samples FKM-26 to FKM-50


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

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

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sample: FKM-26
locality: Merelani Hills, Lelatema Mtns., Simanjiro district, Manyara region, Tanzania.
rock type: diopside “skarn”. Granulite facies calc-silicate with retrograde amphibolite facies overprinting; possibly a meta-marl, with accompanying metasomatism; see the Ph.D. dissertation of Oliver (2006) for details on the geology of the Merelani area and the petrogenesis of the tanzanite/tsavorite mineralization.
major mineralogy: Mostly vanadian diopside with minor vanadian A-site-vacant calcic amphibole (straddling the nomenclature boundary between tremolite and magnesio-hornblende), graphite, sparse zoned titanite (up to 0.15 apfu V; more enriched in V than titanite from sample FKM-1, also from Merelani) and scattered calcite. Rare mukhinite and sulvanite were observed during microprobe examination of the original polished billet but were not found in this prepared thin section (however, mukhinite is also present in sample FKM-92, and so may be more widespread in V-rich metasomatic rocks than typically reported). There’s also a mineral present in the original billet (but also not observed in this prepared thin section) with a chemistry atypical of the other identified minerals. The major element composition is (all in wt%): F 2.6; Al 6.7; Si 15.5; Ca 25.4; V 9.2; Cr 0.3. Adding in minor Ti, Mg, Y and Sc (the sum of these totals to less than 0.36 wt%, most of which is Ti), it can be normalized to possibly an unusual vanadian vesuvianite (although the various site fillings are rather poor… total with estimated H2O ~98.7 wt%), or alternatively, and with better site fillings, to a vanadian fluor-hydrogrossular (total with estimated H2O ~99.2 wt%). More of this material will be sought in what remains of the billet to hopefully improve its characterization. The analyses listed below are taken from both the original polished billet and from the thin section subsequently prepared from it. Although the minor mineralogy between the two materials somewhat differs due to slight sample heterogeneity, for completeness, the mineral list encompasses both materials.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-26
“fluor-hydrogrossular”? (Ca2.97Y0.01)(Al1.12V0.84Cr0.03Ti0.02)[Si2.57Al0.040.39O10.44(OH)0.91F0.65]
titanite (core) (Ca0.98Y0.02[REE]0.01)(Ti0.83V0.09Al0.08)(O0.92F0.05[OH]0.03)[Si0.99Al0.01O4]
titanite (rim) (Ca0.98Y0.01[REE]0.01)(Ti0.78V0.13Al0.08)(O0.93F0.04[OH]0.03)[Si1.01O4]
mukhinite (needs re-analysis) Ca1.00Ca0.93(Al0.52V0.24Cr0.22)Al1.00(V0.63Mg0.32Mn3+0.05)(O0.91F0.09)[Si2.05O7][Si1.03O4](OH)
diopside (Ca0.94Na0.05Mg0.01)(Mg0.89Al0.06V0.04)[Si1.95Al0.05O6]
tremolite-rich Ca-amph ss (Na0.09K0.040.87)(Ca1.94Na0.06)(Mg4.51V0.31Al0.14Sc0.01Ti0.01Cr0.01Mn2+0.01)
Ca-amph ss
phlogopite (K0.86Na0.010.13)(Mg2.75Al0.11V0.08Ti0.01Cr0.010.04)[Si3.00Al1.00O10]([OH]1.32F0.65O0.03)
clinochlore (Mg4.56Al0.99V0.26Cr0.030.16)[Si3.01Al0.99O10]([OH]7.83F0.16)


