samples FKM-326 to FKM-350

 

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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left image: unpolarized light; right image: under crossed polarizers; use slider in center to view more of either image

under shortwave ultraviolet [SWUV] illumination

 
sample: FKM-326 (dealer sample number 7010)
locality: Kuh-i-Lal, Pyandzh River Valley, Gorno-Badakhshan, Tajikistan.
rock type: high grade magnesian marble.
major mineralogy: The specimen was acquired for clinohumite and spinel.

 



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under shortwave ultraviolet [SWUV] illumination

 
sample: FKM-327 (dealer sample number 4290)
locality: Area Novo-Dzhaginskoe deposit, Omsukchan, Ducat District, Kolyma River Basin, Magadan Oblast, Russia. Little appears written in English about the locality, although it is mentioned in passing as a “tin-silver” deposit in the introduction of an Ore Geology Reviews article on the nearby Rogovik deposit (Zhuravkova et al., 2017); that single mention references an article entitled “Geology of silver-complex-metal mineralization of the Novyi Dzhagyn intrusive arched structure” by Kalinin et al., 1984 in the journal Kolyma (in Russian). According to a no longer accessible .kml file, the coordinates for the locality appear to be 62°47’46.1″N 155°25’21.5″E. In an additional compilation reference, Nokleberg et al., 2005 (p. 386; Table 4) lists “Novy Djagyn” as a porphyry Sn deposit at 62°48’N 155°25’E. Similar but less detailed data are also compiled earlier in Nokleberg et al., 1997 (p. 26; deposit # P56-14).
rock type: possibly a metamorphosed B-bearing advanced argillic alteration assemblage associated with a Sn(+Ag) deposit.
major mineralogy: The specimen was acquired for dumortierite.

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

mineral PPL (lower
polar rotation)
PPL
(stage rotation)
XP
(stage rotation)
optic figure
(stage rotation)
dumortierite
PPL: pinkish-red/near colorless pleochroism, high relief;
XP: up to 1st order red-purple δ;
with tourmaline, quartz and muscovite

 



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sample: FKM-328
locality: Trikorfo area, Theologos, Thasos, East Macedonia and Thrace, Greece.
rock type: plagioclase-viridine-quartz lenses in manganiferous metapelitic gneiss. A recent description of the geology of the locality is given by Voudouris et al., 2016, which also includes mineral composition data complementary to what is (or will be) given here.
major mineralogy: The specimen was acquired for manganian andalusite (“viridine”).

mineral representative mineral compositions in FKM-328
hematite (Fe3+1.94Al0.02Ti0.02Mn3+0.01Mg0.01Mn2+0.01)O3
rutile (Ti0.98Fe3+0.01)O2
fluorapatite (Ca4.88Mn2+0.06Fe3+0.02Na0.01)[P0.993Si0.003As0.003O4]3F1.00
monazite-(Ce) (Ce0.41La0.20Nd0.18Pr0.05Sm0.03Gd0.03[HREE]0.03Y0.03Th0.03Ca0.02)[P0.95As0.03Si0.01O4]
andalusite (“viridine”) (Al0.88Mn3+0.06Fe3+0.05Mg0.01)Al1.00O1.00[Si0.99Al0.01O4]
sillimanite (Al0.97Fe3+0.02)Al1.00O1.00[Si1.00O4]
phlogopite (K0.85Na0.05Ba0.010.09)(Mg2.42Al0.35FeT0.08Mn2+0.05Ti0.020.08)[Si2.88Al1.12O10]([OH]1.65F0.31O0.04)
clinochlore (Mg4.41Al1.33MnT0.09FeT0.07Zn0.010.09)[Si2.78Al1.22O10]([OH]7.89F0.10)
quartz not analyzed
“oligoclase” (Na0.72Ca0.25)[Si2.75Al1.25O8]

accompanying videos: Short videos featuring the mineral associations and optical properties of the Mn-bearing andalusite (“viridine”) in this thin section offer a more detailed look at this sample.

mineral PPL (lower
polar rotation)
PPL
(stage rotation)
XP
(stage rotation)
optic figure
(stage rotation)
andalusite (“viridine”)
PPL: greenish-yellow/green/bright yellow pleochroism, high relief;
XP: up to 1st order gray δ, partially masked by body color of mineral and by strong anomalous blue/brown overtones;
with quartz, plagioclase and mica

 



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sample: FKM-329
locality: Prabornaz mine, Saint-Marcel, Val d’Aosta, Italy.
rock type: test. Blueschist to eclogite facies meta-Mn-rich sediment (distal volcanogenic exhalite?) at peak conditions retrograded to greenschist facies, with superimposed accompanying metasomatism (Tumiati et al., 2010).
major mineralogy: The specimen was acquired for purple manganian omphacite (violane).

accompanying videos: Short videos featuring the mineral associations and optical properties of the omphacite (“violan”) in this thin section offer a more detailed look at this sample.

mineral PPL (lower
polar rotation)
PPL
(stage rotation)
XP
(stage rotation)
optic figure
(stage rotation)
omphacite (“violan”)
PPL: very weak lavender pleochroism, high relief;
XP: up to 2nd order green δ;
with calcite and very minor piemontite

 



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sample: FKM-330
locality: Mt. Cavalluccio, Sacrofano Caldera, Campagnano, Rome, Lazio, Italy.
rock type: Pyroclastic flow-related ejectum of feldspathoid-bearing alkali-syenite composition.
major mineralogy: The specimen was acquired for mottanaite-(Ce).

