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”.
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| Garnet by Hazel Gibson |
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 see https://energy.usgs.gov/PhotoAtlas/
.
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.)
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.
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| Cutinite from Pickel and others (2017) |
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| 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. )
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. )
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.
Stopes, Marie, 1935, On the petrology of banded bituminous coals: Fuel in Sci. and Pract., Vol. 14, p. 4-13.
Other organic petrology resources see http://carbonacea.blogspot.com/2015/06/coal-and-organic-petrology.html
