CSMS GEOLOGY POST: 06/17/20

Wednesday, June 17, 2020

FLUORAPATITE, BERTRANITE AND MUHAMMAD ALI

I know little about the geology of Maine and in past excursions was more interested in the fantastic opportunities to sample seafood and explore the home store of L.L. Bean. Early in my career I spent a week camping along the shoreline while pulling a large pop-up camper trailer. Sure, I pounded on the rocks but also spent more time stopping on the roadside so we could gorge ourselves on wild berries and hitting the fishing docks in late afternoon to purchase lobsters and mussels right off the boats. Wow, what a treat. I also took a very early morning hike to the top of Cadillac Mountain on Mt. Desert Island to see the sunrise since that spot receives the first sunshine of the day in the lower 48.

Later, when I was on the undergraduate research speaking circuit, I presented at Bates College, a beautiful private liberal arts college in Lewiston, Maine. A “field trip” one evening took the group over to the L.L. Bean home store in Freeport. In those “olden days” most of us were not living close to a Bean outlet so the home store was just like Christmas.

Lewiston is also well known for a singular event that took place on May 25^th, 1965, when Muhammad Ali knocked out Sonny Liston in the first round of a Heavyweight Championship fight. After the fight, the 23-year-old Ali called the punch that dropped Liston his secret: "It was a phantom punch. It was lightning and thunder — fast as lightning and booming as thunder from the heavens,"

Now that I have more time I am trying to learn, something in detail, about the geology of New England. When I taught Stratigraphy, I told my students that we were lucky to live in the Plains’ states since you could actually see rock outcrops. In New England, the rocks are all covered by vegetation!

The other day I was thumbing through a copy of the Nov/Dec volume of Rocks and Minerals looking for an article containing information on the gem zoisite variety known as tanzanite. After reading about that gem I stumbled on an article entitled The Emmons Pegmatite: Greenwood, Oxford County, Maine. Something popped up in my mind that said, “you have a specimen from there.” So, I took a peek in the drawer and there was a small plastic cube box with a specimen collected by David Shannon in August of 1997 or 1999 (ink smeared).

The Emmons Pegmatite was well described by Falster and others (2019) and I urge readers to examine that issue of Rocks and Minerals where I retrieved the following information.

The Emmons Quarry is found on Uncle Tom Mountain in Oxford County, Maine, and was first mined for feldspar in the 1930s; however, that venture was short-lived. Mineral enthusiasts then started extracting beryl and collected about 5000 carats of gem morganite (pink beryl). Specimen collecting has continued to the present and is especially active with the move of Alexander Falster and William Simmons (and their laboratory) from New Orleans to the Maine Mineral and Gem Museum in Bethel. The Emmons is known for its many phosphate minerals and is Maine’s most species rich pegmatite (109 valid minerals according to MinDat).

The Emmons is part of the New England Appalachian Mountains and the entire New England area has a complex history. I always had a great deal of respect for the geologists deciphering the history of these rocks, especially with the aforementioned vegetation! I have lived through an exciting time in the history of geology where “continental drift, eugeosynclines and miogeosynclines were strange bedfellows in my 1960s era Historical Geology class. Today, 60 years later, the entire concept of plate tectonics has evolved into academic dogma. In my class the text “talked” about Paleozoic mountain building events in the eastern U.S. (todays geography); however, these tectonic pulses, named Taconic (Ordovician), Acadian (Devonian), and Alleghenian (Permian), were distinct events and no one really understood their “cause” or relationship We just studied uplifts and erosion. Today we know that shifting plates were colliding with one another, some were subducted with resulting volcanism and intrusions and metamorphism, and microcontinents were often caught in the middle and were accreted to larger continents. All of this action was continuous during the Paleozoic resulting in the supercontinent termed Pangea. Rocks of the Emmons Pegmatite were originally marine sediments deposited in a deep-water marine basin during the Ordovician-early Devonian and were later subjected to deformation and metamorphism during Devonian to Permian tectonism. For a discussion on the breakup of the supercontinent see Posting October 21, 2019.

My thumbnail specimen that I pulled from the back of the drawer is amazingly rich with albite and other feldspars, manganese dendrites, quartz, several unknowns, bertrandite [Be₄(Si₂O₇)(OH)₂], and fluorapatite [Ca₅(PO₄)₃F]—and probably others. I purchased it for the nice purple crystals of fluorapatite and the gemmy clear bertrandite for which the quarry is famous. At the Emmons Quarry Falster and others (2019) noted that both bertrandite and fluorapatite result from the corrosion and alteration of beryl and form in the vacated cavities/vugs.

Purple fluorapatite (F) and clear gemmy bertrandite (B). Width photo ~7 mm.

Note the tiny, submillimeter, tan prismatic crystals marked with a ?, along with fluorapatite and bertrandite.

I presume the lower arrow points to a number of lilac to clear crystals of fluorapatite (submillimeter). The upper arrow points to a similar situation of stacked crystal of a tan-orange color. Some of the black mineral may be manganese oxide. Lots of questions!