 



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sample: FKM-331
locality: Cerchiara Mine, Borghetto Vara, Vara Valley, La Spezia Province, Liguria, Italy.
rock type: Although the overall mineralogy of the larger assemblage from which this small hand sample was obtained is uncertain, this particular specimen is essentially a namansilite-dominant Mn metasomatite.
major mineralogy: The specimen was acquired for namansilite, and in hand sample appears to be composed largely of the deep-red massive pyroxene. Small scattered vugs show delicate fiber bundles of namansilite growing into now calcite+[minor quartz]-filled former open space. Under BSE, the massive namansilite is heavily included with abundant tiny braunite, and is also variably veined with a variety of fine-grained hydrous retrograde or alteration products, including variable-composition Mn-rich amphiboles, noelbensonite, orientite, a possible “manganipyrophyllite” admixed with quartz, and a possible Ba-analogue of bostwickite. Some fine-grained K-feldspar is also present. Overall, except for the pyroxene, calcite, and quartz, all of the other minerals were extremely fine-grained, possibly multi-phase, and were difficult to analyze accurately due to almost certain unavoidable beam overlap with adjacent phases. Hence, the purported “manganipyrophyllite” and the “Ba-dominant bostwickite” in particular should be considered tentative until samples with sufficient size crystals more amenable to analysis can be evaluated. In addition to these “hypothetical” phases, the fine-grained nature of the amphiboles as well made their analyses and normalizations challenging. Two of the amphibole analyses (one represented by pt. #69), both with the highest Ca contents, gave somewhat low overall totals and also appeared somewhat Si-deficient; normalization to ∑(all cations) = 16 appeared to be the best way to approach relatively full IVT-site occupancy (7.95-7.96 apfu) without having to resort to adding imaginary B or Be or assuming there could be unrecognized IVT-site vacancies. The other potential IVT-site cations P, S, and As were all sought but not found to be present. An outcome of this normalization is that essentially all Mn ends up assigned as Mn2+. Three additional amphibole analyses (two represented by pts. #71 & #79), these with lower Ca contents, gave ostensibly better totals, but also appeared to have high Si contents and to require most to all Mn assigned as Mn3+. Despite an apparently real overall bulk chemistry difference with the previous amphibole, these significant differences between the two amphibole populations nonetheless seemed unexpected. In an attempt to account for the difference, small amounts of Si (assumed due to admixed quartz) were subtracted from the latter analyses, sufficient to yield 8.00 apfu Si using the same ∑(all cations) = 16 normalization scheme. This reduced the Mn3+/∑Mn ratio to values under 0.5 (closer, but not identical, to the earlier analyses), and also produced A-site Na and K contents comparable to the earlier analyses. This also resulted in a lone “mangani-winchite” re-normalizing to a more conventional manganoan richterite, which is also more comparable to the other analyses. Still, needless to say, resorting to ad-hoc corrections to these amphibole analyses based on assumptions about admixed contaminating phases is not an ideal solution to the characterization of these minerals. These analyses, along with those of the other fine-grained phases, should be re-evaluated in a more suitable sample or with techniques capable of better spatial resolution.

mineral representative mineral compositions in FKM-331
calcite (Ca0.99Mn2+0.01)[CO3]
braunite (Mn2+0.77Ca0.18Mg0.03)(Mn3+5.95Al0.05)O8[Si0.98Al0.01P0.01O4]
noelbensonite
(very tiny grains)
(Ba0.63Sr0.20Ca0.11K0.02Na0.01)(Mn3+1.22?Mn4+0.58?Al0.03Mg0.010.16)[Si2.00O7](OH)2.00 . H2O
namansilite (Na0.98Ca0.01Mn2+0.01)(Mn3+0.96Mn2+0.02Mg0.02)[Si2.00O6]
orientite
(most [Ca+Mg]-rich)
(Ca6.78Mn2+0.45Mg0.37Sr0.10Na0.07Ba0.03K0.010.19)(Mn3+9.83Al0.13Cr0.01Ti0.01Zn0.01)
[Si0.997P0.003O4]3[Si3.00O10]3([OH]9.99Cl0.01) . 4H2O
orientite
(most [Ba+Mn]-rich)
(Ca6.69Mn2+0.61Na0.18Sr0.15Ba0.13Mg0.07K0.010.16)(Mn3+9.96Al0.03Ti0.01)
[Si0.997P0.003O4]3[Si3.00O10]3([OH]9.98F0.02) . 4H2O
richterite
(most Na-rich; pt. #79)
(Na0.72K0.27)(Na1.44Ca0.56)(Na0.02Mg3.89Mn2+0.60Mn3+0.42Ni0.03Fe3+0.01Al0.01Co0.01Zn0.01)
[Si8.00O22]([OH]1.87F0.13)
richterite
(most Mg-rich; pt. #71)
(Na0.65K0.34)(Na1.10Ca0.55Mn2+0.35)(Mg4.18Mn2+0.68Ni0.05Fe3+0.03Al0.03Mn3+0.02Co0.01Zn0.01)
[Si8.00O22]([OH]1.90F0.10)
richterite
(most Mn-rich; pt. #69)
(Na0.73K0.30Sr0.01)(Ca1.04Na0.85Mn2+0.11)(Mg3.17Mn2+1.76Ni0.04Co0.01Zn0.01)
[Si7.93Al0.02Fe3+0.02O22]([OH]1.91F0.08)
“manganipyrophyllite”?
(fine-grained, with quartz)
(Na0.02Ca0.02)(Mn3+1.86Mn2+0.17Mg0.010.96)[Si4.00O10](OH)2.00
K-feldspar (K0.98Ca0.01MnT0.01)[Si3.01Al0.99O8]
quartz not analyzed
“Ba-bostwickite”?
(very tiny grains)
(Ba0.62Na0.28Ca0.13)(Mn3+5.92Mg0.05)(Si2.84Al0.15)O16 . 5(?)H2O

