VIVIANITE FROM FLORIDA SEDIMENTARY ROCKS AND BLUE DEAD BODIES

 

Vivianite is a hydrated iron phosphate mineral [Fe₃⁺⁺ (PO₄)₂-8H₂0] that is a crystal of many colors, and in fact, can change color over its lifetime. Freshly exposed vivianite is generally colorless but with time oxidizes to green to bluish green to blue crystals.  Continued oxidation of the iron from Fe⁺⁺ (ferric) to Fe+++ (ferrous)  will produce crystals so dark blue they appear black.  Many crystals have a vitreous luster although they can grade into pearly or dull specimens.  Colorless crystals are transparent while lighter colored specimens become translucent and massive specimens generally are rather opaque. As with the color, mineral streak ranges from colorless to various shades of blue. Vivianite is quite soft, ~2.0 or less (Mohs).  The best “showy” specimens have prismatic (elongated along the C Axis) or flattened/bladed (along the B Axis) crystals and often form in stellate cluster; however, there are a variety of other morphological forms.

Vivianite is thought to occur as: 1) as a secondary mineral in metallic ore deposits; 2) in pegmatites as an alteration product of primary phosphate minerals; or 3) as a mineral associated with the phosphate found in sedimentary deposits. However, Petrov (2008) noted the mineral is not characteristic of the oxidized zone but of “deep unoxidized levels of ore deposits.” Most vivianite specimens collected in the western states, or observed in rock and mineral shows, are secondary in nature or from the phosphate minerals in  pegmatites.  Collected specimens, when first exposed to sunlight and oxygen, are often a beautiful blue and prismatic along the C-axis.

Very rarely do Colorado rockhounds come upon vivianite collected from organically rich unconsolidated clays and other sediments/rocks (mostly Cenozoic in ages). In the U.S. most of these sedimentary vivianites come from the Central Florida Phosphate District (AKA Florida Platform) where iron and water, along with original phosphatic material, has allowed vivianite to form: Fe₃⁺⁺ (PO₄)₂-8H₂0. The original phosphorus is thought to have been derived from precipitation in marine waters, and from the skeletons/shells and the waste products  of animals living in these waters.

The basement rocks of the Florida Platform are a fragment of the African Plate that remained attached to the North American Plate when rifting occurred in the Jurassic and range in age from late Precambrian-early Cambrian to mid-Jurassic (Barnett 1975).

A sedimentary sequence rests uncomfortably on top of the basement rocks, and is composed of Middle Jurassic to Holocene evaporite, carbonate, and siliciclastic sediments. This sedimentary sequence is the result of deposition on the relatively stable, passive margin of the North American Plate (Scott, 1989, 2016).

During the Cenozoic concentrations of silt to sand-sized phosphate pellets, mixed with carbonates and clastic sediments, were deposited in shallow water environments over much of the Florida Platform, in a broad range of carbonate and clastic sediments. During the Miocene and Pliocene phosphate was particularly concentrated in several basins in the Central Florida Phosphate District and these were the areas where a major phosphate industry begin development in the late 1800s. By 1893, production had expanded to 1.25 million tons and Florida became the world's leading producer of phosphate for the next century. By 2015/2016 the U,S, had dropped to the 3^rd largest producer of phosphate behind China and Morocco and production had expanded from the “Eastern Phosphate Fields”  of Florida and North Carolina to the “Western Phosphate Fields” of Utah and Idaho. However, in 2021 Florida still produced ~75% of the U.S. production of ~24 million tons. The Eastern Field operations use open pit mining to extract the ore from Miocene and Pliocene sediments/rocks. The Western Fields mine phosphate from limestone in the Permian Phosphoria Formation (Scott, 2016).

A well-formed, terminated crystal of glassy and gemmy, blue-green, vivianite, ~4 mm in length, collected from Clear Spring Mine, Homeland, Central Florida Phosphate Mining District, Polk Co., Florida. Light patch is carbonate matrix. A backlight would show transparency. Collection of Art Smith 1980.

REFERENCES CITED

Barnett, R. S., 1975, Basement structure of Florida and its tectonic implications: Gulf Coast Association of Geological Societies Transactions, Vol. 25.

