samples FKM-251 to FKM-275


Check out the thin section scans introduction page for more information on the variety of samples featured here, how the scans were taken & processed for web display, and what additional optical and analytical data I hope to include in the figure captions as I continue to update the site and add to the collection of thin sections.

There’s also a fully searchable index covering the complete thin section set, listing for each sample its locality, the anticipated major minerals, a brief generalized geologic environment description, and where appropriate, the nature of any unusual element enrichments.

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sample: FKM-251 (billet from the Univ. Arizona petrology collection, sample Wards 32)
locality: Mont Saint-Gregoire (Mont Johnson; Monoir), Le Haut-Richelieu RCM, Montérégie, Québec, Canada.
rock type: essexite (nepheline monzodiorite).
major mineralogy: Plagioclase > orthoclase. Nepheline is interstitial to the feldspars and is abundantly flecked with tiny fibers (too small to quantitatively analyze) of what appears to be a Ca-dominant zeolite where Al:Si ≈ 1:1 (hence akin to a phase such as gismondine); interstitial patches of analcime are also present. The dominant mafic silicate present is ferri-kaersutite, intergrown with lesser amounts of a Ti+Fe3+-rich biotite and still lesser amounts of a sub-silicic Ti-rich clinopyroxene near the augite-diopside nomenclature boundary. The pyroxene and amphibole show essential no grain boundaries under BSE imaging (so the minor pyroxene is actually easier to spot under the petrographic microscope than under BSE), with the amphibole typically overgrowing the pyroxene, and in places a boundary of amphibole separates pyroxene from biotite. Within the larger clots of mafic minerals are also abundant large fluorapatite, magnetite (with a significant ülvospinel component; some magnetite crystals contain lamellae and coarser clots of ilmenite) and mildly-zoned titanite (with up to ~1.9 wt% Zr). Scattered zoned small zirconolite and rare baddeleyite round out the Zr-bearing assemblage. Scattered small pyrrhotite and rare pyrite are also observed.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-251
pyrrhotite Fe0.87S1.00
pyrite Fe1.00S2.00
ilmenite (Fe2+0.76Mg0.13Mn2+0.06Fe3+0.05)(Ti0.95Fe3+0.04V0.01)O3
(most Mn2+-rich)
(most Ti+Fe2+-rich)
magnetite (most Fe3+-rich;
adjacent to ilmenite)
(most Th+U-rich core)
zirconolite (middle) (Ca0.85Ce0.03Th0.02La0.01Nd0.01Y0.01[HREE]~0.01U0.01)(Zr0.95Ti0.04Hf~0.01)
(most Ca+Zr-rich rim)
fluorapatite (Ca4.93Sr0.02Na0.02Ce0.01FeT0.01)[P2.96Si0.03S0.01O12](F0.78[OH]0.20Cl0.01)
titanite (most Al+Fe-rich) Ca0.99(Ti0.89Fe3+0.04Al0.03Zr0.02V0.01)(O0.89[OH]0.06F0.05)[Si0.97Al0.03O4]
titanite (most Zr-rich) Ca0.99(Ti0.88Zr0.04Fe3+0.03Al0.02V0.01Nb0.01)(O0.92[OH]0.05F0.03)[Si0.97Al0.03O4]
augite (Ca0.88Na0.06Mg0.05Mn2+0.01)(Mg0.72Fe2+0.11Fe3+0.11Ti0.04Al0.01)[Si1.84Al0.16O5.99F0.01]
(most Mg-rich; main)
(most Fe-rich; rim)
“biotite” (K0.88Na0.06Ba0.010.05)(FeT1.26Mg1.10Ti0.36MnT0.030.25)[Si2.61Al1.28Fe3+0.11O10]([OH]1.16O0.72F0.11)
orthoclase (most K-rich) (K0.65Na0.30Ca0.03Sr0.01)[Si2.93Al1.07Fe3+0.01O8]
orthoclase (most Na-rich) (K0.58Na0.39Ca0.03Sr0.01)[Si2.92Al1.08Fe3+0.01O8]
“andesine” plag ss
(most Ca-rich cores)
“oligoclase” plag ss
(most Na-rich rims)
nepheline (Na2.60K0.54Ca0.14Sr0.010.71)[Si4.15Al3.82Fe3+0.03O16]
analcime (Na0.960.04)[Si1.97Al1.03O6] . H2O


