samples FKM-226 to FKM-250

 

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.

Note: Depending on the speed of your internet connection, it could take a minute or two for the images to load.

 


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.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-226
iron Fe0.98Ni0.02Co0.01
copper (most Cu-rich) Cu0.98Fe0.01Ni0.01
copper (most Fe+Ni-rich) Cu0.94Fe0.04Ni0.02
cohenite (Fe2.98Ni0.02)C
troilite Fe1.00S1.00
hercynite (Fe2+0.84Mg0.16Zn0.01)(Al1.94Fe3+0.03Ti0.01)O4
hematite (Fe3+1.95Fe2+0.02Si0.02Mn2+0.01)O3
ilmenite (Fe2+0.91Mg0.07Mn2+0.01Ti0.01)Ti1.00O3
forsterite-rich ol ss
(most Mg-rich inner zone)
(Mg0.99Mn2+0.01)(Fe2+0.93Mg0.07)[Si1.00O4]
fayalite-rich ol ss
(main Fe-rich outer zone)
(Mg0.59Fe2+0.39Mn2+0.01)Fe2+1.00[Si1.00O4]
fayalite-rich ol ss
(most Fe-rich outermost rim)
(Fe2+0.68Mg0.30Mn2+0.02)Fe2+1.00[Si1.00O4]
pigeonite (Mg0.87Ca0.12Mn2+0.02)(Fe2+0.76Mg0.22Al0.01Ti0.01)[Si1.99Al0.01O6]
augite (Ca0.67Mg0.30Na0.02Mn2+0.01)(Mg0.55Fe2+0.40Ti0.04)[Si1.94Al0.06O6]
chamosite (or likely a chlorite
+smectite interlayer phyllosilicate)
(Ca0.19Na0.01)(FeT3.13Mg1.29Al0.80MnT0.020.76)[Si3.36Al0.64O10]([OH]7.97Cl0.03)
sanidine? (most K-rich) (K0.79Na0.16Ca0.01)[Si2.97Al1.03Fe3+0.01O8]
sanidine? (most Na-rich) (K0.68Na0.27Ca0.01Ba0.01)[Si2.94Al1.05Fe3+0.01O8]
“labradorite”-rich plag ss
(most Ca-rich cores)
(Ca0.69Na0.30K0.01)[Si2.28Al1.69Fe3+0.02O8]
“andesine”rich plag ss
(most Na-rich rims)
(Na0.61Ca0.35K0.03)[Si2.61Al1.36Fe3+0.02O8]

 



sample: FKM-227
locality: Eveslogchorr Mtn., Khibiny massif, Kola Peninsula, Russia.
rock type: agpaitic nepheline syenite.
major mineralogy: specimen acquired for astrophyllite.
(left: unpolarized light; right: under crossed polars)

 