Hurst, M. V. (Ed.), 2016, Central Florida Phosphate District Third Edition: Southeastern Geological Society Field Trip Guidebook No. 67.

Scott, T.M., 1989, The Geology of Central and Northern Florida with Emphasis on the Hawthorn Group, in Scott, T.M., and Cathcart, J.B., AGU 28th International Geological Congress, Field Trip Guidebook T178.

Scott, T. M., 2016,  Geologic overview of Florida in Hurst, M. V. (Ed.), Central Florida Phosphate District Third Edition: Southeastern Geological Society Field Trip Guidebook No. 67.

Virtually everything you might want to know about Florida phosphate may be found in the Hurst guidebook referenced above and available as a PDF file: http://www.segs.org/wp-content/uploads/2010/01/SEGS-Guidebook-67.pdf

 

AND NOW FOR THE REALLY INTERESTING STORY FROM CHRIS DRUDGE October 25, 2016 at: The Vivid Blue Mineral That Grows on Buried Bodies and Confuses Archaeologists - Atlas Obscura

IN 1861, a railway engineer by the name of John White passed away, was buried in a cast iron coffin, and began a slow transformation from White to blue.

The explanation for this spooky color change, which has occurred on numerous occasions all over the world, lies in the composition of the human body. Among the molecules contained within us is phosphate, a central phosphorus atom bound on four sides to atoms of oxygen. Phosphate is present in the hard bits of bones and teeth (as part of the mineral hydroxylapatite), helps hold together strands of DNA and RNA, and is used by cells to store and move energy around as well as to organize their many protein-driven activities.

If a dead person ends up buried somewhere waterlogged, lacking in oxygen, and loaded with iron, the phosphate leaking from their decaying remains can slowly combine with the iron and water to form a mineral called vivianite. It starts out clear and colorless, but will rapidly turn progressively darker shades of blue upon exposure to air as the iron within it reacts with oxygen. The formation of vivianite (also known as blue ironstone) is helped along by bacteria which act to dissolve iron out of soil and phosphate out of bodies while also directing the growth of the blue crystals. 

In the case of Mr. White, in keeping with the styles of the time, his coffin had a glass window installed in the front so his face could be seen by mourners when the lid was shut. At some point after burial, the glass had broken, allowing groundwater to seep inside and react with the cast iron coffin and phosphate-rich body. The end result was a corpse surround by blue vivianite crystals, revealed when the coffin was exhumed as part of an archaeological rescue excavation over a century after being buried.

 

 

THEISITE: Just because you don't understand it doesn't mean it isn't so.

I am always on the lookout for funky and sort of quirky uncommon to rare minerals. My small mineral collection has numerous specimens that I purchased due to the facts that I did not recognize the name, and it was cheap. Anything coming off of a dusty shelf with an older label was a bonus. An extra, extra bonus was created if the new mineral was collected in Colorado. And a three-level bonus appeared if the mineral came from near Tuckerville, Colorado, a town, well really a former town now inhabited by ghosts. After purchasing a three-level bonus mineral I didn’t have the slightest idea about the location of Tuckerville until I noticed it was close to Vallecito Reservoir. That particular body of water, on the Pine River, is located about 18 miles northeast of Durango. I have camped there twice in absolutely beautiful USFS campgrounds and spent the time fishing rather than exploring back roads. Tuckerville is then located about 12 miles northeast of the Reservoir on FS 2274 or Middle Mountain Road, a winding road that feels better in a 4-wheel drive pickup than a low-slung passenger car. The elevation is ~ 10,600 feet. After speaking to the ghosts of “almost nothing left” Tuckerville, rockhounds must take a hike (400 feet elevation gain) on the established “jeep trail” to reach the old mines of Tuckers Tunnel or Tuckerville Prospects. Evidently the tunnel has collapsed as have other adits. Mineral collectors who made it this far have zeroed in on what remains of the Tunnel dump. MinDat lists 31 valid mineral species collected in the dump and noted the Tunnel dump as the Type Locality of theisite [Cu₅Zn₅(AsO₄,SbO₄)₂(OH)₁₄].

