SOAPSTONE: WARMING THE TOES

 

To get away from one's working environment is, in a sense, to get away from one's self; and this is often the chief advantage of travel and change.— Charles Horton Cooley

Check out my furry friend, a frequent visitor looking for, but never finding, a snack.  I could not load the security camera video so this is a snapshot as he was heading to the small front porch. I think he said, I hear there is a Bear Market on Wall Street? Got any rotten meat around here?

Noted in my last posting was the fact that I was sort of coming out of dormancy and getting my mojo back—after spending a couple of months traveling, reading, watching Spotted Towhees scratch around in the “wild part” of my yard, and checking out the Black Bears visiting the front yard in the evening.  Might not seem too exciting; however, relaxing it was.  Now I have a pile of minerals that need to be examined in greater detail. And I found out that not all interesting minerals need to be purchased from a rock/mineral store or collected from outcrops!  Case in point: I was rummaging around my Cabinet of Natural Curiosities and came across a green/gray slab of rock with a handle.  I remembered that it came from a farm auction in rural Missouri (early 1990s) and since no other person bid, and the auctioneer knew I was a sucker for strange gadgets, gaveled it down for Mike at a buck. At least I knew what it was—not the case with several of my auction gadgets.  

The sawed and polished slab is an old warmer that people used to heat their beds and buggy floors as a way to help keep their feet warm.  Since these gadgets were extremely popular in the 1800s (in the U.S.) they predated anything related to heaters found in vehicles with internal combustible engines.

These footwarmers were made from soapstone, a rock that has been used for centuries as a medium for carvers—from small ornaments to eating bowls to large art pieces. A metamorphic rock, soapstone is essentially a “dirty talc.”  That is talc, a [magnesium silicate [Mg₃Si₄O₁₀(OH)₂] is included with several other minerals such as chlorite and various amphiboles. It is sort of a “mixed up rock” with a variable chemical composition (the amount talc ranges from ~30% to ~80%) that formed during the metamorphism of ultramafic rocks (such as dunite and Serpentine Group minerals) along subsiding plate boundaries.

Since soapstone is “sort of” a massive variety of talc with included minerals, the physical characteristics vary. Colors of massive talc range from colorless to white to shades of gray, green and brown.  Soapstone is usually a gray to greenish gray color with foot warmers often displaying a dark patina due to various episodes of heating. Both massive talc and soapstone have a waxy to greasy luster and feel slick or soapy. Talc is listed as the softest mineral on the Mohs scale coming in as number 1. However, soapstone, with its variable composition of included minerals, also has a variable hardness.  Soapstone mined and cut into countertops, tile, and other architectural items has ~30% talc and hardness ranges up to ~5 (Mohs). Carving soapstone may have ~80% talc and a hardness of ~1-2 (Mohs). Although talc is often called soapstone (due to the soapy feel), strictly speaking they are different as talc is a mineral while soapstone is a rock with a variable composition (but always including talc).

Soapstone and massive talc, usually known as steatite, have been used by various civilizations for centuries. The softer steatite was usually carved into various ornaments while the harder soapstone was used for bowls and cooking pots, oil lamps, smoking pipes, grave markers and a variety of other items. Soapstone and steatite have played a major part in the lives of people on every continent for millennia.  It is easy to carve (statues), is durable (bowls), has a high heat storage capacity (footwarmers), is heat resistant (bowls of smoking pipes keep cool), and has unique electrical characteristics (used for insulation of electrical wiring and components). Soapstone, and steatite, seeming a simple mineral/rock to most is actually quite wondrous.

Soapstone footwarmer with metal handle. U.S. quarter for scale.

And that brings me back to soapstone footwarmers. Almost all footwarmers seen in museums and antique stores are slabs of soapstone (not softer steatite), greenish gray to gray in color, about 10 inches by 7 inches by 1 inch in size with a metal handle.  The most coveted by collectors are those with an original cloth (linen) sack covering. As for the original source of the soapstone in my collection---hard to tell as the specimen lacks factory marks. In the U.S. there have been large soapstone mines in Pennsylvania, Vermont, Virginia, and Massachusetts—take your pick.