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).
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-228
hematite (Fe3+1.95Cr0.01Ti0.01Fe2+0.01Mn2+0.01)O3
M2Mn-senaite” (Pb0.71Sr0.26Ba0.05Ce0.01)(Mn2+0.96Ca0.02Sc0.01)(Mn2+1.51Zn0.37Fe2+0.08Mg0.02Co0.02)
(Ti13.90Fe3+3.92Sb5+0.05V3+0.04Al0.03Cr0.02Sn0.01)O38
rutile (Ti0.94Fe3+0.02Sb5+0.01Si0.01)O2
calcite (Ca0.69Mn2+0.26Mg0.04Sr0.01)[CO3]
kutnohorite (Ca0.99Sr0.01)(Mn2+0.77Mg0.13Ca0.10)[CO3]2
gasparite-(Ce) (Ce0.51La0.29Nd0.12Pr0.05Ca0.03Sm0.01Sr0.01)[As0.86V0.06P0.05O12]
chernovite-(Y) (core) (Y0.81[Gd+HREE]~0.05Sm0.05Ca0.04Nd0.03Ce0.01)[As0.98V0.01O12]
chernovite-(Y) (rim) (Y0.45Nd0.18Ce0.13[Gd+HREE]~0.07Sm0.06Ca0.06Pr0.02La0.02)[As0.98V0.03O12]
berzeliite-rich
berzeliite series ss
(Ca1.92Na0.91Mn2+0.16)(Mg1.03Mn2+0.78V3+0.18)[As2.98Si0.01O12]
manganberzeliite-rich
berzeliite series ss
(most [Mn+Na]-rich)
(Ca1.93Na0.94Mn2+0.12)(Mn2+1.20Mg0.64V3+0.15)[As2.88V5+0.10Si0.02O12]
manganberzeliite-rich
berzeliite series ss
(most V-rich)
(Ca1.94Na0.92Mn2+0.13)(Mn2+1.17Mg0.69V3+0.14)[As2.72V5+0.26Si0.01O12]
“Na2Ca3Mn3[AsO4]4(OH)2 . 6H2O”? (Na1.96Mn2+0.04)Ca3.00(Mn2+2.58Mg0.32V3+0.10)[As3.86V5+0.12Si0.02O16]([OH]1.94O0.06) . 6H2O
fluorapatite (low z
primarily isolated grains)
(Ca4.97Sr0.01Na0.01)[P2.99Si0.01O12](F0.67[OH]0.33)
fluorapatite-rich
apatite ss (low z cores)
(Ca4.92Sr0.03Mn2+0.02Ce0.01)[P2.60As0.40O12](F0.56[OH]0.44)
fluorapatite-rich
apatite ss (mod z)
(Ca4.88Sr0.04Mn2+0.04Ce0.02Na0.01)[P2.26As0.73O12](F0.64[OH]0.36)
hydroxylapatite-rich
apatite ss (mod z)
(Ca4.89Sr0.05Mn2+0.04Ce0.02Na0.01)[P2.28As0.71O12]([OH]0.59F0.41)
hydroxylapatite-rich
apatite ss (high z zones)
(Ca4.81Sr0.08Mn2+0.07Ce0.01Na0.01)[P1.84As1.15O12]([OH]0.59F0.41)
titanite (low z zones) (Ca0.98Mn2+0.01)(Ti0.95Fe3+0.03Al0.01V0.01)(O0.98[OH]0.01F0.01)[Si0.97As0.03Al0.01O4]
titanite (mod z zones) (Ca0.98Mn2+0.02Na0.01)(Ti0.95Fe3+0.03Sb5+0.01V0.01)(O0.95[OH]0.04F0.01)[Si0.96As0.02Al0.01Fe3+0.01O4]
titanite (high z zones) (Ca0.97Mn2+0.02Na0.01)(Ti0.93Fe3+0.05Sb5+0.02V0.01)(O0.95[OH]0.05F0.01)[Si0.95As0.04Al0.01O4]
talc (Mg2.90MnT0.02Al0.01Zn0.01Co0.01Ni0.010.04)[Si4.00O10]([OH]1.96F0.04)
albite (Na0.99Ca0.01K0.01)[Si2.98Al1.01Fe3+0.02O8]

 



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.
(left: unpolarized light; right: under crossed polars)

 



sample: FKM-230
locality: Madagascar (a more specific locality is not identified, but the sample resembles material from the Ampanihy rhodonite deposit.
rock type: test.
major mineralogy: specimen acquired for rhodonite, Mn-oxides and spessartine.
(left: unpolarized light; right: under crossed polars)

 



sample: FKM-231
locality: Mendes Pimentel, Minas Gerais, Brazil.
rock type: test.
major mineralogy: specimen acquired for brazilianite.
(left: unpolarized light; right: under crossed polars)

 



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.
(left: unpolarized light; right: under crossed polars)

 



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: test.
major mineralogy: specimen acquired for spinel (however from the scanned images, the isotropic mineral appears to be garnet).
(left: unpolarized light; right: under crossed polars)

 



sample: FKM-234
locality: Russia (a more specific locality is not identified, but the sample resembles the “Orlets”-type material from the famous rhodonite mines of the Ekaterinburg area, Middle Urals).
rock type: test.
major mineralogy: specimen acquired for rhodonite.
(left: unpolarized light; right: under crossed polars)

 