sample: FKM-27
locality: Kipawa alkaline complex, Les Lacs-du-Témiscamingue, Abitibi-Témiscamingue, Québec, Canada.
rock type: metamorphosed alkali syenite.
major mineralogy: This attractive coarse-grained red, black and white rock is composed primarily of eudialyte, K-bearing amphibole approximately along the fluoro-magnesio-arfvedsonite/fluoro-richterite join, and two alkali feldspars (albite and microcline, the latter sometimes showing evidence of a partially obliterated weakly perthitic texture). Scattered fluorite is also present (commonly as rims between eudialyte and feldspar), as is minor aegirine-augite. Rare aluminocerite-(Ce) occurs as inclusions in amphibole. Analytical notes: (1) the analytical total including estimated H2O and estimated HREE is only 95.62 wt% for the aluminocerite-(Ce), so this material warrants additional analyses; (2) the marked dispersion of the amphibole suggests a significant Fe3+ content. Analytical data on Na+Fe3+ amphiboles from other localities, such as that reported by Czamanske & Dillet, 1988 and more recently Kullerud et al., 2013 [← subscription required], suggest the possibility and perhaps likelihood of both vacancies and Na (and/or possibly Ca) within the octahedral strip of these types of amphiboles. This normalization approach is used here, and markedly improves some of the other site occupancies (notably the occupancy of the A-site); (3) for classifying the amphibole, the older scheme of Leake et al., 1997 is favored over the newer Hawthorne et al., 2012 scheme. The latter yields a name of ferri-katophorite based on its proposed C(Al+Fe3++2Ti) criteria coupled with the traditional A-site, B-site and Mg/(Mg+Fe2+) parameters. However, this name is inconsistent with the 1 apfu TAl present in katophorite; (4) due to potential vacancies in multiple sites, the possibility of variable OH, H2O and even H2O+, and the common issue of multiple valences of Fe and Mn, eudialyte is a challenging mineral to normalize. The normalization routine used here is ∑(T+Z+M3+M4)=29, although this still requires a number of additional assumptions, including reasonable estimates of Fe3+/∑Fe and OH/(O+OH) ratios; additionally, Hf has not been measured here and is assumed to be 0.01*Zr (wt%). Estimates for Fe3+/∑Fe, water content and HREE abundances were based on analytical data provided by Schilling et al., 2011 [← subscription required] for Kipawa eudialyte. The structural formulas presented below are based on typical cation site occupancies (for an overview of the eudialyte group, see Johnsen et al., 2003), but the cation partitionings have not been verified by X-ray work. For simplicity, the presented structural formulas only account for the possibilities of vacancies in the N-sites and potentially in M2, although vacancies may exist in other sites too. While the overall normalization results in permissible formulas, this material would benefit from additional characterization. Hence, given these caveats, when comparing these eudialyte compositions to those from other samples presented here, it is most prudent to look at the sum of each element, rather than the plausible but explicitly unverified site assignments. Sample FKM-65, also from the Kipawa complex, is similar to this sample but also contains significant mosandrite.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-27
(low analytical total;
re-analysis warranted)
(very weakly higher z;
estimated z̄ ≈ 15.23)
(very weakly lower z;
estimated z̄ ≈ 15.07)
aegirine-augite (Na0.52Ca0.48)(Fe3+0.46Mg0.31Fe2+0.10Al0.04Mn2+0.03Ca0.03Ti0.01Zr0.01)[Si1.98Al0.02O6]
[fluoro-richterite] join
(Leake et al., 1997)
microcline (K0.93Na0.05)[Si2.97Al1.02O8]
albite (Na1.00K0.01)[Si2.98Al1.02Fe3+0.01O8]


sample: FKM-28
locality: Betroka district, Tuléar province, Madagascar.
rock type: cordierite-opx-sapphirine-phlogopite gneiss. Perhaps a granulite equivalent to a K-metasomatized cordierite-anthophyllite rock, or perhaps a granulite facies sepiolitic/illitic metapelite or argillic (montmorillonite+kaolinite±chlorite) alteration assemblage?
major mineralogy: Sapphirine (in part rimmed by cordierite, which is in turn partially altered to an “Al-rich saponite” that shows a fairly consistent major element content but a seemingly variable water content), Al-rich enstatite, phlogopite and a P-bearing perthitic Na-rich K-feldspar (sanidine?) with oligoclase exsolution lamellae. Scattered large apatite and large zoned monazite are present, as well as minor zircon and secondary zeolitic alteration. For comparison, other sapphirine-bearing samples featured here include FKM-11 and FKM-23.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-28
fluorapatite (Ca4.91Na0.04Fe2+0.01La0.01Ce0.01Nd0.01)[P3.00O12](F0.85[OH]0.09Cl0.07)
monazite-(Ce) (core) (Ce0.42La0.17Nd0.16Th0.11Pr0.05Ca0.04Sm0.02Gd0.01Pb0.01[HREE]0.01Y0.01)[P0.92Si0.07S0.01O4]
monazite-(Ce) (inner rim) (Ce0.41La0.16Nd0.16Th0.11Pr0.05Ca0.04Sm0.01Gd0.01Pb0.01[HREE]0.01Y0.01)[P0.91Si0.08S0.01O4]
monazite-(Ce) (outer rim) (Ce0.42La0.19Nd0.14Ca0.08Th0.07Pr0.05Sm0.01Pb0.01Y0.01)[P1.00Si0.01O4]
cordierite (Mg1.98Fe3+0.02)(Al2.96Fe3+0.04)[Al1.07Si4.93O18] . Na0.01
enstatite Mg1.00(Mg0.75Al0.12Fe2+0.11Fe3+0.02)[Si1.85Al0.15O6]
sapphirine (Mg3.62Fe2+0.37)(Al8.39Mg3.52Fe3+0.07Ti0.01)O4[Al8.49Si3.51O36]
phlogopite (K0.95Na0.05)(Mg2.63Ti0.17FeT0.11Al0.09)[Si2.75Al1.25O10]([OH]1.07F0.58O0.34)
“Al-dominant saponite”?
(low H2O)
(Ca0.12K0.02Na0.01)(Al1.59Mg0.77FeT0.07MnT0.010.57)[Si3.24Al0.76O10]([OH]1.99F0.01) . ~3.3H2O
“Al-dominant saponite”?
(high H2O)
(Ca0.25K0.01Na0.01Ba0.01)(Al1.58Mg0.60FeT0.07MnT0.010.74)[Si3.38Al0.62O10]([OH]1.98F0.02) . ~7.9H2O
(sanidine? host)
(“oligoclase” lamellae)