KEEPING THE TOES WARM

Mizzou farm auction

A green soapstone gavels down

Old time footwarmer

CELEBRATING GRUNERITE FROM YOOPERLAND

 

The Colorado Springs Mineralogical Society (CSMS) celebrated 2022 by holding their annual (except for a Covid postponement) Pikes Peak Gem, Mineral, and Jewelry Show.  As best I could count (a little tough after 10 fingers), 56 vendors were present at the Norris Penrose Event Center.  In addition, ~14 exhibits displayed a variety of minerals, fossils, and gems. The Colorado Gold Panners had a couple of panning troughs filled with sand, gold, and nifty minerals that attracted a variety of participants from 2-100 years old or so. The local Florissant Fossil Beds National Monument represented the Bureau of Land Management, the U.S. Forest Service, and the National Park Service.  David and his crew of workers spent three days trying to attract new members into the CSMS Pebble Pups and Earth Science Scholars programs by displaying everything a kid might be interested in, including dinosaurs. And finally, the Silent Auction, the most popular table in the Show, sold hundreds and hundreds of specimens to children and adults alike—everyone went away from this activity happy. Congratulations to Show Chair Lisa and Prez John who recruited a great cast of volunteers.

Open the doors and let in the crowd. June 2022 CSMS Show at Norris Penrose Center in Colorado Springs.
 

My prior commitments kept me out of the Show except for a couple of short stints; however, the attendance seemed pretty amazing.  People are tired of staying home due to Covid and what better activity to “get them out of the house” than visiting displays of fantastic rocks, minerals, fossils, and gems.  

I did find a few specimens that made it home to my cabinet of curiosities, but nothing that a curator/curatrix would display in the Natural History Museum.

I decided to increase my collection of minerals from the Northern Peninsula of Michigan—Yooperland as I noted in several other postings.  One of the more interesting acquirements from D’Angelos down in Trinidad was an amphibole known as grunerite.  The first question that may come to a reader’s mind is, “what is an amphibole.”  My answer is pretty vague as identifying an “amphibole” in my beginning Physical Geology class was confusing to say the least.  Amphiboles have now been elevated to Supergroup status by the International Mineralogical Association and contain two Groups divided into several Subgroups and a plethora of individual minerals.  Amphiboles are silicate minerals containing SiO4 tetrahedra with cations of iron and/or magnesium—plus a variety of other minor constituents.  Individual minerals often form prismatic or needle-like crystals and may crystallize in either the Monoclinic or Orthorhombic Crystal Systems.  In addition, amphibole minerals may form in either igneous or metamorphic rocks; hornblende may be the “best known” mineral.

My confusion in Physical Geology, and later Mineralogy, was usually due to the confusion of amphibole minerals with the similar looking pyroxene minerals such as augite.  Competent mineralogists will gently explain that amphiboles contain, in their atomic structure, a double chain of tetrahedra while pyroxenes have a single chain, and that amphiboles contain either hydroxyl (OH), fluorine (F), or chlorine (Cl).  Try explaining that to a beginning geology student still licking clear specimens trying to identify halite or calcite! So, we were taught to identify minerals of the two groups by examining cleavage angles.  Amphiboles cleave at an oblique angle, about 120 degrees, and pyroxene cleavage fragments are about 90 degrees and almost form a "square".

Grunerite is a common mineral if located in metamorphosed iron formations, and occasionally in other metamorphic rocks.  It is an iron rich amphibole [(Fe₂)(Fe₅)(Si₈O₂₂)(OH)₂] in solid solution with the magnesium (replacing the iron) rich cummingtonite (also a metamorphic mineral). As far as I can determine there are no named minerals between cummingtonite and grunerite. Hawthorne and Oberti (2006) defined the boundary as Mg:Fe=1:1.

Different views of grunerite sprays in black magnetite. Length top ~7.7 cm.  Bottom ~6.6 cm.
 

Grunerite from Yooperland occurs as bronze to brown to brownish green to gray metallic bundles or radiating sprays of acicular or prismatic crystals.  It is difficult to determine but crystals have a hardness of around 5-6 (Mohs), a vitreous luster but a colorless streak. Rockhounds usually identify grunerite as the radiating sprays found on Banded Iron Formations. My specimen came from the Precambrian Bijiki Schist (Iron Formation) near Michigamme Lake in Marquette County, Michigan, and sprays are intimately associated with black magnetite.  I saw minor amounts of quartz in the specimen but could not locate garnets nor biotite nor chlorite (at times common associates). Heinrich (2004) described the Marquette Iron Ranges as former siderite-chert rocks now metamorphosed to grunerite-quartz + magnetite.