WORDS OF THE DAY

Funky Mineral: Theisite

Ghost Town:  Tuckerville

New Geological Term to Learn:  Fahlore Deposits

There is not much to say about the Tuckerville Prospects except I regret not being able to visit the locality (at the time of camping at Vallecito I was chasing fossils). Very little information, at least that I could locate, is published on the mining area. Certainly, the best publication is a Rocks and Minerals article by Haynes and Paul Hlava (1998). In addition, Williams (1982) described theisite as a new mineral in Mineralogical Record; however, I could not locate a copy of that article but did find the abstract.

Google Earth© image of the location of Tuckerville (nothing to see on image) and the Tuckerville Prospects.  The winding road comes north from Vallecito Reservoir.

According to Haynes and Hlava (1998) the Tuckerville Prospects are part of the Cave Basin Mining District where in 1913-1914 speculators and investors were overly optimistic about future production of copper, silver, and gold—many claims were filed but production was minimal. As best I can determine in adding figures together, the Cave Basin mines, mostly the Mary Murphy, Holbrook, and Silver Reef, produced a tad less than 100 ounces of gold, ~270 ounces of silver, ~2900 pounds of copper, and ~1700 pounds of lead---all from ~120 tons of ore shipped (via animal drawn wagons or mule trains????) down the mountain to an unknown processing plant. Mining was sporadic from 1913 to 1936. The above production figures are from Schmitt and Raymond (1977) and Steven and others (1969).

I may be missing something but have been unable to locate base metal production figures for the Tuckerville Prospects (the above production figures are from the entire District).  However, it must have been minuscule. The minerals listed by MinDat do not include silver or gold; however, some minerals do include copper, mercury, zinc and maybe a grain or two of galena (lead). Theisite was discovered in 1980 at Tucker Tunnel by two geologists, N.J. Theis and Michael Madsen (Theis and others, 1981), as they tromped through the area looking for uranium—evidently there are some rocks that excite a Geiger Counter, perhaps uraninite and/or zeunerite, as Haynes and Hlava stated, “the prospect [Tuckerville] is radioactively anomalous (up to 700 gamma counts per second).” Steven and others (1969) noted that “base and precious metals in the Cave Basin District were replacement deposits in lower Paleozoic sedimentary rocks”—perhaps the Ouray of Leadville formations.

Now down to the new mineral from Tucker Tunnel—theisite, a copper zinc arsenate antimonate. We know the chemical makeup of the mineral due to analyses by X-ray Powder Diffraction and Electron Microprobe studies. Unfortunately, I don’t have either gizmo in my office.

Visually (with a microscope) theisite is very difficult to identify, especially for an ole plugger like me. First of all, specimens are usually quite small (mine are really, really tiny) and rarely occur as crystals but as crusts, spherical aggregates or simply individual spheres, cleavage plates, micaceous plates, or just plain globs. The color is some sort of blue + green: greenish blue, turquoise-green, turquoise-blue, pale green, or pale blue. Specimens have a pearly luster and are very soft (MinDat states 1.5 Mohs).  I found it very difficult to identify my small specimens and if not for the collection and identification by David Shannon I could have guessed any number of copper zinc minerals.

Two dark green spheres of theisite and two lighter green spheres of "your guess." The dark mineral is a manganese oxide. Width FOV ~4.0 mm. 

Green to blue green theisite spheres or cluster of spheres in and around a vug. Width FOV ~4.0 mm.

Scattered green to blue green theisite spheres or cluster of spheres. Width FOV ~3.0 mm. 

Clear gemmy crystals of platy hemimorphite with black manganese oxide. Width FOV ~2.0 mm. 

MinDat pointed out that theisite was a rare secondary mineral in fahlore deposits. Well, that piece of info rattled my brain and sent me scrambling. The best I could do with an understanding definition of fahlore was from Wikipedia: Fahlore refers to an ore consisting of complex sulfosalt minerals (a metal + semi-metal + sulfur) and in the case of theisite the mineral is formed due to oxidation of a mineral(s) in the tennantite--tetrahedrite solid solution series.