sample: FKM-29
locality: Yukspor Mtn., Khibiny massif, Kola Peninsula, Murmanskaja Oblast’, Russia.
rock type: test.
major mineralogy: specimen acquired for eudialyte and titanite.
(left: unpolarized light; right: under crossed polars)


sample: FKM-30
locality: Woods mine, Tamworth, Darling Co., NSW, Australia.
rock type: sérandite-ungarettiite-quartz gneiss. Upper amphibolite facies manganiferous metasediment, with possible superimposed Na-metasomatism?
major mineralogy: The mineralogical characterization of this sample has been a challenge. The sample was originally acquired for “kôzulite”, a hydrous amphibole now officially re-named mangano-ferri-eckermannite (or potentially alternatively mangano-mangani-eckermannite, depending on whether Fe3+ or Mn3+ is dominant). However, re-examination of the amphibole in this sample suggests that much of what was previously identified to be “kôzulite” is in fact the anhydrous and optically somewhat similar mangano-mangani-ungarettiite. Note that compositionally, NaNa2(Mn2+2Mn3+3)[Si8O22]O2 (i.e. Mn2+-Mn3+-ungarettiite) is essentially indistinguishable from NaNa2(Mn2+4Mn3+)[Si8O22](OH)2 (i.e. Mn2+-Mn3+-eckermannite) based only on microprobe results, as H content and the overall charge of Mn would have to be determined by other analytical methods. Further complicating the amphibole characterization is that intergrown with the main mangano-mangani-ungarettiite is a K-dominant version that may be a new mineral but is otherwise chemically similar to the main material. Also of note is that the small amount of Li included in the two tabulated amphibole compositions is only an assumption and also needs to be verified by ICP-MS or SIMS; however, the estimated amounts markedly improve the overall normalizations, and would also not be inconsistent with slight solid solution toward leakeite/pedrizite compositions and the occurrence of sugilite at this locality. In addition to the one (or two?) amphibole species present, two (or possibly three?) pyroxenoid species are present (see mineral composition table, below). Crystals which normalize best to rhodonite contain no Na and ~40.3 wt% Mn (the two elements with the greatest differences among the three minerals) and occur as relict rounded grains within crystals which normalize best to sérandite and contain ~6.0 wt% Na and ~30.2 wt% Mn. A third material contains ~3.0 wt% Na and ~35.2 wt% Mn, and normalizes best to natronambulite after the assumption of ~0.16 wt% Li (again, not verified by ICP-MS or SIMS). Natronambulite is not reported from this locality in the database, and given that the Mn-rich pyroxenoids also show some overlap in optical properties, this identification should be considered tentative pending further study. These pyroxenoids and amphibole(s) occur with abundant quartz and minor braunite. Rare grains of a new Ba-Na-Mn-phosphate with a seemingly merwinite-like formula (end-member: BaNa2Mn2+[PO4]2) were observed during microprobe examination of an original epoxy mount of this rock. Subsequent examination of this thin section (prepared from a different chunk of the same larger specimen) has not yet yielded more of this material. Overall, this thin section would benefit from further study, and the preparation and examination of additional thin sections from the original larger rock would certainly be worthwhile.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-30
(merwinite structure)?
braunite (Mn2+0.94Mn3+0.03Ca0.02Na0.01)Mn3+6.01O8[Si0.98O4]
rhodonite (Mn2+0.73Ca0.29Na0.01)Mn2+1.00Mn2+1.00Mn2+1.00(Mn2+0.90Mn3+0.10)[Si4.95O15]
natronambulite? (Na0.81Li~0.15Ca0.04)(Mn2+0.93Ca0.07)Mn2+1.00Mn2+1.00Mn2+1.00[Si5.00O14](OH)
sérandite (Na0.98Ca0.02)(Mn2+0.98Ca0.02)Mn2+1.00[Si2.99O8](OH)
oxo-amph ss
oxo-amph ss