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

mineral PPL (lower
polar rotation)
PPL
(stage rotation)
XP
(stage rotation)
optic figure
(stage rotation)
namansilite
PPL: orange-yellow/deep red/magenta pleochroism, high relief;
XP: birefringence color masked by body color of mineral;
with calcite and minor quartz
presumably B(-)
but no useful optic figure was found

 



left image: unpolarized light; right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-332 (billet courtesy of V. King [Rochester, NY])
locality: Lewistown area, Fergus Co., Montana, USA.
rock type: The rock appears to be a low to moderate temperature sodic-calcic alteration assemblage facilitated by alkali chloride metasomatism; gypsum mining in the area indicates associated evaporites and a potential source for hypersaline brines. The purported V-enriched epidote group mineralization (mukhinite) itself is in or near [so presumably related to] highly-vanadiferous oil shale in the central Montana Mississippian age Heath Formation (reported locally up to ~8000 ppm V2O5; Desborough et al., 1981).
major mineralogy: The specimen was acquired for mukhinite. Although mukhinite is reported from the locality, it was not observed in this sample. Instead, a Cr-bearing allanite-(Ce) exhibiting only a modest V-enrichment is the notable epidote-group mineral present in this sample, although it does show a pleochroism scheme similar to that reported for mukhinite. This allanite shows an extreme LREE enrichment, particularly rich in La and Ce, but even already much reduced by Pr, Nd and beyond to the MREE and HREE. This REE enrichment pattern is similar to that observed from allanite and other REE-bearing minerals attributed to growth during alkali chloride metasomatism (for example, REE-enriched titanite from certain Fe-oxide-Cu-Au [IOCG] systems: Mazdab et al., 2008); the accompanying unusually high Cr content and additional modest V would then have presumably been sourced from the regional rocks through which the fluids have circulated (although Cr is not listed among the metals [V, Ni, Mo, Se, Zn] specifically reportedly as enriched in the Heath Formation oil shale [Desborough et al., 1981]). Additional evidence for the involvement of alkali chloride brines is the presence of Cl-rich scapolite in the sample. The Cr-enriched allanite-(Ce) crystals are variably zoned. The particular crystals highlighted in the accompanying video consist of more strongly-colored cores, of patchy but variably-high REE and Cr contents (and ranging from Cr-bearing allanite-(Ce) [cf. points #30 & #32] to boundary compositions that appear to just cross into the REE-bearing “tawmawite” field [cf. point #33]), rimmed by a sharply-defined less strongly-colored rim of variably-zoned lower REE+Cr content clinozoisite (cf. points #51 & #52; the latter analysis of a particularly low-z patch shows a notable 1030 ppm Ga enrichment). However, elsewhere in the sample this discrete rim is absent, and the “core” allanite-(Ce) crystals instead show a weak gradational enrichment towards a somewhat higher REE+Cr content (e.g. specifically point #30). Additional fairly coarse clinozoisite is present in the matrix. This matrix material is REE-free and Cr-free and contains only a minor amount of V (~500 ppm); the relationship of this matrix clinozoisite to either the “core” allanite-(Ce) or the “rim” [REE+Cr]-bearing clinozoisite is not clear, as they are not necessarily in contact. In addition to the scapolite, both albite and K-feldspar are present, as is abundant quartz (both as essentially small monominerallic veinlets and within the bulk matrix). Weakly-zoned tremolite with minor variable [Cr+V] enrichment is abundant in the sample; in some cases it is intergrown with the K-feldspar. Accessory zircon and sparse titanite, pyrrhotite and chalcopyrite are also present. There also appears to be a poorly defined very-low-z infilling phase that doesn’t appear readily amenable to analysis; EDS of this material suggests some Fe, S, Cl and Si may be present, although it may be dominated by carbonaceous material.
 
*Note: Microprobe analysis of a Cr±V-bearing allanite is especially challenging due not only to the expected X-ray peak overlaps of the REE, but also due to the added interferences of Cr and V in the same X-ray wavelength region. A consequence of this was that the nominal background positions for the Cr and V measurements were obscured by the shoulders of REE peaks (primarily those of La and Ce), resulting in over-estimation of the background and thus decreased nominal concentrations of Cr and V. This was manifested as somewhat low analytical totals and high Si apfu values. Ideally, the best way to mitigate this is to make careful wavelength scans and then if possible to identify “clean” background positions. However for this preliminary work, and recognizing the issue, each Cr and V concentration was simply increased by a percentage of the point’s combined La+Ce concentrations. To further simplify the calculation, the percentages applied to Cr and V were identical, and were selected to optimize the overall analytical totals and the Si apfu values. The correct ranged from an addition of 2%-4% of La+Ce.

