleozoic, Mesozoic, and Tertiary rocks dip away from the dome. The best known features of the Hills include Mt. Rushmore National Park and the Homestake Gold Mine (no longer functioning as an active mine). They are also home to Wind Cave National Park and Jewel Cave National Monument while Devil’s Tower National Monument lies just outside their perimeter. Harney Peak at 7244 feet is the highest point in the Hills.
Surrounding the Hills on the plains of South Dakota, Colorado, Nebraska and Wyoming are a series of badly eroded Cretaceous and Tertiary badlands. The exposed Cretaceous rocks are primarily represented by the Pierre Shale (deep water marine), the Fox Hills Formation (near shore to beach representing the final regression of the vast Western Interior Seaway), and then a series of formations representing fluvial to deltaic to swamp to brackish water deposits such as the Hell Creek, Fort Union, and Lance. Some of these units span the Cretaceous-Tertiary (K-T) boundary and several have significant reserves of coal. The overlying Tertiary rocks include the well-known White River Group of Eocene and Oligocene age overlain by several units of Miocene and Pliocene age.
|Rocks of the White River Group exposed at Badlands National Park in South Dakota. Photo courtesy of The Virtual Fossil Museum.|
|Red Shirt Table, Shannon County, South Dakota. The White River Group forms the “badlands” in the background while Miocene age rocks cap the table. Photo courtesy of “freyawin” at http://www.panoramio.com/|
|Calcite sand crystals collected from Rattlesnake Butte several decades ago. Small crystal at bottom of photo is ~1.9 cm.|
Now, this added disclosure statement: The Rattlesnake (Snake) Butte calcite sand crystal locality in South Dakota was designated as a National Natural Landmark (NNL in 1967). The National Park Service acts as a steward for the National Natural Landmarks Program. Rattlesnake (Snake) Butte is managed by the Oglala Sioux Parks and Recreation Authority and is located on the Pine Ridge Indian Reservation. It is illegal to collect or sell fossils, artifacts and minerals on reservation land without a permit from the tribe.
So here is my suggestion---since collecting the South Dakota calcite sand crystals has been illegal since 1967 it might be wise to purchase a specimen on the open market or at your favorite rock shop. They make quite interesting display specimens and are very unique. Get them while they last!
Cirone, A. and E. Law, 2005, Microstructure of Calcite Sand Crystals and Implication on its Crystallization Process (abst.): Geological Society of America Abstracts with Programs, v. 37, no. 1, p.59.
Wanless, H. R., 1922, Notes on Sand Calcite from South Dakota; American Mineralogist, v. 7, pp. 83-86.