sample: FKM-31
locality: Mysore district, Karnataka, India.
rock type: corundum-fuchsite schist. Retrogressed (and likely metasomatized) granulite.
major mineralogy: corundum, fuchsite, rutile.
(left: unpolarized light; right: under crossed polars)


sample: FKM-32a (taken from the same slab as FKM-32b)
locality: near Sosnovyy, Karelia Republic, Russia.
rock type: kyanite-staurolite-garnet-fuchsite schist. Amphibolite facies (kyanite zone) metamorphism of gradational metapelite and metaquartzite.
major mineralogy: Abundant porphyroblasts of almandine, chromian staurolite and kyanite in a matrix of chromian muscovite (“fuchsite”), sodic plagioclase (Ab88An12) and quartz, with subordinate Cr-Fe-bearing phlogopite, oxides (ilmenite and rutile [the 0.01 apfu Cr corresponds to ~4597 ppm Cr; also with ~806 ppm Fe]) and apatite.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-32a
rutile (Ti0.99Cr0.01)O2
ilmenite (Fe2+0.95Mn2+0.02Mg0.02)Ti1.01O3
fluorapatite (Ca4.97Mn2+0.01Na0.01)[P3.00O12](F0.93[OH]0.07)
almandine (Fe2+2.20Mg0.39Mn2+0.27Ca0.09Na0.01)(Al1.93Fe3+0.10Cr0.01)[Si2.96Al0.04O12]
kyanite (Al1.98Fe3+0.01Cr0.01)O[Si0.99Al0.01O4]
staurolite 4Al2O[Si0.98Al0.02O4] . (Al0.65Cr0.14Mg0.09Ti0.08Mn2+0.03V0.01)(Fe2+1.59Mg0.31Zn0.020.08)(O2.75[OH]1.25)
muscovite (K0.69Na0.23Ba0.010.07)(Al1.86Mg0.07FeT0.06Ti0.03Cr0.02V0.010.95)[Si3.04Al0.96O10]([OH]1.89O0.07F0.04)
phlogopite (K0.84Na0.050.11)(Mg1.56FeT0.87Al0.38Ti0.06Cr0.03V0.010.09)[Si2.73Al1.27O10]([OH]1.55F0.33O0.12)
“oligoclase” (Na0.88Ca0.15Sr0.01)[Si2.81Al1.19O8]


sample: FKM-32b (taken from the same slab as FKM-32a)
locality: near Sosnovyy, Karelia Republic, Russia.
rock type: fuchsite metaquartzite. Amphibolite facies metamorphism of gradational metapelite and metaquartzite.
major mineralogy: specimen acquired for fuchsite.
(left: unpolarized light; right: under crossed polars)


sample: FKM-33 (billet courtesy of C. Loehn, LSU)
locality: Jayville mine, St. Lawrence Co., NY, USA.
rock type: K-Fe metasomatite associated with Fe-oxide mineralization. The occurrence of metasomatic K-Cl-bearing hastingsite (sensu lato) with magnetite and apatite is characteristic of the ore zone in many IOCG (iron-oxide-Cu-Au) systems (Mazdab, 2003).
major mineralogy: Calcic amphibole is the dominant mineral in this thin section, verified by EPMA as K-F-Cl-bearing hastingsite. This amphibole is similar in composition, and of similar occurrence, to the potassic-magnesio-hastingsite in sample FKM-21. Some magnetite is present, as well as minor quartz and some biotite near Mg/(Mg+∑Fe) ≈ 0.5 and F/(OH+F) ≈ 0.5 in composition. Calcite present in the sample locally contains fine fibrous inclusions of a Fe-rich silicate which normalize best to greenalite, but alternatively could be pyrosmalite-(Fe) or another Fe-rich phyllosilicate.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-33
magnetite Fe2+1.00(Fe3+1.97Al0.01Fe2+0.01)O4
hastingsite (Na0.42K0.390.19)(Ca1.81Na0.19)(Fe2+2.63Mg1.19Fe3+1.01Al0.08Mn2+0.06Ti0.03Zn0.01)
greenalite? (Ca0.07K0.01Na0.01)(FeT4.64Mg0.47Al0.12MnT0.110.66)[Si4.00O10]([OH]7.85Cl0.15)
trioct mica ss
trioct mica ss