Just because you don't understand it doesn't mean it isn't so.

            Lemony Snicket

REFERENCES CITED

Haynes, P.E. and P.F. Hlava, 1998, Mineralogy of Tuckers Tunnel: Tuckerville, Hinsdale County, Colorado: Rocks & Minerals, vol. 73, no. 5.   

Schmitt, L. J. and W. H. Raymond, 1977, Geology and mineral deposits of the Needle Mountains district, southwestern Colorado: U.S. Geological Survey Bulletin 1434.

Steven, T. A., L. J. Schmitt Jr., M. J. Sheridan, and F. E. Williams, 1969, Mineral resources of the Sun Juan primitive area, Colorado: U.S. Geological Survey Bulletin 1261-F.

Theis, N. J., M. E. Madsen, G. C. Rosenlund, W. R. Reinhart, and H. A. Gardner, 1981, National uranium evaluation, Durango quadrangle, Colorado, Grand Junction, Colorado: Bendix Field Engineering Corp.

Williams, S. A. 1982, Theisite, a new mineral from Colorado: Mineralogical Magazine, vol. 46.

PERHAMITE, A RARE PHOSPHATE FROM MAINE

 

Although I enjoy collecting minerals, especially phosphates, in the pegmatites of the Black Hills of South Dakota I often wish the rocks of Maine were a wee bit closer to my home in Colorado! Since the journey is more than a day trip I am left with purchasing specimens found at rock and mineral shows, a good alternative. Interestingly, to an ole softrocker like me who spent most of his professional career looking for fossils in Mesozoic and Cenozoic outcrops, rocks of Maine generally lack exposures of these ages except for scattered small igneous intrusions and dikes of Mesozoic age. Maine rocks are Precambrian and Paleozoic (mostly Cambrian through Devonian) in age with a covering of unconsolidated sediments left behind by Pleistocene glaciers. The latter seems to support a heavy growth of trees and undergrowth that often inhibits the discovery of the underlying bedrock. However, there are many “stone” quarries around the state that have allowed geologists and rockhounds to collect a bonanza of interesting minerals and gems.  Geology.com noted that the first commercial gemstone mine in the U.S. dates back to 1821 when gem tourmaline was collected near Paris in a pegmatite on a hill known as Mt. Mica.  That mining has continued to the present. Most Maine collecting localities are in pegmatites scattered across the state (especially in the counties of Oxford, Androscoggin, and Sagadahoc ---AKA Maine Pegmatite Belt) that offer rockhounds and geologists opportunities in both commercial mines, such as Poland Mining Camps, and in abandoned quarries.  In addition, there is the Maine Mineral and Gem Museum in Bethel containing stunning displays, and also housing the Mineralogy, Petrology, and Pegmatology Research Group. The latter entity “focuses on exploring the pegmatites of Maine and their associated minerals.”

One of the most studied pegmatites in Maine is the Emmons Pegmatite found on Uncle Tom Mountain in Oxford County where beryl and other minerals were found in the early 1900s and first mined for feldspar in the 1930s; however, that venture was rather short-lived due to the long distance of the mine from a processing plant.  Early mineral collecting enthusiasts then started extracting beryl and ultimately collected about 5000 carats of gem morganite (pink beryl); however, specimen mining did not really take off until the late 1900s.; ---see the complete collecting and mineral story in Falster and others (Rocks and Minerals, v.94, no.6).

One of the interesting minerals from the Emmons that popped up in rummaging through my collection (from a purchase several years ago) was the phosphate perhamite [Ca₃Al_7.7Si₃P₄O_23.5(OH)_14.1-8H₂0], a specimen originally collected by Micromounter Hall of Fame member Gene Bearss.  The mineral is a rare calcium aluminum silico-phosphate that usually is found as isolated small spherules in late-stage pegmatite vugs. The Bearss specimen (photo below) shows the common morphology--a spherical aggregate of subvitreous hexagonal plates. Falster and others noted that perhamite from the Emmons pegmatite ranks among the finest examples of this species. Width of the spherule is ~1.0 mm.