WHY THERE WILL BE NO #MaceralCup

This fall (2017) on Twitter, there have been exciting earth-science voting competitions: the iconic and ground-breaking #MinCup (favorite mineral), the subsequent #RockCup, and the recently-ended (November 2017) #DinoCup. Each competition pitted 32 choices, bracketed by pulling "competitors" out of a hat. #MinCup was the brainchild of @tectonictweets (Dr. Eddie Dempsey, structural geology lecturer at the University of Hull, England); #DinoCup is his paleontological follow-up. Picking up the gauntlet, A-level geology at Greenhead College, Huddersfield, England, held the #RockCup. The goal of these geologic social media/ science communication exercises was both fun geology community interaction and to engage/inform students. As @Geol_Greenhead specifically entreated during #RockCup: "help 16-18yr olds engage with geology[:] tell them about the rocks on their A-level specification". Most participants just voted daily, but many promoted their favorites with photos and relevant information about why their mineral, etc, was better than its competitor that day. #TeamGarnet was a particularly vocal, but ultimately vanquished, group during #MinCup (darn olivine). During #DinoCup, I learned, disappointingly, that the true velociraptor was quite small, possibly with feathers, resembling an ugly turkey; deinonychus was the actual model for the Jurassic Park “velociraptors”. 

Garnet by Hazel Gibson

Dempsey summarized the viral 2017 #MinCup experience in his blog (https://eddiedempsey.wordpress.com/2017/10/15/the-first-mincup/), and #MinCup was touted as a science communication success by various outlets. A beautiful legacy of this year’s #MinCup is Dr. Hazel Gibson’s charity calendar (https://mypatchworkplanet.com/mincup-charity-calendar/https://mypatchworkplanet.com/mincup-charity-calendar/) of mineral-contender ink drawings produced during her contemporaneous participation in #Inktober (“31 days, 31 drawings”).

Following in the success of these initial bracketed earth material/fossil competitions are #FaultCup, #VolcanoCup, and #ExoCup (vote for favorite exoplanet so not actually not “earth” science). There may be others of which I am not aware. A suggested competition is #OreCup. While #MinCup, #RockCup, #DinoCup may be annual events and have multitudinous contenders, is it possible, with further new earth-science-based matches, we could get either burned out or too specialized to have much of an audience?

So as a coal petrologist (although very proud of my earlier amphibolite-grade metamorphic roots [Go #TeamGarnet]), I thought what about a competition for favorite maceral: #MaceralCup? First off, many may query, hopefully politely, what is a maceral? Using an analogy, like the much-maligned ones previously common on US college-entrance exams, maceral:coal::mineral:rock. A maceral, as defined initially in 1935 by paleobotanist and coal petrologist Marie Stopes, is a microscopically distinguishable organic component of coal derived from the decomposed and macerated remains of plants. Besides coal, macerals are found dispersed in sedimentary rocks and are petroleum and natural gas precursors. Maceral names end “inite”. (FYI: Stopes, 1880-1958, is most famous for her books on intimate married relations and birth control, highlighted recently during one episode of Downton Abbey.)

However, there will be no #MaceralCup for the following reasons (Spoiler alert: the most important reason is the culminating #3; #1 is lengthy but informative maceral background for the non-organic geologist):

1) There are only about two-dozen macerals defined for bituminous and anthracite coals (Suárez-Ruiz, 2012; complete citation at bottom). This number of macerals is probably not too few for a competition, but tough to add in new competitors in subsequent years. Maceral quantity increases if one includes the alternate names for vitrinite group macerals that are applied at the lower lignite/brown coal ranks (huminite group). For maceral photomicrographs in white and blue/UV oil-immersion reflected light see https://energy.usgs.gov/Coal/OrganicPetrology/PhotomicrographAtlas/OPTICCoalMaceralClassification.aspx and https://igws.indiana.edu/Coal/Macerals.cfm .