mineral representative mineral compositions in FKM-332
pyrrhotite Fe0.90S1.00
chalcopyrite Cu0.99Fe1.01S2.00
zircon not analyzed
titanite Ca1.03(Ti0.86Al0.10Fe3+0.01)(O0.83[OH]0.13F0.04)[Si1.00O4]
allanite-(Ce)-dominant epidote-group ss
(most REE-rich; patchy outer core)
point #30
(Ca0.95Fe2+0.04Mn2+0.01)(Ce0.39La0.29Ca0.25Nd0.04Pr0.03Th0.01)(Al0.94Cr0.05Ti0.01)Al1.00
(Fe2+0.60Mg0.16Cr0.13V0.09Fe3+0.02)(O0.99F0.01)[Si2.00O7][Si0.99Al0.01O4](OH)
allanite-(Ce)/”tawmawite” boundary
composition epidote-group ss
(most Ca-rich; patchy inner core)
point #32
(Ca0.94Fe2+0.05Mn2+0.01)(Ca0.47Ce0.25La0.20Nd0.04Pr0.02Th0.01Sr0.01)(Al0.94Cr0.05Ti0.01)Al1.00
(Fe2+0.46Cr0.26V0.11Fe3+0.09Mg0.08)O1.00[Si2.00O7][Si0.99Al0.01O4](OH)
“tawmawite”/allanite-(Ce) boundary
composition epidote-group ss
(most Cr-rich; patchy inner core)
point #33
(Ca0.96Fe2+0.03Mn2+0.01)(Ca0.53Ce0.21La0.17Nd0.04Pr0.02)(Al0.97Cr0.03Ti0.01)Al1.00
(Fe2+0.43Cr0.36V0.10Mg0.06Fe3+0.05)(O0.99F0.01)[Si2.00O7][Si1.01O4](OH)
clinozoisite (main patchy in discrete
overgrowth rims; most Cr-rich)
point #51
(Ca0.96Fe2+0.02Mn2+0.01)(Ca0.55Ce0.22La0.18Nd0.03Pr0.01Th0.01)Al1.00Al1.00
(Al0.26Fe2+0.22Mg0.22Cr0.18V0.12)O1.00[Si2.00O7][Si1.00O4](OH)
clinozoisite (patchy in discrete
overgrowth rims; most Al-rich)
point #52
Ca1.00(Ca0.78Ce0.10La0.07Nd0.02Pr0.01Y0.01Sr0.01)(Al0.97Ga0.01)Al0.99
(Al0.65Fe2+0.16Cr0.11Mg0.03V0.03Mn2+0.01)O1.00[Si2.02O7][Si1.01O4](OH)
clinozoisite (large unzoned in matrix) (Ca0.98Fe2+0.01Mn2+0.01)(Ca0.97Sr0.02)Al1.00Al1.00
(Al0.75Fe3+0.17Fe2+0.06V0.01)O1.00[Si2.02O7][Si1.00O4](OH)
tremolite (core; most Fe-rich) (K0.040.96)(Ca1.92Na0.08)(Mg4.29Fe2+0.46Al0.18Cr0.02V0.02Mn2+0.01)
[Si7.81Al0.19O22]([OH]1.77F0.22O0.01)
tremolite (rim; most Mg-rich) (K0.010.99)(Ca1.94Na0.02Fe2+0.02Mn2+0.01)(Mg4.69Fe2+0.14Al0.08Cr0.06V0.03)
[Si7.96Al0.04O22]([OH]1.76F0.24)
tremolite (patchy; most [Cr+V]-rich) (K0.020.98)(Ca1.93Na0.05Mn2+0.01)(Mg4.49Fe2+0.18Al0.17Cr0.11V0.04)
[Si7.80Al0.20O22]([OH]1.85F0.14O0.01)
quartz not analyzed
K-feldspar (K0.95Na0.04Ba0.01)[Si3.00Al1.00O8]
albite (Na0.92Ca0.08)[Si2.92Al1.08O8]
marialite (Na1.83Ca0.99K0.17Sr0.01)[Si7.99Al4.01O24] . (Ca0.51Na0.390.10)(Cl0.49[CO3]0.46)

accompanying videos: Short videos featuring the mineral associations and optical properties of the Cr-bearing allanite-(Ce) in this thin section offer a more detailed look at this sample.

mineral PPL (lower
polar rotation)
PPL
(stage rotation)
XP
(stage rotation)
optic figure
(stage rotation)
[Cr+V]-bearing allanite-(Ce)
PPL: very pale green/moderate reddish-brown pleochroism,
high relief;
XP: up to 2nd order blue-green δ;
with tremolite, quartz and feldspars

 



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sample: FKM-333
locality: Aghbar Mine, Bou Azzer District, Ouarzazate Province, Drâa-Tafilalet, Morocco.
rock type: test.
major mineralogy: The specimen was acquired for roselite.

 



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sample: FKM-334
locality: N’Chwaning II Mine, Kuruman, Kalahari manganese field, Northern Cape, South Africa.
rock type: “Cu-Mn-vesuvianite”-hausmannite metasomatite. The protolith may have been a facies of a subaqueous Mn-rich exhalite, but it has been subsequently metamorphosed and presumably metasomatized.
major mineralogy: The specimen was acquired for manganvesuvianite and hausmannite. In hand sample, the “manganvesuvianite” crystals are a deep red color, but in thin section, the crystals are markedly optically zoned in shades of orange through purple (the crystals are additionally pleochroic). The “blue” component of the purple zones is due to a notable minor Cu substitution, and indeed EPMA indicates sufficient Cu in many portions of the crystals to normalize to cyprine. Zones of lower Cu content normalize to manganvesuvianite (*but see note below). The dominant mineral in the thin section is opaque hausmannite, which hosts the cyprine/manganvesuvianite in open-space filling; within the hausmannite are small streaky compositional zones that show as weakly brighter in BSE; these areas are somewhat enriched in Pb. Also within the hausmannite are inclusions of Sr-rich fluorapatite, minor braunite, and a few larger crystals of Sr-free barite. Also present is henmiterierite, which occurs both as small scattered inclusions within the “Cu-Mn-vesuvianite” and as separate aggregates of small crystals.
 
