KANSAS PSEUDOMORPHS: LIMONITE AFTER PYRITE

A couple of years ago, while attending the RMFMS meeting in Wichita, Kansas, a gentleman walked in with a paper bag and approached a dealer where I was examining a few specimens.  He opened the bag and asked the dealer if he could help identify his rocks.  Being curious, I stayed around to look at “what was in the bag.”  To my surprise, he dumped several nice mineral octahedrons on the case and said he found them along a “draw” over in Marion County.  Well, this really piqued my interest since mineral crystals are not all that common in Kansas—except for the Tri-State Lead and Zinc District in the southeast part of the state.  My initial guess, without handling the specimens, was weathered magnetite.  I hustled away to locate a magnet and a loupe from a friend but alas, when I returned, the sack was “gone” and the dealer said the specimens were purchased by “someone.”  So that tale ended there on the Kansas prairie.

A generic octahedron mineral belonging to the Isometric System.  Crystals in this System have three axes of equal length meeting at 90 degrees, labeled below as axes X+ X-, Y+ Y-, and  Z+ Z-.  Diagrams courtesy of metafysical.nl.

Upon returning home I could not find evidence of larger specimens of magnetite that had been found in Kansas.  A few small octahedrons are present in the kimberlites north of Manhattan and the “black sands” found in western Kansas streams usually contain tiny magnetite grains (detected by a magnet).  That was about it until I ran across a reference to a small article published by A.C. Carpenter in the 1941 Transactions of the Kansas Academy of Science, New Mineral Localities in Kansas: 

Although small octahedrons of limonite pseudomorphs after magnetite or pyrite have been found in Kansas for at least 50 years [late 1880s], definite localities where they found be located remained unknown.  All known collections either bore the label “from Kansas” or else carried the name of a county as McPherson, Dickinson, and Marion. Last New Year’s week I…found a number of octahedrons of limonite pseudomorphs on the John Reimer farm in sec. 12, T. 18 S., R. 4 E., 1 mile north and 1 ¼ miles east of Lincolnville in Marion County…A second locality is reported to be near Roxbury in McPherson County.  

 
 A glance of the Kansas Geological Survey’s selection of county geologic maps indicates that Marion County does not have a county report nor county map.  Therefore, the larger scale State Map was used to place the collecting locality in Permian strata, probably rocks of the Sumner Group (redbeds and evaporite).  In addition, Carpenter noted that additional limonite pseudomorphs were reported (no reference) “to be near Roxbury.”  That small town is in northeastern McPherson County, east of Marion County, where a small sliver of Sumner Group rocks, maybe the lower formation (Wellington) crop out along a creek.  That is my best guess; however, I cannot locate references describing pyrite (or limonite) in these rocks.

Mindat.org believes that limonite is probably not a recognized mineral name but is used for unidentified massive hydroxides and oxides of iron, with no visible crystals and a yellow-brown streak.  Limonite is most commonly the mineral goethite (FeO(OH).  Chemically, limonite is Fe,O,OH,H₂O or Fe,O(OH)-nH₂O.  Pyrite is FeS₂and limonite forms during chemical weathering where water hydrates the iron but the original crystal shape of pyrite remains..

One of my former students, living in Kansas, knew I was interested in these Kansas crystals and sent me ₂copy of a brochure published by a New York mineral dealer in 1902.  One of the minerals offered for sale by George L. English was LIMONITE PSEUDOMORPHS AFTER MAGNETITE, Kansas.  Excellent ¼ to 3/8 inch octahedrons, 1 dozen for 10c.  Evidently the 1902 brochure came from a 2017 discussion on MinDat (https://www.mindat.org/mesg-7-409374.html) where a consensus was reached that the crystals were limonite after pyrite rather than after magnetite.

Advertising brochure from George L. English.

However, there is more to the story.  The first tidbit is that I recently was rummaging around a rock shop and behold there was a stray octahedron with a label stating, “limonite after magnetite, Kansas.”  It had to be! Yep, it looked just like the newly determined limonite after pyrite crystals pictured on MinDat.  So now, I finally had one of these somewhat elusive Kansas crystals.

Octahedron of limonite pseudomorph after pyrite. Axes are ~1.2 cm.

The second tidbit involves the New York dealer, George L. English. According to the Mineralogical Record Biographical Archive, English was a very famous collector and dealer (certainly more so that I knew). He was born in Philadelphia (1864) and was selling minerals in that city by 1887: “a truly wonderful assortment of Arizona wulfenites, vanadinites, azurites, and malachites in addition to fine Franklin fowlerites.”  He picked up a couple of partners and opened a New York branch 1887 and by 1889 his ad stated, “We deal exclusively in minerals…It is universally acknowledged that we have the finest and most complete stock of minerals in the United States.”  In 1896 English incorporated his company, now completely in New York, and sold 150 shares (at $100 each).  Mr. Lazard Cahn was a member of the Board of Directors. English spent the latter part of his life working for, and with, Ward’s Natural Science Establishment, serving as a consulting mineralogist, evaluating collections and establishing monetary values for minerals, and writing a very popular book entitled Getting Acquainted with Minerals.  He recognized as new minerals penfieldite, graftonite, pyroxmangite, and skemmatite, and referred them to investigators for detailed descriptions. A rare hydrous phosphate of calcium, potassium, and aluminum from near Fairfield, Utah, was named englishite in his honor.  English died in 1944.