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.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-235
magnetite (Fe2+0.94Mg0.05Mn2+0.01)(Fe3+1.97Al0.02Fe2+0.01)O4
hematite
(exsolution in magnetite)
(Fe3+1.85Fe2+0.04Ti0.04Al0.03V0.02Mg0.01)O3
ilmenite (Fe2+0.69Mg0.10Fe3+0.19Mn2+0.02)(Ti0.81Fe3+0.18V0.02)O3
rutile? (alteration?
lamellae in ilmenite)
(Ti0.82Fe3+0.15V0.02)O2
fluorapatite (Ca4.88Fe2+0.03Na0.01Ce0.01Nd0.01Y0.01)[P2.98Si0.02O12](F0.68[OH]0.30Cl0.02)
forsterite (Mg0.98Mn2+0.01)(Fe2+0.79Mg0.20Fe3+0.01)[Si0.99Fe3+0.01O4]
“hypersthene” (core) (Mg0.91Ca0.08Mn2+0.01)(Fe2+0.57Mg0.39Fe3+0.03Ti0.01)[Si1.94Al0.04Fe3+0.02O6]
“hypersthene” (rim) (Mg0.91Ca0.07Mn2+0.02)(Fe2+0.73Mg0.23Fe3+0.03Ti0.01)[Si1.95Fe3+0.03Al0.02O6]
pigeonite?
(see text)
(Mg0.85Ca0.13Mn2+0.02)(Fe2+0.62Mg0.34Fe3+0.03Ti0.01)[Si1.94Fe3+0.03Al0.02O6]
augite (Ca0.72Mg0.24Na0.02Mn2+0.01)(Mg0.64Fe2+0.27Fe3+0.06Ti0.02)[Si1.91Al0.08Fe3+0.01O6]
“bytownite” plag ss (core) (Ca0.81Na0.19Sr0.01)[Si2.19Al1.79Fe3+0.02O8]
“labradorite” plag ss (inner rim) (Ca0.49Na0.49K0.03Sr0.01)[Si2.51Al1.46Fe3+0.04O8]
“andesine” plag ss (outer rim) (Na0.65Ca0.25K0.08)[Si2.75Al1.22Fe3+0.02O8]

 



sample: FKM-236
locality: Jakobsberg Mine, Jakobsberg ore field, Nordmark district, Filipstad, Värmland, Sweden.
rock type: test.
major mineralogy: specimen acquired for barylite, hausmannite and calcite
(left: unpolarized light; right: under crossed polars)

 