*Note: Vesuvianite normalization can be challenging because of a combination of factors not readily discoverable by EPMA alone. These complicating factors include an unknown redox state of the Fe and/or Mn present, the possibility of partial dehydrogenation of the hydroxyl, the possibility of vacancies in a number of sites, and the possibility of unanalyzed light elements (particularly B and Be) or unanalyzed elements not routinely sought in silicates (e.g. Sb, Bi). To attempt to accommodate some of these challenges, the analyses have been normalized to a variable “true” cation content between 50 and 55; any value above 50 represent a combination of both any measured or estimated B in the T1 or T2, as well as an estimate of small “over-abundances” of Si and/or Al. As B-bearing minerals are present at N’Chwaning II, the possibility of B was mathematically tested, but was discounted as significant due to the negative effect on the overall charge balance resulting from adding any B. The “true” cation content was then iteratively adjusted until [X1+X2+X3+X4] = 19, [Y1+Y2+Y3] = 13 (if necessary, this allows small excesses of Al to shunt into the normally vacant T2 site), and the Si sites = 18 (if necessary, this allows small excesses of Si to shunt into the normally vacant T2 site). This normalization scheme shunts a small amount of Mn2+ into the Ca sites, and precludes any vacancies in either the Ca sites or Si sites (for example, from the exchange [□4H+]1[Si4+]-1). The cation distributions presented below are estimated from literature expectations and are unfortunately not based on any sample-specific structural work. All Cu2+ has been assigned to the square-pyramidal Y1 site. In all but one analysis, Y1Cu2+ exceeds 0.5 apfu (indeed, up to ~0.9 apfu), and so most analysis unequivocally normalize to cyprine. More problematic is that in lieu of concrete structural data, there are multiple possibilities of which cation should be selected to fill the remainder of the Y1 site, and in at least one case this decision can have a significant effect on the species determination. Structural refinement work by Armbruster et al., 2002 on cuprian manganvesuvianite specifically from N’Chwaning II fill the Y1 site with Mn3+; unfortunately, the Cu2+ of their samples are relatively low, and they omit Cu from their refinement altogether. In contrast, a comparable effort on the cation distributions in cyprine from the nearby Wessels mine, done by Panikorovskii et al., 2017 [← subscription required], shows Mg as the cation accompanying Cu in Y1. For the present work, Mn3+ was selected as the accompanying cation, in part to maintain consistency from sample to sample, but also because in the most Cu-rich sample, there is insufficient Mg to fill the site; hence, some Mn3+ would have been necessary anyway. As alluded to earlier, an outcome of this assignment is that in the one composition showing less than 0.5 apfu Cu2+, the balance of 0.55 apfu Mn3+ results in a normalization to manganvesuvianite; had Mg been used instead, the composition would normalize to magnesiovesuvianite. As this latter species is not reported from any of the Kalahari manganese field mines, the choice of Mn3+ is further supported. Finally, where there wasn’t originally enough Mn3+ to fill the Y1 site, a final conversion of some OH to O increases Mn3+ at the expense of Mn2+.

mineral representative mineral compositions in FKM-334
hausmannite
(main)
(Mn2+0.99Mg0.01)(Mn3+1.98Fe3+0.02)O4
hausmannite
(streaky higher z)
(Mn2+0.96Fe3+0.020.02?)(Mn3+1.97Pb4+?0.03)O4
barite (Ba0.99Sr0.01)[S1.00O4]
hydroxylapatite (Ca4.60Sr0.26MnT0.02)[P0.997As0.003O4]3([OH]0.79F0.21)
henritermierite (Ca2.96Mn2+0.04)(Mn3+1.24Fe3+0.46Al0.29Mg0.01)[Si0.7470.253O2.988(OH)1.012]3
braunite (Mn2+0.87Ca0.08Mn3+0.05Na0.01)Mn3+6.01O8[Si0.97Al0.01O4]
manganvesuvianite-dominant
vesuvianite group ss
(pt. #55)
(Ca18.61Mn2+0.36Sr0.02)(Mn3+0.55Cu2+0.45)Al4.00(Al5.36Mg2.20Fe3+0.34Mn3+0.08)
T1(□3.72Si0.28)T2(□1.00)[Si2.00O7]4[Si1.00O4]10O1.00([OH]8.18O0.47?F0.35)
cyprine-dominant
vesuvianite group ss
(most Mg-rich; pt. #64)
(Ca18.78Mn2+0.21Sr0.01)(Cu2+0.69Mn3+0.31)Al4.00(Mg2.96Al2.95Mn3+1.22Fe3+0.79V3+0.07)
T1(□3.50Al0.37Si0.13)T2(□1.00)[Si2.00O7]4[Si1.00O4]10O1.00([OH]8.41F0.59)
cyprine-dominant
vesuvianite group ss
(most Al-rich; pt. #56)
(Ca18.59Mn2+0.38Na0.02Sr0.01)(Cu2+0.72Mn3+0.28)Al4.00(Al6.33Mg1.32Fe3+0.26Mn2+0.05Ni0.03)
T1(□3.88Si0.12)T2(□1.00)[Si2.00O7]4[Si1.00O4]10O1.00([OH]8.28O0.37?F0.35)
cyprine-dominant
vesuvianite group ss
(most Fe-rich; pt. #65)
(Ca18.73Mn2+0.24Sr0.02)(Cu2+0.75Mn3+0.25)Al4.00(Al4.47Mn2+1.71Fe3+0.82Mg0.52Mn3+0.47)
T1(□3.75Si0.25)T2(□1.00)[Si2.00O7]4[Si1.00O4]10O1.00([OH]8.37F0.62)
cyprine-dominant
vesuvianite group ss
(most Cu-rich; pt. #54)
(Ca18.56Mn2+0.33Na0.08Sr0.02K0.01)(Cu2+0.89Mn3+0.11)Al4.00(Al5.56Mn2+1.71Mn3+0.37Fe3+0.31Mg0.04)
T1(□3.83Si0.17)T2(□1.00)[Si2.00O7]4[Si1.00O4]10O1.00([OH]8.45F0.55)

