Ferrostrunzite
Mineral Monday
Natura nusquam magis est tota quam in minimis
"Nature is to be found in her entirety nowhere more than in her smallest creatures," or “Nature is never more than the least of all.” Pliny the Elder was talking about living creatures; as you know, I choose to extend his view to minerals. The specimen above is just 18 mm wide.
Strunzite, Mn2+Fe3+2(PO4)2(OH)2 · 6H2O, is an unusual, hydrated manganese-iron phosphate named in 1957 by Harvard mineralogist Clifford Frondel (1907-2002) in honor of German mineralogist Karl Hugo Strunz (1910-2006). This acicular (from Latin for ‘small needle’) mineral was informally called “Frondel’s whiskers” because Frondel was aggressive in seeking enough of it to define the new mineral and name it for Strunz.
Ferrostrunzite is a distinct separate mineral with no manganese, only iron phosphate, Fe2+Fe3+2(PO4)2(OH)2 · 6H2O. My specimen here was labeled strunzite, but strunzite has been discredited at that New Jersey locality, so this is probably ferrostrunzite, whose type locality is Mullica Hill, where mine is from. Even more confusingly, there’s yet another mineral, ferristrunzite, which differs from ferrostrunzite in having only iron in the +3 state versus +2 AND +3 for ferrostrunzite, not to mention that ferrostrunzite has 6 water molecules to ferristrunzite’s five. I knew you wanted to know that little detail.
The field of view in the photo at top is about 4 millimeters, and there’s also a bit of rockbridgeite, yet another iron phosphate (Fe2+Fe3+4(PO4)3(OH)5), the olive green balls near the center of the photo and darker blobs elsewhere. The reddish crusts enclosing the rockbridgeite and separating the cavities containing ferrostrunzite may be some iron oxide, but I think it is likely that they are santabarbaraite, an amorphous, often botryoidal iron phosphate named for a locality in Italy, and which also honors Saint Barbara, patron saint of miners.
Mullica Hill, New Jersey USA, is a classic locality for vivianite (another iron phosphate), from which the ferrostrunzite probably formed by alteration. The site is also well known for abundant invertebrate fossils, including especially belemnites (related to squids) and oysters. Their abundance probably generated the glauconite-bearing greensand and marl of the Navesink Formation (which also contains phosphate nodules) near the end of the Cretaceous Period about 67 million years ago. Glauconite, an iron-magnesium aluminosilicate, is usually taken to be an alteration of excrement from marine organisms.
The abundant life indicated by the fossils and the glauconite might be the source of the phosphorus in the minerals that replace the fossil shells and occur in cavities within them. Glauconite would also easily be the source of the iron to produce the ferrostrunzite and vivianite, and glauconite also may help stabilize the phosphorous derived from organic debris (Xia and others, 2022, Iron rich glauconite sand as an efficient phosphate immobilising agent in river sediments: Science of the Total Environment, 2022 Mar 10;811:152483).
The location was a coastal and near-shore environment, and rare dinosaur bones are also found in the Navesink Formation including hadrosaurs and tyrannosauroids (Brownstein, 2018, Large basal tyrannosauroids from the Maastrichtian and terrestrial vertebrate diversity in the shadow of the K-Pg extinction: The Mosasaur, J. of the Delaware Valley Paleontological Society, v. 10).
The Navesink Formation represents a transition from an inner shelf to outer shelf environment during sea-level rise (Bennington, 2003, Paleontology and sequence stratigraphy of the Upper Cretaceous Navesink Formation, New Jersey: Field Trip, Long Island Geologists). The dinosaurs are found in the lower part, when it was a coastal flat, and the marine animals including belemnites are later, when it was open (but still shallow) sea. Most of what is now southern New Jersey was under water until after the Cretaceous.
According to MinDat, vivianite was named by Abraham Gottlob Werner in 1817 for John Henry Vivian (1785 - 1855), a Welsh-Cornish politician, mine owner, and mineralogist who discoverer of the mineral. The Navesink Formation was named for the community of Navesink, which was named for the indigenous people who lived in east-central New Jersey.
Like the bit of Latin. Had a prof in medieval studies who peppered his lectures with quotes. Having elected to take Latin in high school it was actually a nice touch as far as I was concerned, but darn irritating to most of the class.
I liked this one a lot. The chemistry explanation for strunzite, ferri-, and ferro- versions of the species was particularly good for me. Thanks, Dick!