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.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-237
sphalerite normalization pending
pyrite Fe0.99S2.00
pyrite (most As-rich) Fe0.99(S1.96As0.04)
ilmenite (most Fe-rich) (Fe2+0.69Mn2+0.29Fe3+0.02)(Ti0.96Nb0.02Fe2+0.02)O3
ilmenite (most Mn-rich) (Fe2+0.51Mn2+0.47V0.01)(Ti0.99Nb0.02)O3
magnetite (most Fe-rich) (Fe2+0.88Mn2+0.11Zn0.01)(Fe3+1.45Ti0.26Fe2+0.26Al0.02V0.01)O4
magnetite (most Ti-rich) (Fe2+0.83Mn2+0.15Zn0.01Mg0.01)(Fe3+1.28Ti0.35Fe2+0.35Al0.02)O4
loparite-(Ce) (Na0.58Ce0.19La0.12Ca0.06Nd0.02Pr0.01FeT0.01)(Ti0.76Nb0.23Ta0.01)O3
bastnäsite-(Ce) normalization pending
fluorapatite (Ca4.66Ce0.09Na0.06La0.05Nd0.05Pr0.02Fe2+0.02Y0.01Sm0.01Gd0.01[HREE]0.01Mn2+0.01)
[P2.73Si0.26S0.01O12](F0.71[OH]0.29)
monazite-(Ce) (Ce0.54La0.19Nd0.18Pr0.06Sm0.02Th0.01)[P0.97Si0.03O4]
titanite (Ca0.93Ce0.02Na0.01Nd0.01Mn2+0.01Y0.01)(Ti0.90Fe3+0.06Al0.02Nb0.01Zr0.01)(O0.96F0.04)[Si0.98Al0.02O4]
aegirine-rich cpx ss
(#90; main; most Na+Ti-rich)
(Na0.91Ca0.08Mn2+0.01)(Fe3+0.66Fe2+0.12Ti0.11Mg0.05Al0.03Mn2+0.02Zr0.01)[Si1.97Al0.03O6]
aegirine-rich cpx ss
(#91; patches by #90; most Zr-rich)
(Na0.86Ca0.13Mn2+0.01)(Fe3+0.63Fe2+0.15Zr0.07Mg0.06Ti0.05Mn2+0.04Al0.01)[Si1.98Al0.02O6]
aegirine-augite-rich cpx ss
(#50; ~unzoned main)
(Na0.64Ca0.34Mn2+0.02)(Fe3+0.54Fe2+0.23Mg0.13Ti0.03Mn2+0.03Zr0.02Al0.02)[Si1.98Al0.02O6]
aegirine-augite-rich cpx ss
(#41; edge exterior to #40)
(Ca0.61Na0.38)(Fe3+0.36Mg0.33Fe2+0.22Mn2+0.05Ti0.02Al0.01)[Si1.96Al0.04O6]
diopside-rich cpx ss
(#40; center main)
(Ca0.86Na0.10Mn2+0.04)(Mg0.68Fe2+0.18Fe3+0.10Ti0.02)[Si1.95Al0.05O6]
~[fluoro-magnesio-arfvedsonite]-
[ferri-katophorite]* join-rich
oxo/NaCa/Na-amph ss (most Ca+Mg-rich)
(Na0.73K0.27)(Na1.26Ca0.74)(Na~0.06Mg3.28Fe2+0.77Fe3+0.53Mn2+0.26Ti0.06Al0.02Zn0.01Zr0.01)
[Si7.76Al0.24O22](F1.32[OH]~0.56O~0.12)
~[fluoro-ferri-nybøite]-[ferri-obertiite]*
join-rich oxo/NaCa/Na-amph ss
(Na0.76K0.24)(Na1.91Ca0.09)(Na~0.03Mg2.62Fe3+1.66Mn2+0.19Ti0.19Fe2+0.10Zn0.01~0.20)
[Si7.68Al0.32O22](F1.21[OH]~0.41O~0.37)
~[fluoro-ferri-nybøite]-[ferri-obertiite]*
join-rich oxo/NaCa/Na-amph ss
(most Fe+Ti-rich)
(Na0.77K0.23)(Na1.93Ca0.07)(Na~0.15Mg2.17Fe3+1.75Ti0.40Mn2+0.28Fe2+0.13Zn0.01~0.11)
[Si7.50Al0.50O22](F1.14O~0.80[OH]~0.06)
muscovite (K0.87Na0.030.10)(Al2.01FeT0.050.94)
[Si2.96Al1.04O10](OH)2.00
fluoro-phlogopite-rich trioct
mica ss (most Si+F-rich)
(K0.93Na0.10)(Mg1.82FeT0.70Ti0.17MnT0.09Al0.01Zn0.010.20)
[Si3.23Al0.77O10](F1.06[OH]0.60O0.35)
phlogopite-rich trioct mica ss
(main)
(K0.88Na0.12)(Mg1.67FeT0.95Ti0.26MnT0.080.04)[Si2.92Al1.07Fe3+0.01O10]([OH]0.80F0.69O0.52)
phlogopite-rich trioct mica ss
(most [OH]-rich)
(K0.860.14)(Mg1.58FeT1.33MnT0.05Ti0.020.02)[Si2.99Al0.99Fe3+0.02O10]([OH]1.64F0.32O0.04)
annite-rich trioct mica ss
(most Fe+Mn-rich)
(K0.88Na0.06Ca0.010.05)(FeT1.60Mg0.95Ti0.24MnT0.17Zn0.010.03)
[Si2.95Al1.00Fe3+0.05O10]([OH]1.30O0.47F0.22)
mesoperthite
(patchy orthoclase component)
(K0.96Na0.05)[Si2.98Al1.02O8]
mesoperthite
(patchy albite component)
(Na1.00K0.01)[Si2.98Al1.01O8]
analcime (Na0.94K0.010.05)[Si1.99Al1.01O6] . H2O

 