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

mineral PPL (lower
polar rotation)
PPL
(stage rotation)
XP
(stage rotation)
optic figure
(stage rotation)
cyprine/manganvesuvianite
PPL: magenta/red/pale yellow pleochroism, high relief;
XP: up to 1st order red-purple δ, partially masked by body color of mineral and by strong anomalous blue/brown overtones;
open-space filling with opaque hausmannite

 



left image: unpolarized light; right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-335
locality: Le Novelle Quarry, Ercolano, Monte Somma, Somma-Vesuvius Complex, Naples, Campania, Italy.
rock type: sanidinite facies metasomatized metacarbonate ejecta.
major mineralogy: The specimen was acquired for marialite, “apatite”, “mica” and calcite.

 



left image: unpolarized light; right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-336
locality: Le Coreux, Salmchâteau, Vielsalm, Stavelot Massif, Belgium.
rock type: braunite-[Mn-rich andalusite-group]-muscovite schist.
major mineralogy: Large porphyroblasts of zoned vuggy Mn-rich andalusite cores overgrown with later clean kanonaite rims occur abundantly in the sample. The porphyroblasts are easiest to recognize in the portions of the sample dominated by massive fine-grained muscovite intergrown with fine quartz (and free of opaque Mn minerals), but also occur within the portions of the sample additionally rich with small grains of braunite (and appear almost uniformly black in hand sample; but in this part of the sample the andalusite porphyroblasts can be seen with BSE imaging). A variety of additional accessory minerals occur as variably abundant scattered tiny grains with the braunite-rich portions of the sample. These accessory minerals include Mn-bearing hematite, cerianite-(Ce), possible As-bearing wakefieldite-(Ce), and a poorly-quantified mildly-REE-enriched [Mn+V+Al]-silicate reminiscent of perhaps ardennite (at least, it could be approximately normalized to an ardennite-like formula, allowing for some generous assumptions on the valence distribution of the V, possible unanalyzed As, and the possibility of hypothetical transition metal end-members). All of the ambiguity unfortunately is a result of each of these various accessory mineral grains being exceedingly tiny (most under 20 microns), and so it was difficult to ensure the beam was centered on the grain of interest and not overlapping other material adjacent or underneath; thus, analyses of these small grains are not unequivocally of single minerals. This thin section (or better yet, duplicate thin sections from the existing billet or from additional samples) would benefit from additional study.

mineral representative mineral compositions in FKM-336
hematite (Fe3+1.95Mn3+0.04)O3
cerianite-(Ce) not quantitatively analyzed
wakefieldite-(Ce)?
(sparse very small grain; could be something else or a mixture)
(Ce0.26Y0.18Nd0.17Ca0.16[HREE]0.07?Gd0.04Pr0.03FeT0.83La0.02Th0.01)[V0.83As0.16Si0.01O4]
braunite (abundant very small grains) (Mn2+0.83Mg0.07Ca0.05Cu0.03Na0.01Co0.01Zn0.01K0.01)(Mn3+5.17Fe3+0.63Al0.17Ti0.02)O8[Si0.95P0.03Al0.02O4]
kanonaite-dominant andalusite-
group ss (clean rims)
(Mn3+0.73Al0.21Fe3+0.05)Al1.00O1.00[Si0.99Al0.01O4]
andalusite-dominant anadalusite-
group ss (vuggy cores; “viridine”)
(Al0.70Mn3+0.27Fe3+0.02)Al1.00O1.00[Si0.98Al0.02O4]
ardennite-(V)? or similar?
(sparse very small grain; could be
something else or a mixture)
(Mn2+2.89Na0.38Ce0.14Ca0.13Nd0.11Fe2+0.10La0.07Y0.05Pr0.03Sm0.02Gd0.02Th0.02Zn0.01)
Al4.00(V3+1.12Fe2+0.57Al0.25Mg0.04Ti0.03)
[V5+0.78As5+0.22?O4][Si1.00O4]2[Si2.61Al0.39O10]([OH]5.97O0.03)
muscovite (“illite”) (K0.67Na0.150.18)(Al1.95FeT0.06Mg0.03MnT0.010.95)[Si3.09Al0.91O10]([OH]1.97F0.03)
quartz not analyzed

accompanying videos: Short videos featuring the mineral associations and optical properties of the kanonaite/Mn-rich andalusite in this thin section offer a more detailed look at this sample.

mineral PPL (lower
polar rotation)
PPL
(stage rotation)
XP
(stage rotation)
optic figure
(stage rotation)
kanonaite rims/Mn-rich andalusite cores
PPL: yellow-green/deep bluish-green/deep yellow-orange pleochroism, high relief;
XP: birefringence color masked by body color of mineral;
with muscovite

 



left image: unpolarized light; right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-337
locality: Graulay, Hillesheim, Vulkaneifel, Rhineland-Palatinate, Germany.
rock type: late stage cavity filling in nephelinite.
major mineralogy: The specimen was acquired for melilite, nepheline, skeletal perovskite, magnetite and fluorapatite.

