Tuesday, February 26, 2019


One of the “things” that I enjoy about Shannon Minerals is the great variety of rare or uncommon minerals in his stock.  So, how could I pass up a specimen of laffittite?  My initial reaction to seeing the box of specimens was---what is it?  The red and orange colors observed through the perky case certainly were attractive!  Then I read the label and noted the specimen also contained realgar [the red As4S4] and orpiment [the orange As2S3], both arsenic sulfides.  The specimen came from the Getchell Mine in Nevada, one of the more famous U.S. localities for colorful arsenic minerals.  The mine at Getchell is a Carlin-type, or sediment-hosted, replacement deposit.  The mineralization is associated with a fault zone along a Cretaceous igneous stock where hydrothermal fluids were able to deposit tiny (micron gold) flakes, or dissolved gold, into pyrite associated with Cambrian and Ordovician rocks.  The Carlin-type gold deposits in Nevada are the largest gold producing mines in the U.S.; however, since the gold is essentially invisible, the deposits are tough to locate.   The realgar and orpiment at Getchell were deposited by late stage hydrothermal solutions.

Location of Carlin-type gold deposits in Nevada. Map Public Domain courtesy of USGS.

What about the laffittite in the specimen?  If not for an XRD analysis of some tiny crystals, I would have missed identifying the mineral in the sample.  Even with this specified identification listed on the sample box, I am still sort of guessing! 

Above three photomicrographs with orpiment (O), realgar (R), laffittite (L), and an unknown sulfide (S). Width of top ~5 mm, middle 1 cm, bottom 7 mm (at lower margin.  The dark laffittite crystals are submillimeter in size.

Laffittite [AgHgAsS3] is a silver mercury arsenic sulfide associated with other late stage hydrothermal arsenic minerals like realgar and orpiment.  The Getchell Mine produces short prismatic crystals of laffittite (at other localities pseudo cubic and tabular) that are very dark red (almost appearing black) and opaque.  They have a metallic luster and a listed hardness of ~3.5 (Mohs).  Getchell crystals are often submillimeter in length. My camera is not refined enough to pick up other details of the crystals.
Arsenic minerals are often quite colorful and make good display specimens – maybe!  Exposure to bright light will alter realgar to pararealgar, and it will also decay to orpiment.  In addition, both minerals are toxic, so hand washing is a necessity. 

Every time I am able to attend the Tucson Shows I am reminded of an early 1970s tune recorded by Rare Earth (not a kind of magnet but a band!):
One, two, three, four
I just want to celebrate another day of livin'
I just want to celebrate another day of life
And so that is the way it is for me—live life today, celebrate.

Laffittite in the sky.

Friday, February 22, 2019



When the ancients moved, they left behind the buildings for a purpose.  These places are the kiikiqo or footprints.  These buildings, ashes, pottery, and petroglyphs were left to show we are connected to the Hisatsinom  (Ancestral Puebloans). 
Morgan Saufkie, Bear Clan, Hopi Tribe

Growing up I was always fascinated with history whether plants or rocks or humans.  Unfortunately, my undergraduate institution did not offer archaeology courses, or I might have majored in that particular area.  However, they did have geology and so I was off to the races.  The closest I came to working with human history was in my collecting of Pleistocene mammals in Utah—the State Archaeologist was always after me to look for butchering marks on the bones.  From my point of view, it was extremely difficult to distinguish these sorts of marks from “natural” scars.  So, I failed at this foray.  I always thought that if reincarnated, coming back as an archaeologist would be nice.