Mineral labels, early 1900s, of New York mineral dealers George L. English and Lazard Cahn.  Both from the Mineralogical Record label collection.

Of interest to me, other than the limonite after pyrite octahedrons, was English’s relationship to the founder, and Honorary President for Life, of my home club, the Colorado Springs Mineralogical Society.

Wilson, in the Mineralogical Record Biographical Achieves, noted Cahn began dealing in mineral specimens for pleasure in the mid-1890's from his offices in New York City. Cahn's first advertisement appeared in the Exchange Column of the July 1895 issue of The Mineral Collector. He wanted to buy or exchange for "very choice, well crystallized American minerals," and offered for sale Colorado amazonite and orthoclase twins, rhodochrosite crystals on matrix, bastnasite pseudomorphs, arfvedsonite crystals and pyrite crystal groups. So, by 1896 Lazard Cahn evidently was a well-respected mineral collector/dealer living in Colorado Springs while keeping an office in New York and was invited to join the Board of Directors of the George L. English Company.

I've always loved life, and I've never known what's ahead. I love not knowing what might be round the corner. I love serendipity.  (Twiggy).  So it goes, round and round: Octahedron pseudomorphs---George English---Lazard Cahn---Colorado Springs Mineralogical Society---Mike---Octahedron pseudomorphs!!

HYDROXYLHERDERITE: ANSWERING ONE OF LIFE'S PERSISTENT QUESTIONS

I picked up a mineral in Tucson last year because: 1) it was a phosphate (one of my favorite groups); 2) I knew very little about locality or abundance, well actually nothing; 3) it was sort of a bland looking, did not have really well developed crystal faces and was like an orphan on a table of more spectacular and showy specimens; and 4) it was cheap in price.  So, off I went with my small specimen of herderite, rescued from its disgrace at the showy ball.  Herderite [CaBePO₄(F,OH)] is a calcium beryllium phosphate and is usually found in granite pegmatites rich in beryllium (for example beryl).  It was discovered many decades ago in Germany (Haidinger, 1828) and so I now had a little jewel that was no longer an orphan.  But wait, something is wrong!

According to the people-in-the-know, I almost certainly have a specimen of hydroxylherderite, also a calcium beryllium phosphate [CaBePO₄(OH,F)]. There is a subtle difference between the two minerals—note the end of the chemical formulae.  In hydroxylherderite the hydroxyl radical (OH) is greater than the fluorine component (F).  The opposite is true in herderite.  Could I tell the difference?  Probably not. Gatta and others (2014), in studying the herderite-hydroxylherderite in Oxford County, Maine, used the following instruments: single-crystal X-ray diffraction and neutron Laue diffraction, electron microprobe analysis in wavelength-dispersive mode, inductively coupled plasma-atomic emission spectrometry and polarized Raman spectroscopy.  Let’s see, my lab has a microscope or two, a loupe, a hardness kit, and a bottle of acid---no inductively coupled plasma-atomic emission spectrophotometer though (maybe for Christmas?).

Hydroxylherderite was given the name hydrohererite when it was described from localities around Paris, Maine (Penfield, 1894).  I am a little uncertain about how Penfield was able to distinguish his specimens as different from the original herderite—one of life’s persistent questions (see addendum).

Both minerals are quite similar in their physical properties with a hardness of around 5.0-5.5 (Mohs), poor cleavage, white, colorless, blue green, blue, purple/lavender (only hydroxylherderite), brown, light yellow (in color), translucent to transparent with a luster ranging from vitreous to waxy/greasy.  The streak is white.  Both belong to the Monoclinic Crystal System and crystals often are prismatic.

The "orphan,"  a hydroxylherderite prismatic crystal on lepidolite (a lithium-rich mica).  The lack of a "pink" color of the lepidolite evidently is due to a lack of manganese.  Length of exposed crystal is ~1.2 cm.

As one might suspect there is a solid solution series between herderite and hydroxylherderite; however, no mineral with an intermediate composition is named.  And again, one needs some rather sophisticated instrumentation to distinguish chemical composition.  MinDat notes that most specimens labeled herderite are actually hydroxylherderite and confirmed F-dominant specimens are presently known only from Brazil (two locations), Mogok (Burma), Yichun (China), and Namibia.  Evidently, even the type locality specimens (Germany) of herderite are now confirmed as hydroxylherderite.  The only way that I might be able to distinguish specimens is that the lavender/purple crystals from Brazil are hydroxylherderite.  In fact, my specimen is from the Virgem da Lapa, Minas Gerais, Brazil (Xanda Mine?), and shows some purple/lavender color. Hydroxylherderite from this area is composed of 53-64% (OH) as the end member (Dunn and others, 1979).

