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!
REFERENCES
CITED
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.
HI, I was on a dinosaur dig on a private ranch several years ago. I found an area of hard sandstone hills. I collected many bullet shaped crystals. They were forming horizontally in the hills and falling out. Some of them were up to 10 inches long. A friend on the dig thought that they were belemnites by their shape. They were, however, inorganic.There was nothing angular about them as in pics I have seen of sand calcite. Would these be sand calcite and why do the form horizontally? Also is it legal to collect them with the ranch owner's permission? Thank you
ReplyDeleteI could probably help you if I could see some pics. Send to csrockboy at yahoo dot com. Doubt if they were sand calcite at that length. If rancher says ok, no problem. But without some photos I am guessing the may be concretions???
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