 



left image: unpolarized light; right image: under crossed polarizers; use slider in center to view more of either image

under shortwave ultraviolet [SWUV] illumination

 
sample: FKM-338 (billet courtesy of V. King [Rochester, NY])
locality: Hpakant-Tawmaw jade tract, Kachin state, Burma.
rock type: blueschist to eclogite facies jadeitite.
major mineralogy: The specimen was acquired for chromian epidote.

 



left image: unpolarized light; right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-339 (billet from Univ. Arizona petrology collection; sample 7-28-60-15 [the 15th sample added to the collection on 28 July 1960])
locality: The locality is listed as “Ogilby, CA”, although this now-abandoned town likely just represented a convenient nearby road/railroad point-of-access for the mines in the Cargo Muchacho Mountains a few kilometers to the NE. The probable actual locality is on the western edge of the Cargo Muchacho Mountains, from one of the quarry exposures at Vitrefrax Hill/Bluebird Hill, where kyanite was mined for refractory purposes.
rock type: a moderate-grade metamorphosed equivalent of an advanced argillic metasomatic assemblage.
major mineralogy: The specimen was acquired for pyrophyllite, kyanite and lazulite (and/or dumortierite).

 



left image: unpolarized light; right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-340 (billet from the Univ. Arizona mineralogy collection; sample was orphaned and subsequently dis-used)
locality: unknown, but presumably from one of the chromite deposits of eastern Turkey that abundantly supplied attractive purple “kämmererite” specimens to the mineral specimen collector market in the 1980s/1990s; possible localities include the Guleman Mines in Elazig Province, or perhaps more likely one of the two more famous mines in the Kop Daglari area in Erzurum Province.
rock type: The sample is an altered chromatite traversed by veins of “kämmererite” (chromian clinochlore).
major mineralogy: Relatively [Mg+Al]-enriched magnesiochromite dominates the specimen, and makes up much of the cores to many of the “chromite” (sensu lato) grains; many of these have a “vuggy” texture. A later, more [Fe+Cr]-enriched and “cleaner” magnesiochromite overgrows the core material. Locally along cracks and between grain boundaries in the main “chromite”, irregular patches of variable composition chromite (sensu stricto) grow into the earlier magnesiochromite; these patches presumably represent alteration roughly contemporaneous with the growth of chlorite veining. The chlorite occurs in distinct both high-Cr and low-Cr clinochlore compositions, optically similar under plane-polarized light (although surprisingly more pale-colored in thin section than expected from the more saturated hand sample colors). However, the two main compositions are optically readily differentiable under crossed polarizers by a strong “Berlin” blue (and with subordinate ocher-brown) anomalous birefringence in the high-Cr chlorite, and only overtones of anomalous brown on the baseline 1st order gray to white birefringence observed in the low-Cr chlorite (see the accompanying videos below). In places the two compositions appear to be intergrown, but also elsewhere veinlets of the high-Cr chlorite overgrow and crosscut the low-Cr chlorite. The low-Cr clinochlore appears fairly compositionally homogeneous, whereas the high-Cr shows weak irregular compositional zoning. One small grain of awaruite was observed in the “chromite” and this is presumably another secondary product in the rock (for example, through reduction of a primary Ni-Fe sulfide by hydrogen produced by nearby serpentinization reactions).

mineral representative mineral compositions in FKM-340
awaruite Ni0.75Fe0.23Cu0.01
magnesiochromite-dominant
spinel group ss
(main central zones; most [Mg+Al]-rich)
(Mg0.66Fe2+0.35)(Cr1.41Al0.52Fe3+0.05)O4
magnesiochromite-dominant
spinel group ss
(clean outer zones; most [Fe+Cr]-rich)
(Mg0.59Fe2+0.41Mn2+0.01)(Cr1.64Al0.27Fe3+0.07)O4
chromite-dominant spinel group ss
(patchy; most [Mg+Cr]-rich)
(Fe2+0.63Mg0.38Mn2+0.01)(Cr1.85Fe3+0.08Al0.03Ti0.01Si0.01)O4
chromite-dominant spinel group ss
(patchy; most Fe-rich)
(Fe2+0.90Mg0.08Mn2+0.02)(Cr1.69Fe3+0.27Al0.03Ti0.01)O4
high-Cr clinochlore (strong anomalous
blue±ocher δ; most [Mg+Si]-rich)
(Mg4.94Cr0.57Al0.27FeT0.100.11)[Si3.36Al0.63O10](OH)8.00
high-Cr clinochlore (strong anomalous
blue±ocher δ; most [Fe+Cr]-rich)
(Mg4.84Cr0.67Al0.22FeT0.180.09)[Si3.25Al0.75O10](OH)8.00
high-Cr clinochlore (strong anomalous
blue±ocher δ; most VIAl-rich)
(Mg4.83Cr0.54Al0.38FeT0.110.14)[Si3.32Al0.67O10](OH)8.00
low-Cr clinochlore (weak anomalous
brown tint on 1st order white δ)
Na0.02(Mg4.69Al0.88Cr0.21FeT0.09Ni0.030.10)[Si3.04Al0.96O10](OH)8.00

accompanying videos: Short videos featuring the mineral associations and optical properties of both the high-Cr clinochlore and low-Cr clinochlore in this thin section offer a more detailed look at this sample.

