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sample: FKM-226
locality: Khungtukun Massif, Malaya Romanikha River, Khatanga, Taimyr Peninsula, Taymyrskiy Autonomous Okrug, Eastern Siberian region, Russia.
rock type: Reportedly a hypabyssal intrusion of gabbro through a coal seam, producing an assemblage of highly reduced iron and copper minerals. Some assimilation of ferruginous and argillaceous material from the host rocks during emplacement seems probable given the notably Fe-enriched composition of the mafic silicates and the unexpected presence of K-feldspar and hercynite.
major mineralogy: specimen acquired for native iron, cohenite, plagioclase and pyroxene.

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sample: FKM-227
locality: Eveslogchorr Mtn., Khibiny massif, Kola Peninsula, Russia.
rock type: agpaitic nepheline syenite.
major mineralogy: specimen acquired for astrophyllite.

accompanying videos: Short videos featuring the mineral associations and optical properties of the astrophyllite in this thin section offer a more detailed look at this sample.

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sample: FKM-228
locality: Varenche mine, Saint-Barthélemy, Nus, Aosta Valley, Italy.
rock type: predominately a titanite-albite-quartz-carbonate rock metasomatic rock. The protolith was likely a carbonate-facies Mn-rich chemical (hydrothermal?) sediment that experienced notable As, Sb and V introduction during subsequent metasomatism.
major mineralogy: Quartz, albite (Ab99; with red CL) and Mn-rich calcite make up the bulk of the sample; more silicate- and carbonate-rich areas can be readily distinguished from one another in the scanned image by the gray “cloudiness” of the carbonate-rich zones in unpolarized light. Small patches of kutnohorite occur separately as inclusions within the albite. Hematite blades (and more irregular larger masses of hematite) occur throughout the sample but are most abundant in the carbonate-rich areas. Additionally, several relatively large masses of an Mn-bearing crichtonite mineral also occur in the carbonate-rich zones. The mineral is ostensibly senaite, but is Mn-dominant in the nominally Fe-dominant M2 site. Hence, this Mn-enriched version of senaite is referred to here as “M2Mn-senaite”. Although OH and vacancies are reported in some crichtonite group minerals, this senaite was normalized to 22 total cations and charge-balanced to 38 oxygens; this normalization routine seems to yield good analytical totals and reasonable site occupancies. Large complexly-intergrown and zoned areas of coarse slightly As-enriched titanite and markedly As-enriched apatite (with white CL) occur largely along the boundaries of carbonate- and silicate-rich areas, along with minor talc. The titanite zoning is represented as both larger seemingly homogeneous sector-like areas and as more irregular patchy zones hosted by the main moderate z material. The apatite zoning is more irregular; relatively low-As fluorapatite cores are occasionally rimmed by a thin discontinuous band of As-free fluorapatite (and entire isolated un-zoned crystals of this latter As-free material [with orange CL] are scattered within the rock; this may be the rock’s original apatite prior to As metasomatism?). The low-As fluorapatite cores are not universally present, and indeed more commonly, the dominant composition is a more As-rich material that straddles both sides of the fluorapatite/hydroxylapatite boundary and is irregularly intergrown with a higher-As hydroxylapatite. This latter material not clearly identifiable as a consistent rim or core zone. The notably yellow masses (in hand sample and in the unpolarized light thin section image) are V-bearing manganberzeliite, for which the sample was acquired. This arsenate “garnet” is largely un-zoned, although sparse lower z areas have Mg > Mn and are therefore properly Mn-rich berzeliite. Rare very weakly higher z areas in the manganberzeliite are much higher in Na, much lower in Mg, and also notably differ in Mn and As content. Accounting for a low total (~88 wt%), this material normalizes surprisingly well to Na2Ca3Mn3[AsO4]4(OH)2 . 6H2O; however, this doesn’t correspond to a known mineral and the high proposed H2O content would seem inconsistent with the material’s BSE response (higher average z than manganberzeliite). This material would benefit from further study. The titanite and apatite are both REE-free except for small amounts of Ce; however, small gasparite-(Ce) (with white CL) and REE-bearing chernovite-(Y) occur scattered in the sample. Because the analytical routine used for the unexpected chernovite-(Y) did not include HREE, the estimation of HREE (and the quantification of Gd, which was not optimized for the peak overlaps present in an HREE-abundant mineral) in the two reported chernovite-(Y) compositions should be considered very tentative. An estimation of the HREE based on a chondrite-normalized REE pattern peaking at Gd gave acceptable stoichiometries, charge balances and totals (except in the latter case for the core analysis, where the total was excessively low).

accompanying videos: Short videos featuring the mineral associations and optical properties of the manganberzeliite in this thin section offer a more detailed look at this sample.