sample: FKM-34
locality: Nordfjord, Sogn og Fjordane, Norway.
rock type: garnet-omphacite eclogite. Eclogite facies metamorphosed mafic volcanic, likely Na-metasomatized (spillitization) prior to high-P metamorphism. Compare this to sample FKM-97, which is presumably also a garnet eclogite, but probably started out as a much different protolith.
major mineralogy: Classic mafic eclogite assemblage of predominately garnet (from Ca-Mg-rich almandine to Fe-Ca-rich pyrope) and slightly zoned omphacite. Minor kyanite, zoisite and paragonite, and rare barroisite to taramite NaCa-amphibole ss (more abundant in garnet) and magnesio-hornblende (more abundant in omphacite) are present. Accessory rutile (also with ~130 ppm Cr), fluorapatite to hydroxylapatite apatite ss, zircon, chalcopyrite and Co-pentlandite are also present.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-34
rutile (Ti0.99Fe3+0.01)O2
fluorapatite-rich apatite ss Ca4.97[P3.02O12](F0.65[OH]0.35)
hydroxylapatite-rich apatite ss (Ca4.94Na0.01)[P3.04O12]([OH]0.71F0.29)
almandine-rich garnet ss (Fe2+1.41Ca0.76Mg0.70Mn2+0.12Na0.01)(Al1.89Fe3+0.11)[Si3.00O12]
pyrope-rich garnet ss (most Ca-rich) (Mg1.15Fe2+1.09Ca0.70Mn2+0.05)(Al1.91Fe3+0.08)[Si3.00O12]
pyrope-rich garnet ss (most Mg-rich) (Mg1.39Fe2+1.09Ca0.49Mn2+0.02)(Al1.91Fe3+0.09)[Si3.00O12]
kyanite Al1.99O[Si0.99Al0.01O4]
zoisite Ca0.99Ca0.97Al1.02Al1.00(Al0.88Fe3+0.11)O[Si1.98Al0.02O7][Si0.99Al0.01O4](OH)
omphacite (main; most Na-Al-rich) (Ca0.63Na0.35Mg0.02)(Mg0.58Al0.35Fe2+0.03Fe3+0.03)[Si1.96Al0.04O6]
omphacite (patchy; most Ca-Mg-rich) (Ca0.76Na0.20Mg0.04)(Mg0.65Al0.27Fe2+0.08)[Si1.95Al0.05O6]
magnesio-hornblende (Na0.18K0.040.78)(Ca1.53Na0.47)(Mg3.88Al0.66Fe3+0.23Fe2+0.20Ti0.02Ni0.01)
barroisite-rich NaCa-amph ss (Na0.26K0.050.69)(Ca1.38Na0.62)(Mg3.15Al0.90Fe3+0.69Fe2+0.21Ti0.04Mn2+0.01)
barroisite (Hawthorne et al., 2012)
or ~[barroisite]-[taramite] join
(Leake et al., 1997) -rich NaCa-amph ss
taramite-rich NaCa-amph ss (Na0.57K0.010.42)(Ca1.40Na0.60)(Mg1.76Al1.09Fe2+1.01Fe3+1.00Ti0.08Mn2+0.04Ni0.01)
paragonite (Na0.91Ca0.04K0.010.04)(Al1.99FeT0.03Mg0.010.97)[Si2.93Al1.07O10]([OH]1.99O0.01)


sample: FKM-35
locality: unlabeled, but believed to be from the Bancroft area, Hastings Co., Ontario, Canada.
rock type: altered(?) nepheline-sodalite syenite, or possibly a nepheline-sodalite fenite?
major mineralogy: test.
(left: unpolarized light; right: under crossed polars)