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.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-238
pyrrhotite Fe0.91S1.00
sphalerite (Zn0.78Fe0.22)S1.00
gersdorffite
(most Fe-rich)
(Ni0.75Fe0.25)(As0.97Sb0.03)(S0.87As0.13)
gersdorffite
(most Co+Sb-rich)
(Ni0.74Fe0.24Co0.01)(As0.96Sb0.05)(S0.86As0.15)
calcite (Ca0.96Mg0.04)[CO3]
dolomite Ca1.00(Mg0.98Ca0.01)[CO3]2
barite (poor stoichiometry;
re-analysis warranted)
(Ba1.03Na0.01)[S0.94O4]
fluorapatite-rich
apatite ss
Ca4.88[P2.99Si0.01O12](F0.53[OH]0.46Cl0.01)
hydroxylapatite-rich
apatite ss
Ca4.94[P3.00O12]([OH]0.51F0.47Cl0.02)
forsterite Mg1.00(Mg0.98Fe2+0.01)[Si0.99Fe3+0.01O4]
“cherchiaraite-like”
mineral? (see text)
(Ba3.80Ca0.17Na0.03)Mg4.07(OH)6
[Si3.97Al0.02As5+0.01O12][Al1.97Fe3+0.03O(OH)6]([OH]~0.68Cl0.38F0.07~0.87) . Ba0.49
diopside Ca0.99Mg1.00[Si1.99Fe3+0.01O6]
tremolite (Na0.020.98)(Ca1.98Na0.02)(Mg4.93V0.03Fe3+0.03Al0.01)[Si7.91Al0.09O22]([OH]1.93F0.06O0.01)
kinoshitalite
(most Ba-rich; cores)
(Ba0.89K0.08Na0.04Ca0.01)(Mg2.74Ti0.09V0.08FeT0.03Al0.010.05)[Si2.08Al1.91O10]([OH]1.49F0.31O0.18Cl0.02)
kinoshitalite
(most K+Mg-rich; rims)
(Ba0.63K0.12Na0.05Ca0.010.19)(Mg2.90Ti0.04V0.02FeT0.020.02)[Si2.52Al1.48O10]([OH]1.62F0.29O0.08Cl0.01)
“serpentine”
(enclosing tremolite)
Ca0.01(Mg5.77Al0.04FeT0.03V0.020.14)[Si4.04O10]([OH]7.99Cl0.01)
“serpentine”
(enclosing forsterite)
Ca0.01(Mg5.83FeT0.070.10)[Si4.02O10]([OH]7.96Cl0.03F0.01)

 



sample: FKM-239
locality: Raidlgraben, Fritzbach valley, Pöham, Werfen, Salzburg, Austria.
rock type: test.
major mineralogy: specimen acquired for lazulite.
(left: unpolarized light; right: under crossed polars)

 



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.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-240
osumilite (K0.670.33)(Na0.011.99)(Fe2+0.95Mg0.85Mn2+0.14Fe3+0.04Ca0.01)(Al2.69Fe3+0.31)[Si10.25Al1.75O30]

 



sample: FKM-241
locality: Lågendalen, Hedrum, Larvik, Vestfold, Norway.
rock type: test.
major mineralogy: specimen acquired for catapleiite.
(left: unpolarized light; right: under crossed polars)

 