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sample: FKM-229 (billet courtesy of J. Worthington, Univ. Arizona; sample 13P121)
locality: Panj River gorge, ~5 km N of Vogde, Tajikistan.
rock type: high grade melanosomic restite in migmatitic leucogranite.
major mineralogy: specimen acquired for garnet.

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sample: FKM-230
locality: Madagascar (a more specific locality is not identified, but the sample resembles material from the Ampanihy rhodonite deposit.
rock type: spessartine-“schefferite”-rhodonite Mn-metasomatite.
major mineralogy: The specimen was a tumbled lapidary material acquired for rhodonite and spessartine. It is dominated by rhodonite, Mn-bearing augite (“schefferite”), and lesser spessartine (particularly concentrated in a band that crosses the sample). The rhodonite contains ~1.7 wt% Mg. If this Mg is preferentially partitioned into rhodonite’s M5-cation site, then Mg would be the dominant M5-cation in this case, akin to Fe in ferrorhodonite (where the Fe is the dominant M5-cation), and the mineral might represent a new end-member of the rhodonite group (see the more-detailed comparable discussion for Zn in Franklin “fowlerite” for sample FKM-54). Undifferentiated Mn-oxides are abundant particularly as extremely fine stringers in the augite, although scattered larger crystals, identified as takanelite, are also present in both the augite and the rhodonite. Small inclusions of rhodochrosite are similarly present in both the augite and rhodonite, and these appear to vary slightly in Ca and Mn content, depending on the nature of the host mineral. In one augite, rare small inclusions of Mn-bearing titanite and Mn-bearing tremolite were observed. Normalization of the small Mn-bearing tremolite results in a formula that appears to be slightly deficient in ∑M-site cations (VIM+VIIIM = 6.91; see below). Although certainly perhaps the result of a poor analysis due to the grain’s small size, another possibility is the presence of unanalyzed ∑M cations. A fairly common unanalyzed element in amphiboles is Li, and the addition of only a very small amount of Li (~750 ppm) would actually be sufficient to fill the deficiency (and such a minor amount would also not adversely alter the total). The amphibole in this thin section is likely too small to test this possibility with LA-ICP-MS (once our Element2 is up and running) or SIMS, but in the future additional amphibole will be sought in the preserved billet to test this.

accompanying videos: Short videos featuring the mineral associations and optical properties of the Mn-bearing augite and rhodonite in this thin section offer a more detailed look at this sample.

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sample: FKM-231
locality: Mendes Pimentel, Minas Gerais, Brazil.
rock type: test.
major mineralogy: specimen acquired for brazilianite.

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sample: FKM-232
locality: stated by the dealer as “southern India”; however, the material has been alternatively reported as being from northeastern India (reportedly from the Ganjam area, Orissa state).
rock type: test.
major mineralogy: specimen acquired for corundum and cordierite.

accompanying videos: Short videos featuring the mineral associations and optical properties of the sillimanite in this thin section offer a more detailed look at this sample.

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sample: FKM-233
locality: stated by the dealer as “southern India”. This material is widely available online as tumbled stones (notably among the “healing crystal” community), but frustratingly, no one seems to have a more specific locality than just “India”. This material is too popular and too distinctive to remain a mystery; I will eventually figure this one out!
rock type: almandine-biotite-plagioclase schist.
major mineralogy: specimen acquired for spinel (however from the scanned images, the isotropic mineral appears to be garnet… update: it is garnet). Abundant porphyroblasts of weakly-zoned almandine-pyrope garnet in a matrix of “black” biotite, plagioclase and quartz. Scattered fluorapatite, minor rutile and sparse allanite-(Ce) are also present.