sample: FKM-36
locality: unlabeled, but believed to be from the Franklin marble, in the general region of Sussex Co., NJ across to Orange Co., NY, USA.
rock type: spinel-chondrodite marble. Granulite facies meta-siliceous dolostone.
major mineralogy: Chondrodite with minor spinel in a coarse carbonate (calcite > dolomite). Sample FKM-8 is another chondrodite-bearing marble (also containing the additional humite group mineral norbergite) from the Franklin district. See the discussion under sample FKM-8 for details about the normalization scheme used for the humite group minerals and the rationale for estimating possible boron. Samples FKM-184, from a Franklin marble exposure in Edenville, NY, and FKM-112, also believed to be from the Franklin area, both contain yet another humite group species: clinohumite.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-36
spinel (analysis pending)
chondrodite (Mg3.88Fe3+0.08Fe3+0.02Ti0.01)[Si1.90B0.10O7.91(OH)0.09](F1.27[OH]0.73O0.01)


sample: FKM-37
locality: unlabeled, but believed to be from the Franklin marble, in the general region of Sussex Co., NJ across to Orange Co., NY, USA.
rock type: high grade borate-bearing marble. Granulite facies meta-siliceous dolostone (boron and fluorine may be of metasomatic origin?)
major mineralogy: specimen acquired for fluoborite.
(left: unpolarized light; right: under crossed polars)


sample: FKM-38
locality: Cascade Slide, Cascade Mtn., Keene, Essex Co., NY, USA.
rock type: high grade diopside-bearing marble xenolith. Upper granulite facies metamorphosed siliceous limestone/dolostone.
major mineralogy: Abundant gemmy rounded diopside grains, with minor Al-bearing andradite and REE-bearing vesuvianite, in calcite. The vesuvianite was analyzed with the petroEPIDOTE analytical routine and normalized to 68[O] + 1[O] + 9[OH+F+Cl], with all Fe treated as Fe3+ and all Mn treated as Mn2+. The B values in the vesuvianite are an assumption and are not based on direct measurement; however, enough estimated B was added to each analysis so that the normalization would de-populate excess Si+Al from the nominally vacant B site. These additions also improved the overall analytical totals, and would be consistent with both the ability of vesuvianite to contain B, and the occurrence of harkerite in the assemblage. Scattered but tiny examples of an unknown Pb-Fe-Mn-Zn mineral (possibly a magnetoplumbite group mineral?; see below for a ∑cation = 26 normalization) and an unknown Ca-Fe-silicate (total = 90.2 wt%) occur in fractures and require further study. Tiny Fe sulfide (too small to analyze) is also present.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-38
(magnetoplumbite group?)
calcite Ca0.99[CO3]
andradite (Ca2.96Mg0.01Fe2+0.01Mn2+0.01Y0.01)(Fe3+1.38Al0.57Ti0.03Mg0.02)[Si2.99Al0.01O12]
(most REE-rich)
(less REE-rich)
diopside Ca0.99(Mg0.88Fe3+0.05Al0.03Fe2+0.03)[Si1.91Al0.09O6]


sample: FKM-39 (separate specimen from sample FKM-39b)
locality: Murunskii massif, Chara River region, Sakha Republic, Russia.
rock type: Charoite schist; a K-rich metasomatite formed as part of a “charoitite-carbonatite” complex (Mitchell and Vladykin, 1996), this rock might be considered a type of K-fenite?
major mineralogy: Predominately charoite, zoned amphibole (cores of fluorian potassic-richterite grading outward to rims of fluorian potassic-magnesio-arfvedsonite), quartz, microcline, and minor aegirine (with up to 1140 ppm V). Sample FKM-39b is another charoite-bearing rock from the same general locality, although the charoite composition and the overall mineralogy differ slightly from this sample.
(left: unpolarized light; right: under crossed polars)