Just FYI, here are macerals with mostly quick definitions. (Definitions below are my own, or derived from Suárez-Ruiz, ICCP citations below, or the linked Indiana Geological Survey photomicrograph pages.):

LIPTINITE GROUP (a flashy competitive group since these lipid-rich components brilliantly fluoresce yellow to red under UV or blue-light excitation; more photomicrographs at https://igws.indiana.edu/Coal/liptinite_include.cfm)

            Sporinite- spores and pollen

            Cutinite- Leaf cuticle, the wax coating of leaves.

            Resinite- Plant resin of various compositions, including the amber of Jurassic Park.

            Alginite- Fossil algae. Can be broken into two subtypes, as described by Hutton (1987): telalginite- from large colonial or unicellular algae; and lamalginite from small thin-walled algae.

            Suberinite- Cell walls of cork

            Chlorophyllinite- Derived from chlorophyll but not present in bituminous and anthracite rank coals (only lignite and subbituminous)

            Fluorinite- This is a subtype of resinite derived from essential oils associated with leaves. Usually found with cutinite, which aids its identification. More intense and yellower epifluorescence than most resinites. This is probably my favorite just because it was always a treat to find it present.

            Bituminite- Fine stringy, filamentous or granular, but essentially unstructured, groundmass from degradation of algae, bacteria or other predominantly autochthonous lacustrine or marine organic matter. Some use “AOM”, amorphous organic matter, interchangeably (me). But, officially the two are not synonymous since a maceral must be a “microscopically recognizable individual constituent” (Pickel et al., 2017), and “AOM” has been used for submicroscopic structureless solid organic matter. “Recognizable” may, however, depend on the magnification (500X-1000X), and discrimination of either bituminite or AOM from a clay matrix in whole rock microscope preparations can be difficult. I personally believe that AOM or bituminite is the same as the fluffy organic component of marine snow. Also bituminite is a confusing name since it can be mixed up by some with the term “solid bitumen” which is a produced hydrocarbon.

            Exudatinite- A secondary crack-filling fluorescing maceral produced during oil generation.

            Liptodetrinite- Liptinite detritus, frequently small, and frequently lacking structural identifiers so source is unknown.

           

Cutinite from Pickel and others (2017)

Darker-orange-fluorescing cutinite (long serrated) enclosing non-fluorescing phyllovitrinite and bright-yellow-fluorescing fluorinite. Yellow "liptodetrinite and sporinite in surrounding matrix". From Pickel and others (2017).

VITRINITE GROUP (The primary, and most abundant, maceral group in most coals, derived from woody tissue of stems, roots and leaves. Vitreous luster. The predictable increase in reflectivity of telinite with increasing diagenesis, “vitrinite reflectance”, is a commonly used very-low-grade-metamorphic indicator. Photos: https://igws.indiana.edu/Coal/vitrinite_include.cfm )

            Telovitrinite subgroup- In this group, the maceral telinite is identified clearly by preservation of woody cellular structure; in collotelinite, texture is more homogeneous with cell walls possibly only barely visible.

            Detrovitrinite subgroup- Vitrodetrinite is small vitrinite detritus. Collodetrinite: gelified vitrinite groundmass binding other macerals (like the gelatin of a fruited Jello (or jelly to you Brits) salad).

            Gelovitrinite- This subgroup is colloidal vitrinitic filling in voids: corpogelinite (discrete bodies between woody plant cell walls); gelinite (gelified vitrinitic fillings of other voids/cracks).

 

Reflected white-light oil-immersion microscopic image showing various macerals.

INERTINITE GROUP (These macerals are generally “inert” in industrial processes like coke-making for the steel industry. All higher reflectance than vitrinite. Many are the products of combustion in ancient widlfires. Photos: https://igws.indiana.edu/Coal/inertinite_include.cfm )

            Fusinite- Classic high-reflectance open-cell (cell walls but empty lumens) charcoal structure.

            Semifusinite- Lower reflectance than fusinite indicating possible lower temperature of combustion. Sometimes fossilized burnt tree trunks or branches show a gradation from fusinite exterior to semifusinite interior.