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.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-242
iwakiite (Mn2+0.71Mg0.27Zn0.01)(Fe3+1.10Mn3+0.77Al0.11Mn2+0.02)O4
calcite (Ca0.92Mn2+0.04Mg0.04)[CO3]
dolomite (Ca0.99Mg0.01)(Mg0.90Mn2+0.10)[CO3]2
barytocalcite Ba1.02(Ca0.95Pb0.02Sr0.01Mn2+0.01)[CO3]2
norsethite Ba1.01(Mg0.92Mn2+0.04Ca0.03Na0.01)[CO3]2
fredrikssonite (Mg1.90Mn2+0.11)(Mn3+0.55Fe3+0.38Al0.06)O2[BO3]
barite Ba0.99[S1.00O4]
adelite (Ca0.95Pb0.02Mn2+0.02)Mg1.00([OH]0.99O0.01)[As0.99P0.01O4]
hydroxylapatite (most Pb-rich) (Ca4.93Mn2+0.03Pb0.02Ce0.01)[P2.26As0.73O12]([OH]0.68F0.28Cl0.04)
hydroxylapatite (most As-rich) (Ca4.93Mn2+0.04Pb0.01Ce0.01)[P2.14As0.86O12]([OH]0.71F0.23Cl0.05)
hydroxylapatite (most P-rich) (Ca4.96Mn2+0.02Fe3+0.01)[P2.44As0.54O12]([OH]0.74F0.25Cl0.02)
hydroxylclinohumite (Mg8.47Mn2+0.51Fe2+0.01Ca0.01)[Si3.93B0.07O15.93(OH)0.07]([OH]1.31F0.69)
kinoshitalite (high z core) (Ba1.01K0.01Ca0.01Na0.01)(Mg2.73Al0.10MnT0.06FeT0.060.05)[Si1.88Al2.12O10]([OH]1.93F0.06)
kinoshitalite (low z inner rim) (Ba0.87K0.15Ca0.04Na0.01)(Mg2.74Al0.08MnT0.06FeT0.050.07)[Si2.03Al1.97O10]([OH]1.96F0.04)
kinoshitalite (mod-low z outer rim) (Ba0.96K0.07Ca0.02Na0.01)(Mg2.77MnT0.05FeT0.05Al0.040.09)[Si2.02Al1.98O10]([OH]1.93F0.07)

 



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.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-243
linnaeite (Co2+0.95Mn2+0.03Cu0.01)(Co3+1.32Ni3+0.66Fe3+0.02)S4.00
cobaltite (Co0.99Ni0.01)As0.98S1.00
galaxite (most Al-rich) (Mn2+0.93Mg0.02Fe2+0.02Co0.02)(Al1.59Fe3+0.40)O4
galaxite (most Fe-rich) (Mn2+0.94Mg0.02Fe2+0.02Co0.01)(Al1.50Fe3+0.48V0.01Ti0.01)O4
jacobsite (most Al-rich) (Mn2+0.97Fe2+0.01Co0.01Ni0.01Zn0.01)(Fe3+1.46Al0.50V0.02Ti0.01)O4
jacobsite (most Fe-rich) (Mn2+0.94Fe2+0.06)(Fe3+1.84Al0.12V0.02Ti0.01)O4
rhodochrosite
(upper “cloudy” band)
(Mn2+0.96Ca0.02Fe2+0.02)[CO3]
rhodochrosite
(patches in kutnohorite)
(Mn2+0.87Ca0.13)[CO3]
kutnohorite (Ca0.82Mn2+0.17Mg0.01)Mn2+1.00[CO3]2
fluorapatite (Ca4.82Mn2+0.16Sr0.02)[P2.99As0.01O12](F0.67[OH]0.33)
alleghanyite (Mn2+4.81Mn3+0.10Mg0.07Ti0.03Ca0.01)[Si1.96Fe3+0.04O4]([OH]1.63F0.37O0.05)
manganhumite (Mn2+6.63Mn3+0.13Mg0.11Ti0.04Fe3+0.01Co0.01Ca0.01)[Si2.94Fe3+0.06O4]([OH]1.48F0.52O0.08)
kellyite (most Mn-rich) (MnT3.77Al1.87Mg0.21FeT0.14Co0.01)[Si2.02Al1.98O10](OH)8.00
kellyite (most Mg+Fe-rich) (MnT3.40Al1.96Mg0.41FeT0.21Co0.02)[Si2.01Al1.99O10](OH)8.00
“Ca-stilpnomelane” (Ca0.60Na0.05K0.010.34)(FeT6.80MnT0.39Al0.07Mg0.06Ti0.03Co0.010.64)
[Si11.99S0.01O~30]([OH]~5.98F0.02) . ~5H2O

 



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.
(left: unpolarized light; right: under crossed polars)

 



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.
(left: unpolarized light; right: under crossed polars)

 



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.
(left: unpolarized light; right: under crossed polars)

 



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.
(left: unpolarized light; right: under crossed polars)

 



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.
(left: unpolarized light; right: under crossed polars)

 



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: nepheline sodalite syenite.
major mineralogy: specimen acquired for nepheline, sodalite and aegirine.
(left: unpolarized light; right: under crossed polars)

 



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.
(left: unpolarized light; right: under crossed polars)

 



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