During my three summers of work (early 1970s) as a Ranger Naturalist in Dinosaur National Monument I became fascinated with the numerous petroglyphs (painted) and scarce pictographs (chipped and pecked) scattered around the land.  In fact, I tried to photograph each known glyph—both in color and in black & white.  Some glyphs were close to roads and were easy to access (but often defaced by visitors).  Others were in the back country that required hiking.  At that time in my life I could, and did, walk many miles without problems.  The color camera was a small Pentax with an over the shoulder strap.  But wait---the black and white was an old (and large and heavy) 4 x 5 (inches) piece of work with really great optics.  It also needed to be mounted on a cumbersome (and heavy) tripod where the “picture taker—me” loaded the negative, threw a black cloth over my head and camera, and focused, pushed the timer button, carefully took out and protected the negative, and moved on.  Back at the quarry I developed and printed the back and white negatives.  The optics, plus the large negatives, allowed “really large” enlargements!  I often wonder if the monument achieves still have those photos.
The famous lizard petroglyph at Dinosaur National Monument.
Since my stint with the Park Service I have always tried to visit older Anasazi sites, mostly near paved roads, during my many trips to the Mountain West.  But wait—sometime in the past decades I learned the term Anasazi should be replaced by the term Ancestral or Ancient Puebloans.  It seems the Navajos (Dinè) told the early non-Native American explorers and traders the Anasazi (meaning ancient enemies) constructed the numerous abandoned pit houses and pueblos---and the name stuck until recently. 
I am an avid reader of Mountain West history and long ago decided that Hovenweep National Monument, northeast of Bluff, Utah, was on my Bucket List.  The Monument is one of those places that is a destination point and not a “dad, let’s pull off to see the Indian ruins as I need to potty.”  One needs to “be going” to Hovenweep in order to get there! 
Map, courtesy of USGS, showing location of Hovenweep National Monument northeast of Bluff on the Utah-Colorado State Line.
So, off we go through a narrow canyon leaving the cozy campground at Bluff (see Post July 18, 2018) and heading north towards Blanding, Utah, on U.S. 163.  The summit of the canyon is a broad plateau held up by the Jurassic Bluff Sandstone (which may be a local stand-alone formation or a local member of the Morrison Formation).
The Bluff Sandstone forms a narrow canyon along the highway leading out of Bluff and also is the caprock of a broad plateau at the summit.
After about 10 miles of travel Utah 262 takes off to the right (east) heading to Hovenweep; follow the signs and don’t wander off. Along the way there are a few outcrops of Late Jurassic Morrison Formation; however, the roads traverse mostly on the overlying  Cretaceous Dakota Formation.  This highland is part of the Great Sage Plain, named not for a geomorphic expression of landscape but for a plant, big sagebrush (Artemisia tridentata).  The Plain ranges in elevation from about 7000-5000 feet and is part of Colorado Plateau Physiographic Province. The Plain stretches from near Monticello and the Abajo Mountains (north of Blanding) southeast to the San Juan Mountains in southwestern and is home to the largest concentration of Ancestral Puebloan structures in the U.S.  The Cajon Mesa is a particular subsection of the Plain and is the location of Hovenweep.

What attracted these early Americans to Cajon Mesa?  Well, the same thing that attracts farmers to land today—water and soils capable of growing crops.  But I could say that geology attracted the Ancestral Puebloans.  Soil developed on the Plain via wind-blown sand and clay (termed loess) and probably was associated with winds from the southwest during the last 10,000-12,000 years.  These loessal soils can be quite rich when water is available.  On the Cajon Mesa the Dakota Formation (Cretaceous) forms the upper rimrock and is composed of sandstone and mudstones with a few beds of poor coal. The Dakota is a mixture of stream, swamp and maybe some beach sands as the unit represents an initial transgression of marine waters onto the continental western interior.  In fact, we term this great inland sea the Western Interior Seaway and it stretched from Utah to Minnesota and Missouri and from Alaska to the Gulf of Mexico. 
Dakota Formation, the caprock at Hovenweep.
Below the Dakota Formation is the Burro Canyon Formation, also of Cretaceous age but older than the Dakota, that is composed of a variety of  braided stream-deposited rocks: conglomerate, sandstone, shale, mudstone, limestone and tightly cemented quartz sandstone (wrongly termed quartzite).  So, when water does arrive in the form of summer monsoon rains or winter snows it gathers in pot holes on the rimrock massive sandstone, or seeps into and through the Dakota rocks until it reaches the Burro Canyon, a rather impervious layer.  At that point the water begins to move horizontally and when it reaches the canyon at Hovenweep it forms seeps or springs.  The inhabitants were then able to capture the water by use of dams. 
On Cajon Mesa the Ancestral Puebloans constructed terraces to funnel rain water and dams to catch the water so that crops (mainly corn, beans and squash) could be irrigated. The inhabitants were farmers rather than hunters-gathers that preceded them.
The Burro Canyon Formation underlies the Dakota Formation at Hovenweep.  Part of the formation is a very indurated conglomerate.  Photo courtesy National Park Service.
Geology also played other important roles.  For example, the sandstone layers in the Dakota provided the masonry blocks for construction of the towers and buildings.  Some of the conglomerate beds in the Burro Canyon contain numerous chert and flint cobbles that provided material for projectile points.
Masonry blocks used to construct the buildings at Hovenweep were quarried from the Dakota Formation--without the aid of steel chisels to shape.
The six groups of masonry structures at Hovenweep were constructed by Ancestral Puebloans who first settled in the area ~500 A.D. and farmed portions of the Cajon Plateau and parts of the inner canyons (hunters and gatherers, temporary residents, were probably in the area ~8000-5000 BC until the Ancestral Puebloans arrived ).  As noted above, they built terraces and water dams and granaries; the latter storage areas were in the canyon to better protect crops like corn.  But as the population soared (~2500?) , workers needed to travel further away “from their canyon home” to collect wood and plant/harvest crops.  Archaeologists believe the population peaked between 1200-1300 A.D. and soon after that they, like the inhabitants of Mesa Verde and other living centers, left the area to start a new life in the Rio Grande and Little Colorado River valleys.  Researchers are uncertain about this move but suspect drought, warfare and overpopulation.  Does this ring a bell today? 