            Funginite- Highly-reflecting fungal remains.

            Secretinite- Oxidized resin or gel, no plant structures, frequently rounded.

            Macrinite- Structureless, no definite shape, but commonly elongated and high reflectance.

            Micrinite- Tiny, high reflectance, granular maceral. May be residue of AOM or other liptinites after oil generation.

            Inertodetrinite- Small highly-reflecting detritus that cannot be assigned to any of the inertinite groups.

           

2) Personally, some of my favorite macerals are not recognized officially by the ICCP (International Committee for Coal and Organic Petrology, governing body of coal petrographic terminology, www.iccop.org) so would sadly not be contenders. Like #1, this does not preclude a competition but limits competitors:

a) Algodetrinite: This is liptinite detritus derived exclusively from algae. The term was suggested by Adrian Hutton, but he stated that the general official term liptodetrinite should supercede. However, if the goal of a maceral count study is documenting land plant vs. lacustrine/marine organic contribution, the provenance-neutral liptodetrinite is not a useful category if the detritus is clearly algal-derived.

b) Pseudovitrinite- An oxidized, slightly higher reflecting, variety of telinite showing remnant cell structure and tell-tale slits. First described by Benedict and others (1968) of Bethlehem Steel; determining volume percent is a useful predictor of coal behavior in the coking process.

c) Phyllovitrinite- Woody or lignin-cellulose material in leaves. Not listed as an official definition, but a useful descriptor when found enclosed by cutinite.

3) MOST IMPORTANTLY---There will be no #MaceralCup because THERE ARE HARDLY ANY COAL (OR ORGANIC) PETROLOGISTS ON TWITTER!!! I know only a FEW coal-petrology trained geologists on Twitter. One petrologist's research concentration is palynology.  Although I have run into other palynologists on Twitter, not all palynologists (specialists in taxonomic identification of modern and fossil spores and pollen) are trained also in coal/organic petrology and lingo. The other Twitter-savvy organic petrologists, of whom I am aware, specialize in modern and ancient wildfire research, all part of or graduates of the same research group. I searched for names of colleagues and board members in organic petrology professional societies and came up empty. Are there younger organic petrologists I haven’t found? While there would obviously be a spirited debate between #TeamSporinite and #TeamFusinite with the current 7-8 organic petrologists on Twitter, one cannot have an informative, mind-expanding, educational Twitter exchange if no one else is out there.  WHERE ARE YOU ALL??

Citations:

Benedict, L. G., Thompson, R. R., Shigo, J. J. III, Aikman, R. P., 1968, Pseudovitrinite in Appalachian coking coal: Fuel, v. 47, no. 2, p. 125-143.

Hutton, A. C., 1987, Petrographic class of oil shales: International Journal of Coal Geology, v. 8, p. 203- 31.

International Committee on Coal and Organic Petrology, 1998, The new vitrinite classification (ICCP System 1994): Fuel, v. 77, no. 5, p. 349-358.

International Committee on Coal and Organic Petrology, 2001, The new inertinite classification (ICCP System 1994): Fuel, v. 80, no. 4, p. 459-471.

Pickel, W., and others, 2017, Classification of liptinite—ICCP System 1994: International Journal of Coal Geology, v. 169, p. 40-61 (http://ogs.ou.edu/docs/articles/IJCG-V169-P40-61.pdf )

Stopes, Marie, 1935, On the petrology of banded bituminous coals: Fuel in Sci. and Pract., Vol. 14, p. 4-13.

Suárez-Ruiz, Isabel (2012), Organic petrology: An overview, in Al-Juboury, Ali (ed.), Petrology- New perspectives and applications: InTech (http://www.intechopen.com/books/petrology-new-perspectives-and-applications/organic-petrology-an-overview)

Other organic petrology resources see http://carbonacea.blogspot.com/2015/06/coal-and-organic-petrology.html