sample: FKM-39b (separate specimen from sample FKM-39)
locality: Murunskii massif, Chara River region, Sakha Republic, Russia.
rock type: tinaksite-charoite-microcline schist; a K-rich metasomatite formed as part of a “charoitite-carbonatite” complex (Mitchell and Vladykin, 1996), this rock might be considered a type of K-fenite?
major mineralogy: Charoite, Fe-rich microcline and quartz are the dominant minerals in the sample, with additional abundant tinaksite blades and scattered V-bearing aegirine. Although conspicuous by optical microscopy, the aegirine is essentially indistinguishable from the charoite with BSE imaging due to similar average z. The microcline is zoned from 0.07 apfu Fe3+ in the core to 0.14 apfu Fe3+ in the rim. Although dispersion in microcline is generally reported as weak r > v, the microcline in this sample shows extreme v > r dispersion; indeed, the dispersion is so strong that under crossed polars the crystals show an atypical marked blue to brown anomalous birefringence. Another unusual feature of the microcline is that under the electron beam it shows an initial strong red cathodoluminescence that gradually becomes blue. As for the charoite, the normalization was done to ∑T = 70 (including Fe3+), based on the updated structural formula determined by Rozhdestvenskaya et al. in their 2010 [← subscription required] and 2011 papers. The 180[O] was reduced by sufficient [OH] to charge balance the formula, assigning all Fe as Fe3+ and assuming Mn3+/∑Mn = ~0.1; Mn3+ appears to be responsible for the lilac to violet color (Evdokimov et al., 2000; referenced in Rozhdestvenskaya et al., 2010). Additional H2O in the channels is estimated to give a yield a cumulative (all OH + H2O) charoite molar H2O content of ~16. Although this H2O estimate still leaves the analytical total a bit low (at ~98.8 wt%), the calculated H2O wt% is roughly 4.6 wt% which is consistent with the reported water values (one by DTA) referenced in the Handbook of Mineralogy’s charoite entry. The charoite is also strongly cathodoluminescent in blue. Minor minerals present include one spray of dalyite needles associated with some of the aegirine, abundant tiny wide-scattered inclusions of galena (particularly in the charoite), and some localized unidentified alteration of the charoite. Sample FKM-39 is another charoite-bearing rock from the same general locality, although the charoite composition and the overall mineralogy differ slightly from this sample.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-39b
tinaksite (K1.96Na0.01Sr0.01Ba0.01)(Na0.92Ca0.08)(Ca1.83Fe3+0.06Mg0.05Mn2+0.05V0.01)Ti1.01O1.00
aegirine (most Na+Fe-rich) (Na0.91Ca0.08)(Fe3+0.84Mg0.09Ti0.04Fe2+0.03)[Si2.00O6]
aegirine (most V-rich) (Na0.84Ca0.15Mg0.01)(Fe3+0.74Mg0.13V0.07Fe2+0.04Ti0.02)[Si1.99Fe3+0.01O6]
charoite (K14.59Ba1.35Sr0.53Mn2+~0.16)(Ca27.02Na4.64Sr0.25Zr0.04Mn3+~0.02Ti0.01)
[Si69.90Fe3+~0.04S0.04P0.02Al0.01O~174.21(OH)~5.79](F3.28[OH]0.70Cl0.02) . ~12.75H2O
dalyite (K1.84Ca0.13Fe2+0.02Ba0.01)(Zr0.77Ti0.21Hf~0.01Sn0.01)[Si5.91Ti0.06O14.99F0.01]
microcline (core) (K0.99Na0.01Mg0.01)[Si2.99Al0.94Fe3+0.07O8]
microcline (rim; most Fe-rich) (K0.99Mg0.01)[Si3.00Al0.85Fe3+0.14O8]


sample: FKM-40
locality: Antanimora commune, Ambovombe district, Tuléar province, Madagascar.
rock type: high grade spinel-bearing marble, with a seemingly metasomatic contribution.
major mineralogy: Abundant spinel in calcite (relict dolomite is also present), with scattered patchy-zoned apatite ranging in composition from Cl-rich fluorapatite to essentially end-member chlorapatite. Minor quartz and small quantities of an ill-identified alteration phyllosilicate (possibly a Ca-dominant, Li-bearing tosudite; this normalizes extremely well) are present. One tiny, partially altered forsterite was also identified. Small thorianite inclusions are present in the apatite.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-40
spinel (Mg0.86Fe2+0.13)Al2.01O4
apatite ss
apatite ss
“Ca-dominant tosudite”? (Ca0.33K0.04Na0.03Ba0.03)(Al4.27Mg0.97FeT0.41Zn0.01Li~0.34)[Si7.17Al0.82P0.01S0.01O18](OH)12 . 5H2O