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sample: FKM-234
locality: Russia (the material was purchased as a polished cabochon from a “gem” dealer, so a more specific locality was not provided. However, the sample resembles the “Orlets”-type material from the famous rhodonite mines of the Yekaterinburg area, Middle Urals).
rock type: test.
major mineralogy: specimen acquired for “Orlets”-type rhodonite. However, with the continued study and recent expansion of the rhodonite group, the dominant rhodonite group composition here does not appear to be rhodonite, but presumably is instead the newly-named (in 2019) vittinkiite, where M5Mn2+ > M5Ca; however, subordinate portions of the weakly zoned crystals do fall just on the rhodonite side of the nomenclature boundary. The rhodonite deposits of the Yekaterinburg area are one of the few regions currently listed for vittinkiite, although presumably more localities will be identified as older rhodonite analyses are re-evaluated. Minor black (in hand sample) Mn oxide (oxyhydroxide?) is scattered in the vittinkiite, but it is not entirely clear what its identity is (or how many minerals may be represented by this material). The material is very fine-grained and was difficult to analyze. Some is fairly definitively braunite (although with a bit low total); a single analysis of Si-free material is consistent (although with a bit low total) with Mn4+O2, for which pyrolusite is the most abundant and widespread polymorph and so a likely possibility. However, other Mn4+O2 polymorphs (akhtenskite, ramsdellite) can not be precluded, nor can nsutite (a presumably less widespread mixed Mn4+-Mn2+ oxyhydroxide that has nonetheless been identified in the Urals “Orlets”-type rhodonite deposits). Even manganite or groutite can not be analytically excluded. For now the material is tentatively assigned as pyrolusite, pending further characterization.

accompanying videos: Short videos featuring the mineral associations and optical properties of the rhodonite group mineral vittinkiite in this thin section offer a more detailed look at this sample.

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sample: FKM-235
locality: Summit Rock, Klamath Co., Oregon, USA.
rock type: reported as an andesite in the mineral collector literature, the rocks seems to be a bit more mafic and Fe-rich than a typical calc-alkaline andesite and seems somewhat closer to a basaltic ferro-andesite (the Fe-enrichment in the mafic silicates seems reminiscent of a tholeiitic differentiation trend[?]; the “basaltic” adjective is based in part on the SiO2 content of the dominant plagioclase that makes up the majority of the rock… thus whole rock SiO2 seems likely to end up under 56 wt%).
major mineralogy: The specimen was acquired for fayalite (in lithophysae), but the olivine present in the rock occurs primarily in the groundmass and is less Fe-rich than fayalite and is “hyalosiderite” (Fo60); indeed, the dominant larger cavity crystals purported to be fayalite are actually “hypersthene” (orthopyroxene). The groundmass is largely plagioclase zoned from “bytownite” cores through to “andesine” outer rims. Also present are several pyroxenes, including “hypersthene” and some smaller groundmass augite possibly intergrown with pigeonite. Although pigeonite is reported by Kleck, 1970 as a common groundmass mineral in the Summit Rock lavas, all of the groundmass pyroxene crystals in this sample exhibited very fine-scale exsolution lamellae. While care was taken to locate cleaner areas to analyze, potential overlap between opx and fine-scale hidden cpx lamellae mistaken as small pigeonite grains cannot be precluded. Also widespread are abundant Fe-Ti-oxides. These include large magnetite partially oxidized to hematite, and somewhat smaller ilmenite partially altered to thin bands of TiO2 (rutile?; likely poor analysis). Fluorapatite and zircon occur as an additional accessory minerals.

accompanying videos: Short videos featuring the mineral associations and optical properties of the enstatite in this thin section offer a more detailed look at this sample.