 

Photomicrographs of acicular crystals of grunerite and sub-millimeter crystals of black magnetite. Width middle and bottom ~1.6 cm.

REFERENCES CITED

Hawthorne, F.C. and R. Oberti, 2006, On the classification of amphiboles: The Canadian Mineralogist Vol. 44.

Heinrich, E.W. (with updates and revisions by G.W. Robinson), 2004, Mineralogy of Michigan: Michigan Technological University, Houghton.

 CELEBRATION OF A MINERAL

Beneath the earth’s crust
Hot metamorphic terrain
Grunerite forming  

 For those readers who might have missed me (no posts for a couple of months), I have been in a state of aestivation, a period of dormancy where my writing has been inactive and has been replaced by the relaxation of reading causing a lowered metabolic rate. Much of the reading has been non-geological in nature in my quest to continue as a lifelong learner.  I even brought out one of my ancient lit class assignments (John Keats) and dwelled on the final stanza: 

When old age shall this generation waste,

                Thou shalt remain, in midst of other woe

Than ours, a friend to man, to whom thou say'st,

         "Beauty is truth, truth beauty,—that is all

                Ye know on earth, and all ye need to know.

 

 

 

MONTROSEITE: A COLORADO NATIVE

 

The Tucson shows are “done gone” and were a big success, at least from my point of view.  I was able to spend every day for two weeks exploring the different venues and making a purchase or two.  The Tucson “main show” occupied two full days of my time trying to digest the exhibits and ogling at the many specimens offered to buyers.  In addition, I spent several hours over 4 days up at the Mineral City event as documented in recent Posts.  In moving on from the venues at Mineral City I next visited what is probably the most authentic show left in Tucson, the Miners Co-op Rock Show located west of I 10 at Mike Jacobs Sports Park.  When I say authentic, I mean what many venues looked like several decades ago---grass and gravel, free parking, vendors selling from pickup beds, tents, open air tables, small trailers, cooking meals over a small propane stove, and living quarters in small RVs parked directly behind their displays.  The rains come and tarps or plastic unfurl to cover the tables.  Here comes the welcome sun and off come the covers.  There seems to be a camaraderie among the dealers, and all seem very willing to spend time visiting with the lookers and buyers.  I usually see the same dealers every year including CSMS members Kim and Bodie from Runnin Boar Minerals selling locally derived amazonite from their mines.

 

Outside sellers at Miners Co-Op Rock Show: minerals, rocks, fossils, doodads, and free conversations with nice, home-town people. 
 

Black montroseite mixed with corvusite on the surface and in pores of quartz-rich sandstone. Width FOV ~5.0 cm.

Photomicrographs of above specimen. Width FOV top ~5mm and bottom ~9 mm.

I did not find many specimens to tweak my interest but did come home with a specimen of an ugly black mineral collected from one of the uranium-vanadium mines on the Colorado Plateau.  Without looking at the label I thought it probably was corvusite, a nondescript hydrated sodium, calcium, potassium, magnesium, iron and vanadium oxide (and also pretty ugly): (Na,K,Ca,Mg)₂(V⁵⁺V⁴⁺Fe²⁺)₈O₂₀--6-10H₂O  [For a better description see November 10, 2019 posting].  However, my purchased specimen (black to grayish black) was identified as montroseite, a vanadium iron oxide hydroxyl [(V³⁺Fe³⁺)O(OH)] or sometimes labeled as a vanadium oxide [V³⁺O(OH)].  Although these two minerals, corvusite and montroseite, might look similar, and they are often intermixed in a single specimen, the iron in corvusite is ferrous iron with a charge of 2+ while montroseite is the 3+ ferric iron.  In addition, corvusite has water, H₂O, while montroseite has a hydroxyl molecule. The vanadium in corvusite has charges of both 4+ and 5+ while montroseite has 3+ vanadium.

Reverse of above specimen showing, what appears to be, massive, bladed crystals of montroseite.  Width field of view ~1.0 cm.