As a native Kansan I often wonder if the population of western Kansas will decrease significantly when irrigation waters of the Ogallala Aquifer are depleted?  What happens when  Lake Mead on the Colorado River cannot  provide enough water for the agriculture and growing population of California and Arizona?  Should valuable water of Arizona be used to irrigate cotton and alfalfa in the desert?  Where will the people of Syria go since their country's infrastructure is essentially destroyed? As climate change moves forward where will large populations along the U.S. coasts migrate (after being flooded out from rising sea level)?  Maybe Elon Musk will take us to Mars!
Tower Point Ruin. We come here to visit our ancestors.  They are all around. (Victor Sarracino, Water Clan, Pueblo of Laguna)
Twin Towers. Through the strength of the spirits, our ancestors built these dwellings here (Ernest m. Vallo, Sr., Eagle Clan, Pueblo of Acoma).

Montezuma Castle.  Photo courtesy National Park Service.
One of the great views at Hovenweep is to the east and of Ute Mountain or Sleeping Ute Mountain not far over the line in Colorado.  Like other isolated mountain ranges (~12 x 5 miles with a topographic relief of ~4000 feet and an elevation of ~9984 feet) in this section of the Colorado Plateau, Sleeping Ute Mountain is a laccolithic range---overlying sedimentary rocks have been domed up by the rising igneous magma and then the less-resistant rocks were eroded.  Unlike the other Plateau mountains such as the Henry Mountains, the Abajo Mountains and the La Sal Mountains, the Sleeping Ute Mountain was intruded into overlying rocks in the Late Cretaceous ~72 Ma.  The other ranges are much younger, perhaps ~25-28 Ma in the Tertiary.  The name comes from the profile of a Ute warrior lying on his back with his arms folded.  Sleeping Ute Mountain is not on a “main road” and is situated inside of the Ute Mountain Ute Reservation and plays a role in some of their ceremonies.
Sleeping Ute Mountain as viewed from Hovenweep.  Dakota Formation as caprock.  Photo courtesy National Park Service. The Hopi name for Sleeping Ute Mountain is Hon tsomo or Bear Mountain (Consensus of Elders, The Hopi Tribe).
President Warren G. Harding was correct when in 1923 he established a national monument preserving the amazing structures built by a group of Ancestral Puebloans. Many readers may have visited the structures at nearby Mesa Verde National Park (established 1906) but if travelers are in the area get a map and take the detour to Hovenweep National Monument.  It is a great place to learn how these ancient Americans understood geological processes and used them in their everyday living.  It is an amazing place and I can check it off my bucket list!