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sample: FKM-236
locality: Jakobsberg Mine, Jakobsberg ore field, Nordmark district, Filipstad, Värmland, Sweden.
rock type: Although not associated with a causative intrusion, and indeed presumably formed by a completely different process, this mineralization style has been commonly referred to as a “Mn skarn”. A better term for this and related occurrences may be “calcareous Mn-metasomatite”. The original Fe and Mn were likely derived from exhalative hydrothermal processes, perhaps akin to those of modern seafloor “black smokers”. While enrichments of some of the associated elements such as As, Sb, Ba and Pb may have been contemporaneous, others such as Be and B were likely introduced later. Subsequent high-grade metamorphism (perhaps accompanied by additional metasomatism) facilitated the redistribution of elements into the diverse and unusual mineral assemblages we observe today.
major mineralogy: The specimen was acquired for barylite and hausmannite. Hausmannite is abundant in the sample; however, no barylite was observed in this thin section, nor is the mineral reported from the Jakobsberg mine (although that does not necessarily preclude its occurrence there, as it does occur in the geologically-similar main Långban area nearby). There appear to be at least two, and possibly four generations of calcite in this sample. In one portion of the thin section, relict phantoms of sharply sector-zoned calcite (the BSE contrast seems to be controlled by Pb) is engulfed in additional Pb-free calcite. This “flood” calcite is compositionally similar to the “main low-z” calcite otherwise abundant elsewhere in the sample, although this latter material also shows local patchy zoning, apparently also a function of Pb content. Small scattered patches of rhodochrosite accompany the main calcite; small grains of barytocalcite, some as inclusions in hausmannite, round out the carbonates present. The dominant silicates include tephroite with subordinate richterite and alleghanyite (some of the latter altering along the edges to braunite). Minor Mn-rich phlogopite is also present. A survey for additional high-z phases uncovered sparse barite, scattered kentrolite, and one small grain of långbanite. The långbanite grain appeared to be zoned, although the higher z portion (with 4.7 wt% Pb) yielded a low total (~95 wt%) and would not normalize well (with the Si-site overfilled by ~0.3 apfu and the M2+-site correspondingly underfilled by ~0.3 apfu). Subtraction of all the Pb and equal moles of Si (i.e. suggesting admixture most simply ascribed to alamosite [reported at the locality]) corrected the normalization and resulted in a formula comparable to the low-z portion; however, only the higher-quality low-z långbanite analysis is reported here. Several patches of a brownish sheet(?) silicate are present. This mineral can be normalized to a serpentine-like formula (with only Si in the T-sites), but this results in an M-site filling reminiscent of chlorite, with M-site vacancies and significant M3+. The analytical total with the inclusion of 8[OH] apfu (approriate for either serpentine or chlorite) would be excellent at 100.3 wt%. In all these respects, the formula resembles an Mn-Mg-greenalite. That such a normalization does not resemble any recognized species, however, is troubling. Alternatively, this analysis can be normalized to a pyrosmalite-like formula. Both T-site occupancy (Si+Al = 5.97 apfu) and M-site occupancy (Mn2++Fe2++Mg = 8.02 apfu) appear excellent. However, complicating this assessment is that additional larger cations such as Pb, Ca and Na add another 0.11 apfu (maybe contained in the ring voids?), Cl is essentially absent, the overall total is only 97.2 wt% (although comparable to the confirmed pyrosmalite in sample FKM-190), and lastly, that the expected upper 2nd order birefringence is not observed here (obscured by the deeper mineral body color?). As with the “serpentine” normalization, the result of the “pyrosmalite” normalization also struggles to resemble previous literature-reported analyses. This material would certainly benefit from additional study.

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sample: FKM-237
locality: Magnet Cove, Hot Spring Co., Arkansas, USA.
rock type: reported as a nepheline syenite, although no nepheline is present in the sample and instead analcime is the silica-undersaturated alkali silicate present. However, the accompanying alkali feldspar has been significantly sericitized, so the current analcime may represent an alteration product of former nepheline. If the analcime is primary rather than secondary, the rock would be an analcime syenite.
major mineralogy: specimen acquired for aegirine.