mineral PPL (lower
polar rotation)
PPL
(stage rotation)
XP
(stage rotation)
optic figure
(stage rotation)
high-Cr clinochlore (“kammererite”?)
PPL: very pale yellowish-pink, moderate relief;
XP: strong anomalous blue/ocher-brown birefringence;
with low-Cr chlorite and chromite (sensu lato)
no optic figure of useful quality was available
low-Cr clinochlore (“kammererite”?)
PPL: very pale yellowish-pink, moderate relief;
XP: up to 1st order white δ, with anomalous brown overtones;
with high-Cr chlorite and chromite (sensu lato)

 




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sample: FKM-341
locality: sub-locality #4, at Mautia Hill, Kongwa, Kongwa District, Dodoma Region, Tanzania.
rock type: whiteschist-associated UHP metamorphic rock.
major mineralogy: The specimen was acquired for edenite.

 




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sample: FKM-342
locality: boulder field of ejected volcanic bombs, east of the Ol Doinyo Lengai natrocarbonatite volcano, Ngorongoro District, Arusha region, Tanzania.
rock type: carbonatite-associated combeite-wollastonite nephelinite bombs.
major mineralogy: The specimen was acquired for combeite, wollastonite, nepheline and augite.

 




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sample: FKM-343
locality: White Cloud pegmatite, South Platte, Jefferson Co., CO, USA.
rock type: REE-bearing granite pegmatite.
major mineralogy: The specimen was acquired for thalénite-(Y), yttrofluorite, allanite-(Ce) and bastnäsite-(Ce).

 




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sample: FKM-344 (billet courtesy of B. Widener, Univ. Arizona [thanks for the cool sample, Brandon!])
locality: Gun claim, located 4 km SE of Wilson Lake, 16 km SE of Itsy Mountain and 155 km NE of Ross River, Yukon, Canada.
rock type: test.
major mineralogy: The specimen was acquired for muirite and sanbornite.

 




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sample: FKM-345 (billet courtesy of B. Widener, Univ. Arizona [thanks for the cool sample, Brandon!])
locality: the label states “High Pellice valley, Massif of Monviso, Piedmont Italy”, but this location is a bit problematic because the head of the Pellice Valley is not within the Monviso Massif and at best only abuts its northern margin. Chromian omphacite-bearing jadeitite is well known from Neolithic-age quarries on Monviso (Monte Viso) as a source of “Alpine jade” axeheads and tools, but the online “chatter” among the mineral collector community selling similar material suggests this is a much more recent find. One online dealer specifically describes samples of “chrome-omphacite with gedrite”, and with a “polished surface” (apparently with a polished window is how these new samples are hitting the market), from a new find in the Italian Alps. The locality is denoted as being near Rifugio Barbara Lowrie [~44.75N ~7.08E], Monte Comba Carbonieri area, [~7 km SSW of Bobbio Pellice], Pellice Valley, Piedmont, Italy (note: the bracketed portions above are a few additional geo-locaters I’m including for extra detail). Between the physical description of the material, the location of Rifugio Barbara Lowrie in the “High Pellice Valley”, and the recognition that material from a new find is currently hitting the market, it is strongly believed this sample is indeed from this new Rifugio Barbara Lowrie locality.
rock type: test.
major mineralogy: The specimen was acquired for chromian omphacite/jadeite; if the presumed locality is correct, gedrite has also been reported from this material.

 




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sample: FKM-346
locality: Mont Saint-Hilaire, Montérégie, Québec, Canada.
rock type: nepheline syenite.
major mineralogy: The specimen was acquired for normandite.

 




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sample: FKM-347
locality: from an unspecified locality in the region of Lleida (Lérida), Catalonia, Spain.
rock type: test.
major mineralogy: The specimen was acquired for aerinite.

 




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sample: FKM-348
locality: Gjerdingselva, Nordmarka, Lunner, Oppland, Norway.
rock type: test.
major mineralogy: The specimen was acquired for gagarinite-(Y). Note: gagarinite-(Y) is reportedly decomposed by water, so the thin section was prepared using a non-aqueous fluid.

 




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sample: FKM-349
locality: Bellerberg volcano, Ettringen, Eifel Volcanic Fields, Germany.
rock type: test.
major mineralogy: The specimen was acquired for calcio-olivine and portlandite. Note: portlandite is slightly soluble in water, so the thin section was prepared using a non-aqueous fluid.

 




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sample: FKM-350
locality: Xianghualing Mine, Xianghualing Sn-polymetallic ore field, Linwu Co., Chenzhou, Hunan, China.
rock type: phlogopite-rich greisen-like skarn developed in metamorphosed limestone intruded by granite.
major mineralogy: The specimen was acquired for hsianghualite, phlogopite, and possibly additional rarer Be and Li minerals.

 



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