sample: FKM-252
locality: reportedly from “Kiev, Ukraine”. However, this locality is not entirely consistent with the sample’s purported combination of minerals; here an overview of the geology of Ukraine is instructive. Devonian and Permian evaporites in Ukraine form a belt in the east of the country, and Jurassic and Miocene evaporites form a sub-parallel belt in the west of the country, as well as a smaller exposure in the south near Kerch, Crimea (Hryniv et al., 2007) [← subscription required]. In contrast, running up through the center of the country (including in the vicinity of Kiev) is the 3.0 Ga Golovanevsk suture zone, which hosts a number of mafic-ultramafic bodies that also include chromatites (Gornostayev et al., 2004) [← subscription required]. So this being a chromite-bearing sample from the Kiev vicinity is certainly plausible. However, the possibility of boracite in this samples seems extremely unlikely.
rock type: apparently a chromatite clot in dunite.
major mineralogy: This specimen was labeled as “boracite with chromite”, and although the association of a chloro-borate typical of a sedimentary evaporite with a Cr-bearing spinel typical of an ultramafic igneous rock seems suspect, I was intrigued enough to purchase the sample (thinking, for example, that an ultramafic body could have intruded an evaporite). Although the billet is currently still out for thin section preparation, I prepared a small epoxy mount of the material to examine in advance. EPMA of this epoxy mount verifies abundant magnesiochromite and forsterite, with small amounts of Cr-enriched diopside. There is a widespread very low z Mg-silicate phase veining the olivine that seems inconsistent with either expected talc or serpentine (with an analytical total only 72 wt% and molar Mg:Si ≈ 11:4), so there is still some intrigue associated with this sample that will have to wait for resolution until the thin section comes back.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-252
magnesiochromite (Mg0.66Fe2+0.33Mn2+0.01)(Cr1.51Al0.42Fe3+0.05Fe2+0.01)O4
forsterite Mg1.00(Mg0.90Fe2+0.08Ni0.01)[Si1.00O4]
diopside (Ca0.98Na0.01Mg0.01)(Mg0.94Fe2+0.02Cr0.02Al0.01Fe3+0.01)[Si1.97Al0.03O6]
low z Mg silicate? analysis pending


sample: FKM-253
locality: Darai-Pioz glacier, Alai range, Tien Shan Mtns., Tajikistan.
rock type: highly-evolved B-rich alkali granite.
major mineralogy: specimen acquired for stillwellite-(Ce).
(left: unpolarized light; right: under crossed polars)



sample: FKM-254 (dealer sample number 1048)
locality: Solongo boron deposit, Buryatia, Transbaikalia region, Eastern Siberia, Russia.
rock type: calcic borate skarn.
major mineralogy: specimen acquired for frolovite.
(left: unpolarized light; right: under crossed polars)



sample: FKM-255 (dealer sample number 4372)
locality: Nežilovo, Veles, Macedonia.
rock type: metasomatized(?) marble.
major mineralogy: specimen acquired for zincohögbomite-2N6S.
(left: unpolarized light; right: under crossed polars)



sample: FKM-256 (dealer sample number 3433)
locality: Arroyo de la Yedra, ~6 km NNE of Manzanares el Real, Eastern Pedriza Massif, Sierra de Guadarrama, near Madrid, Spain.
rock type: “episyenite”; desilicified and alkali-metasomatized granitoid.
major mineralogy: specimen acquired for ferri-whittakerite. However, B(NaLi) amphiboles such as “ferri-whittakerite” have been reclassified into either B(NaNa) or B(LiLi) groups. Hence, this material is now presumably either ferri-leakeite [B(NaNa)] or ferri-pedrizite [B(LiLi)], depending on whether the B-site is predominantly Na or Li. Note that there is reportedly significant compositional variation among the Pedriza Massif amphiboles and so even zoned single crystals may span these and related species. Because of this variability, in-situ micro-analysis for Li by either SIMS or LA-ICP-MS is necessary to properly characterize individual BSE-recognizable growth zones.
(left: unpolarized light; right: under crossed polars)



sample: FKM-257 (dealer sample number 3002)
locality: Srednyaya Padma mine, Velikaya Guba uranium-vanadium deposit, Zaonezhie peninsula, Lake Onega, Karelia Republic, Russia.
rock type: add rock type.
major mineralogy: specimen acquired for chromceladonite.
(left: unpolarized light; right: under crossed polars)



sample: FKM-258 (dealer sample number 4280)
locality: Case Parigi, Martiniana Po, Piedmont, Italy.
rock type: whiteschist.
major mineralogy: specimen acquired for ellenbergerite. This sample is from the same general vicinity as FKM-42, but differs somewhat in mineralogy.
(left: unpolarized light; right: under crossed polars)



sample: FKM-259 (dealer sample number 6887)
locality: Illutalik Island, Narsaq, Kujalleq, Greenland.
rock type: aegirine, albite and narsarsukite-bearing peralkaline trachyte dyke.
major mineralogy: specimen acquired for emeleusite.
(left: unpolarized light; right: under crossed polars)



sample: FKM-260 (dealer sample number 3429)
locality: Hørtekollen, Sylling, Lier, Buskerud, Norway.
rock type: magnetite-helvite skarn.
major mineralogy: specimen acquired for helvite and fluorite.
(left: unpolarized light; right: under crossed polars)


sample: K-65 (covered and yellowing thin section from Univ. Arizona petrology collection [unfortunately, the original billet & hand sample appear to be lost], Krantz collection, sample K-65)
locality: Kaltes Tal, Bad Harzburg, Harz Mtn. region, Niedersachsen, Germany.
rock type: mica peridotite (as small lenses in norite). Also known locally as “glimmerite”.
major mineralogy: Based on petrography, predominately forsterite and red Ti-rich(?) biotite, with gray spinel and minor oxide (believed to be ilmenite).
(left: unpolarized light; right: under crossed polars)


previous page (samples FKM-226 to FKM-250)

This “add photo(s)” image is just a placeholder in advance of adding new samples, so check back periodically to see my progress.