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sample: FKM-238
locality: Pacific Limestone Products Quarry (Kalkar Quarry), Santa Cruz, Santa Cruz Co., California, USA.
rock type: Ba-metasomatized marble.
major mineralogy: The specimen was acquired for gersdorffite and molybdenite, but of the two, only gersdorffite was observed during a cursory BSE examination; however, the prevalence of other high z phases (typically Ba-rich minerals) may have obscured small amounts of molybdenite, and X-ray mapping for Mo may be warranted to locate it, if present. The rock is largely composed of sub-equal dolomite and finely-pitted calcite (the latter yielding consistently slightly-low analytical totals of ~94 to ~97 wt%, perhaps due to the open space). Abundant forsterite and subordinate diopside (bright blue CL) and tremolite are present, appear relict from the prograde metamorphic path (and likely prior to metasomatism), and are now partially replaced by an undifferentiated serpentine that appears admixed with small amounts of an additional indistinguishable S-bearing (sulfide?, sulfate?) phase. Kinoshitalite is widespread and may be the dominant silicate present (hence odd that it hasn’t been previously reported from this well-studied locality); the grains are made up of notably rounded Ba-enriched cores and slightly more K-bearing overgrowths. A curious Ba-Mg-Al chloro-silicate occurs as sparse thin overgrowths on kinoshitalite or as occasional small isolated grains within the host carbonate. Several almost-identical analyses of this mineral normalize surprisingly well to the general Ba4VIM4[O]2(OH)4[Si4O12][Si2O3(OH)4]Cl2 formula that Kampf et al., 2013 [← subscription required] propose for the cherchiaraite group, but with some necessary adjustments. The unknown differs in several critical aspects to the three currently recognized chechiaraite group members: an extra ~0.50 apfu Ba is present; the four VIM cations are 2+ (Mg) rather than the nominal 3+ (Al, Fe3+ or Mn3+); only ~0.50 apfu Cl is present; and perhaps most interestingly, two of the nominal six apfu Si appear to be replaced by Al. The net charge difference resulting from the cation replacements is -5; +2 of this imbalance can be accommodated by protonating the two non-tetrahedral oxygens associated with the Mg. An additional +2 can be accommodated by protonating the last two non-bridging oxygen atoms in the Al-dimer (so in fact the overall dimer charge remains unchanged). The remaining +1 can be accommodated by maintaining a partial vacancy in the Cl-site and only adding sufficient [OH] necessary to charge balance the formula. The H2O mass of the this fully protonated proposed formula brings the analytical total up to ~95 wt%, which may not be unreasonable for a small grain of a very hydrous potentially beam-sensitive mineral. If this mineral is indeed “cherchiaraite-like”, it is unclear where the 0.5 apfu cation excess in the Ba-site would be structurally accommodated, and for book-keeping purposes it’s simply tacked on to the end of the formula here (although note that the large Cl channel-fill site is still partially vacant). In any case, it is reasonably certain that the mineral contains the Si4O128- ring common to both the cherchiaraite and taramellite groups (minerals of the latter group being present at this locality) given the essentially integer normalization values for Al, Mg and Ba. But given the possibility that other elements could be present (i.e. B, as in taramellite) and that the proposed extensive protonation to charge balance the formula may not be realistic or even structurally viable, the identity of this unknown remains mysterious and worth further study. Abundant apatite near the fluorapatite-hydroxylapatite boundary; minor barite and sphalerite; and rare zircon, galena and pyrrhotite are also present. Sample FKM-220 is from the same locality, but contains Ba-feldspar + pabstite rather than Ba-mica, more abundant silicates overall, and also a different and much richer sulfide assemblage.

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sample: FKM-239
locality: Raidlgraben, Fritzbach valley, Pöham, Werfen, Salzburg, Austria.
rock type: test.
major mineralogy: specimen acquired for lazulite.

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sample: FKM-240 (two thin sections cut from the same billet are shown here)
locality: Obsidian Cliffs, North Sister Mountain, McKenzie Pass, Lane Co., Oregon, USA.
rock type: test.
major mineralogy: specimen acquired for osumilite. The osumilite occurs as vapor-phase growth deep blue crystals in lithophysae abundantly scattered in the hand sample, and sparsely intersected in an exploratory epoxy mount.

accompanying videos: Short videos featuring the mineral associations and optical properties of the osumilite in this thin section offer a more detailed look at this sample.

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sample: FKM-241
locality: Lågendalen, Hedrum, Larvik, Vestfold, Norway.
rock type: test.
major mineralogy: specimen acquired for catapleiite.