Another partial crystal of hydroxylherderite on the same specimen displaying the purple/lavender color common in Brazilian specimens.  Width of photomicrograph ~2.5 cm.

Both minerals are late-stage members of granite pegmatite hydrothermal mineralization (Dunn and others, 1979) and seem to be formed from the alteration of beryllonite [NaBePO₄] (Palache and Shannon, 1928), or beryl [Be₂Al₂(Si₆O₁₈)] (Yatsevich, 1935).  I thought perhaps hydroxylherderite might be widely present in the beryllium-rich pegmatites of the Black Hills, South Dakota; however, MinDat only lists a single locality, the famous Tiptop Mine near Custer.

REFERENCES CITED

Dunn, P.J., C.W. Wolfe, P.B. Leavens, and W.E. Wilson, 1979, Hydroxyl-herderite from Brazil and a guide to species nomenclature for the herderite/hydroxyl-herderite series: Mineralogical. Record, v. 10.

Gatta, G.D., S.D. Jacobsen, P. Vignloa, G.J. McIntyre, G. Guastella, L.F. Abate, 2014, Single-crystal neutron diffraction and Raman spectroscopic study of hydroxylherderite, CaBePO4(OH,F): Mineralogical Magazine, v. 78, no. 3.

Haidinger, W., 1828, On herderite, a new mineral species: Philosophical Magazine, 4, 1-3.

Palache, C. and E.V. Shannon, 1928) Beryllonite and other phosphates from Newry, Maine: American Mineralogist v. 13, 392-396.

Penfield, S. L., 1894, On the crystallization of herderite: American Journal of Science, 3rd Series, 47, 329-339.

Yatsevich, G. M., 1935, The crystallography of herderite from Topsham, Maine: American Mineralogist, v. 20, 426--437.

ADDENDIUM I

Above I stated that I was uncertain about how Penfield knew the Maine mineral this was not herderite and indeed was a new mineral.  I finally located an 1894 copy of the American Journal of Science (wow, James and Edward Dana, editors) and Penfield fully explained: DURING the past summer Mr. L. K. Stone of Paris, Maine, sent to Prof. H. L. Wells of the Sheffield Scientific School several specimens of an unknown mineral for identification. The specimens were collected at Paris, Me., but not at the noted Mt. Mica locality. They presented well defined, transparent and almost colorless monoclinic crystals, measuring up to 2mm in diameter and 6mm in length. The crystals are implanted mostly upon quartz hut some are on feldspar. Their hardness is a little over 5. When tested before the blowpipe they at first sprouted and turned white, but afterwards fused at about 4 to a white, blebby enamel, tinging the flame very pale green, indicating phosphoric acid. In the closed tube at a high temperature the crystals whitened, threw off quite violently a fine scaly powder or dust and gave water which showed only a faint acid reaction. The mineral was slowly but completely soluble in hydrochloric acid. As these characters apparently did not agree with the description of any known species, the mineral was supposed to be new and accordingly the best material available for the chemical analysis was carefully selected and eventually separated from any attached quartz or gangue by means of the heavy eolution. The pure mineral, amounting to about one and a half grams, and varying in specific gravity from 2'936 to 2'968, was analyzed by Professor Wells to whom the author's sincere thanks are due. The analysis revealed the interesting fact that the mineral is herderite and that it contains practically no fluorine, agreeing in this latter respect with a variety described by Professor Wells and the author* from Hebron, Me….The analyses indicate a well defined type of herderite which may well be called hydro-herderite in distinction from the variety containing fluorine.

Now, that is real science!  But I am still uncertain about Professor Wells and his analysis indicating “no fluorine.”  How was that fact determined?  A chemist friend of mine explained that in 1894 elemental fluorine had only been isolated by Henri Moissan 8 years earlier in 1886.  Although Moissan received the Nobel Prize in Chemistry for his work, he had studied results of other chemists who had been trying to isolate the element for about 75 years.  Some of these boys (all were males) had ended up as "fluorine martyrs" while working with highly corrosive hydrofluoric acid (HF).

So, the identification of fluorine in early chemical analyses is one of life’s persistent questions that I will continue to explore.  The beautiful thing about learning is nobody can take it away from you  (B.B. King).

ADDEEDUM II 

R.I.P.  JOHN McCAIN 

I prefer to give thanks for those blessings, and my love to the people who blessed me with theirs.  The bells toll for me.  I knew it would.  So I tried , as best I could, to stay a part of the main.  I hope those who mourn my passing, and even those who don't, will celebrate as I celebrate a happy life lived in imperfect service to a country made of ideals, whose continued service is the hope of the world.  And I wish all of you great adventures, good company, and lives as lucky of mine.