My specimen was collected from the Burro Mine, Slick Rock District, San Miguel County, Colorado [the Type Locality of 12 minerals].  In fact, the reason I purchased the specimen is that montroseite is a Colorado Native as the Type Locality is the Bitter Creek Mine, Uravan Mining District, Montrose County, Colorado [located just north of the Burro Mine in San Miguel County] (Weeks and others, 1951, 1953).

Montroseite is tough to identify without some gizmo like XRD.  It is black to gray black in color with a black streak and a less than metallic luster (sort of a dull metallic).  It is fairly hard at ~ 6.0 (Mohs).  If one can locate crystals, they might be bladed and or striated.  Unfortunately, I have had an extremely difficult time locating good crystals as the vanadium minerals present in/on the sandstone matrix are massive or seem to fill tiny pores between the grains of sand (essentially quartz).

Here is another problem that I can’t fix without an XRD. Montroseite seems to rapidly transform to paramontroseite {V⁴⁺O₂] when exposed to air—paramontroseite is a pseudomorph after montroseite, and also has its type locality at the Bitter Creek Mine. Paramontroseite results from the oxidation of montroseite in a solid solution relationship. Oxygen, either in groundwater of in the air, oxidizes montroseite in temperatures under 50 degrees Celsius and the hydrogen escapes: 2V³⁺O(OH) + 1/2O₂à2V⁴⁺O₂ + H₂O (Evans and Mrose, 1955).

But then, paramontroseite is also unstable and weathering causes numerous other minerals to form, depending upon chemical weathering conditions: mostly corvusite but also hewettite, hummerite, pascoite, rossite, and simploite (Garrels and Pommer,1957). When montroseite “changes” to paramontroseite the crystal structure essentially remains intact.  When paramontroseite weathers its crystal structure is destroyed and new minerals form.

The exact source of the original vanadium in these deposits is somewhat uncertain; however, Thamn, Kovschak and Adams (1981) noted the “Salt Wash [Member of the Jurassic Morrison Formation] deposits are essentially vanadium deposits, but as yet no convincing case has been made for the source of that vanadium. Favorite hypotheses suggest that it was (a) derived from altered llmenite and magnetite, (b) introduced diagenetically from the overlying Cretaceous sediments, or (c) was derived from the leaching and erosion of Paleozoic sediments well to the west of the Colorado Plateau. All of these hypotheses are, to some extent, plausible, but are as yet unsubstantiated.”

Well, there you have it.  I purchased the specimen due to the type locality located out in the uranium beds of western Colorado in Montrose County.  Unfortunately, I can’t really tell if it is montroseite or paramontroseite or perhaps it has started to weather into another vanadium minerals.  When one looks at the Bitter Creek specimens on MinDat it seems impossible to separate montroseite from paramontroseite.  However, MinDat only lists a single specimen of montroseite, no paramontroseite, from Burro Mine, and that photographed specimen looks “just like my montroseite.”  I also noted that the MinDat’s photo’s description (written by specimen owner Andrew Hodgson) stated: Old Material, purchased from Ralph Merrill (Minerals Unlimited) in 1983.  Interestingly, the label on my specimen is very fragile and faded (indicating old) and is from Minerals Unlimited with a price tag of $50!  And so I will leave it at that---a learning experience,

REFERENCES CITED

Evans, H. T., Jr . and  Mrose, Mary E., 1955: American Mineralogist, v. 40.

Garrels, R. M. and Pommer, A. M., 1956, Some quantitative aspects of the oxidation and reduction of Colorado Plateau ores:  U.S. Geological Survey Trace Elements Investigations Report 177.

Thamm, J.K., Kovschak, A.A. Jr., and Adams, S.S., 1981, National uranium resource evaluation. Geology and recognition criteria for sandstone uranium deposits of the salt wash type, Colorado Plateau Province. Final report: United States: N. p., 1981. Web. doi:10.2172/6512174.

Weeks, A.D., Cisney, E.A., Sherwood, A.M., 1951, Hummerite and montroseite, two vanadium minerals from Montrose County, Colorado. Abstracts of papers presented at the thirty-first annual meeting of the Mineralogical Society of America at Washington, D.C: American Mineralogist, v. 36.

Weeks, A.D., Cisney, E.A., Sherwood, A.M.,1953, Montroseite, a new vanadium oxide from the Colorado plateaus: American Mineralogist v. 38.