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sample: FKM-242
locality: Nordmark region, Filipstad, Värmland, Sweden (suggested by the dealer to be from the Kitteln ‘2’ mine, although a locality in the Kitteln area with a “2” suffix is not noted in the extensive mindat.org database).
rock type: test.
major mineralogy: specimen acquired for orthopinakiolite, although morphologically, chemically and by associations, the borate present more closely resembles the Fe-rich fredrikssonite described in Enholm, 2016.

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sample: FKM-243
locality: Bald Knob deposit, Bald Knob, Sparta, Alleghany Co., North Carolina, USA.
rock type: kutnohorite-galaxite-alleghanyite Mn-metasomatite. This rock was originally a carbonate-dominated bulk composition Mn-rich chemical sediment (hydrothermal exhalite?) subsequently metamorphosed to mid-upper amphibolite facies P-T conditions (575±40 °C; 5±1 kbars; Winter et al., 1981).
major mineralogy: specimen acquired for kellyite, galaxite and kutnohorite.

accompanying videos: Short videos featuring the mineral associations and optical properties of the alleghanyite and kellyite in this thin section offer a more detailed look at this sample.

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sample: FKM-244
locality: Gem mine, San Benito River headwaters area, New Idria district, San Benito Co., California, USA.
rock type: test.
major mineralogy: specimen acquired for benitoite, neptunite and natrolite.
accompanying videos: Short videos featuring the mineral associations and optical properties of the benitoite and neptunite in this thin section offer a more detailed look at this sample.

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sample: FKM-245 (billet from the Univ. Arizona petrology collection, sample Wards 22)
locality: Salem Neck, Essex Co., Massachusetts, USA.
rock type: nepheline syenite.
major mineralogy: specimen acquired for nepheline and biotite.

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sample: FKM-246
locality: Rapid Creek, Dawson Mining District, Yukon, Canada.
rock type: metasomatized sedimentary phosphorite.
major mineralogy: specimen acquired for lazulite, wardite and augelite.

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sample: FKM-247
locality: Iodake, Satsuma-Ioujima, Mishima village, Kagoshima Prefecture, Nansei Archipelago, Kyushu region, Japan.
rock type: test.
major mineralogy: specimen acquired for roedderite.

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sample: FKM-248 (billet from the Univ. Arizona petrology collection, sample Wards 45)
locality: Portland Point, Tompkins Co., New York, USA.
rock type: mica peridotite.
major mineralogy: specimen acquired for phlogopite and garnet.

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sample: FKM-249 (billet from the Univ. Arizona petrology collection, sample Wards 23)
locality: near Red Hill, Moultonborough, Carroll Co., New Hampshire, USA.
rock type: This Wards sample is identified as a nepheline sodalite syenite, but no sodalite is apparent in hand sample or in thin section. However, a small amount of cancrinite is present, so this sample might be more appropriately identified as a cancrinite nepheline syenite.
major mineralogy: The rock is predominately meso-microperthitic orthoclase and some nepheline, with subordinate cancrinite. The mafic mineral assemblage consists of intergrown clusters of aegirine-augite, an Fe-rich NaCa-amphibole generally on the ferro-ferri-katophorite side of the composition boundary with ferro-ferri-taramite, and an Fe-rich biotite (annite). Scattered magnetite and very tiny (hence difficult to analyze well) ilmenite is present. Minor aeschynite-(Y) intergrown with zircon contains 2.13 wt% Yb as part of the HREE complement, as well as 1.1 wt% Th, 2200 ppm U and 2100 ppm Pb. Sparse monazite-(Ce), small areas of an alteration Ca-bearing REE-fluorocarbonate poorly-defined but somewhat consistent with röntgenite-(Ce), and a small weakly-zoned possible pyrochlore-group mineral round out the REE mineralogy. Zoned fluorapatite is scattered in the sample and also occurs as inclusions in the mafic minerals.
accompanying videos: Short videos featuring the mineral associations and optical properties of the aegirine-augite and ferro-ferri-katophorite in this thin section offer a more detailed look at this sample.

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sample: FKM-250 (billet from the Univ. Arizona petrology collection, sample Wards 46)
locality: Murfreesboro, Pike Co., Arkansas, USA.
rock type: mica augite peridotite.
major mineralogy: specimen acquired for phlogopite, augite and olivine.

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