sample: FKM-41
locality: Oka complex, Oka, Laurentides, Québec, Canada. This sample is similar to FKM-55, also from Oka, but is very similar but is richer in silicates and pyrochlore.
rock type: carbonatite (sovite).
major mineralogy: This sample is one of the typical pyrochlore-bearing assemblages mined at Oka for niobium. The pyrochlore in this sample consists of large deep chocolate-brown octahedra (in hand sample) in a matrix of predominately calcite, diopside and fluorapatite, along with subordinate magnetite and phlogopite. Sparse tiny barite is also present. There is some variation in the pyrochlore chemistry, visible both optically and in BSE imaging, as other researchers have also noted (Petruk & Owens, 1975). As with several of the complex HFSE minerals, normalization of pyrochlore-group minerals can be challenging owing to potential vacancies in the large “A” cation site and also the two anion sites, as well the possibility of structural H2O distributed over multiple sites (Atencio et al., 2010). Adsorbed H2O is also possible, particularly in increasingly metamict samples. As recommended in the previous references, the normalization routine used here was ∑”B”-site = 2. A number of additional simplifying assumptions were also included. Ta was not measured in this analytical set, and presumably relatively low Ta was estimated for the different Oka pyrochlore compositional variants from the data of Petruk & Owens, 1975. All Fe was treated as Fe3+. The “X” and “Y” anion sites were assumed to be fully occupied by F, OH and O (the ratio of the latter two calculated by overall charge balance). Where the analytical total was <100 wt%, H2O was added to fill any “A”-site vacancy until either the vacancy was filled or the overall total hit 100 wt%. Lastly, in each analysis, the “X” anion site was preferentially filled with O (up to the maximum site occupancy of 6.00 apfu), and the “Y” anion site was preferentially filled with F (up to the maximum site occupancy 1.00 apfu), before OH and any leftover O were distributed into the remaining available space of the two sites. One result of this filling sequence is that while the most F-rich composition had 0.49 apfu F in the “Y”-site, even that analysis normalized to a hydroxy-“pyrochlore” species (due to 0.51 apfu OH). Note that had even only 0.03 apfu OH been moved into the “X”-site (with a corresponding amount of O moved into the “Y”-site), the analysis would have normalized to a fluor-“pyrochlore” species; hence, because the actual distribution of O and OH (and also unaccounted vacancies and H2O) between the two anion sites are not known for this material, the name in the composition table are followed by a (?); this possibility also holds true for the other relatively F-rich analysis, but not for the latter two more F-poor analyses. In addition to the zoning in the pyrochlore, the diopside in this sample is also slightly compositionally zoned, and this too can be observed in the scanned image. There is also mild compositional zoning in the phlogopite. Unlike the pyrochlore and diopside, this zoning is not readily visible in the scanned image, although it is quite distinctive using a petrographic microscope; also, under the microscope the phlogopite in this thin section shows anomalous pleochroism, where the strongest absorption (deeper color) occurs when the cleavage is perpendicular to the vibration direction of the lower polarizer. This is atypical because in most phlogopite and in all more Fe-rich biotite the strongest absorption is when the cleavage is parallel to the lower polarizer.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-41
magnetite (Fe2+0.75Mn2+0.19Mg0.05Zn0.01)(Fe3+1.71Fe2+0.12Ti0.12Al0.04V0.01)O4
(main z)
(weakly higher z rim)
(small unzoned)
(small unzoned in magnetite)
calcite (Ca0.97Mg0.01Mn2+0.01Sr0.01)[CO3]
fluorapatite (Ca4.87Na0.04Sr0.02Ce0.02Nd0.01La0.01)[P2.96Si0.04O12](F0.54[OH]0.46)
diopside (main z) (Ca0.96Na0.04)(Mg0.74Fe2+0.12Fe3+0.06Mn2+0.05Al0.01Ti0.01)[Si1.93Al0.07O6]
diopside (patchy lower z) (Ca0.98Na0.02)(Mg0.85Fe2+0.09Mn2+0.04Fe3+0.01Al0.01)[Si1.98Al0.02O6]
phlogopite (main z) (K0.89Na0.05Ba0.020.04)(Mg2.24FeT0.55MnT0.08Al0.06Ti0.06Nb0.01)[Si2.85Al1.15O10]([OH]1.78O0.13F0.09)
(weakly higher z rim)


sample: FKM-42
locality: Martiniana Po, Dora Maira massif, Cuneo province, Piemonte, Italy.
rock type: pyrope-kyanite-talc schist (“whiteschist”). UHP eclogite facies sepiolitic(?) metapelite with accompanying metasomatism?
major mineralogy: Large shattered near end-member pyrope with quartz (presumably coesite at peak P), kyanite, minor rutile (also with ~1686-~2710 ppm Fe, ~204 ppm Cr and ~112 ppm Mn), phengitic white mica along the muscovite-aluminoceladonite join, and abundant talc. The garnets at this locality are notable, having so little Fe that they’re almost white in color, and growing to the size of a grapefruit (perhaps even larger!) Relict coesite may occur armored in some intact garnet (although not observed in this thin section). Small zircon and monazite crystals are scattered in the sample. This sample is from the same general vicinity as FKM-258, but differs somewhat in mineralogy.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-42
rutile (Ti0.98Al0.01)O2
pyrope (Mg2.87Fe2+0.11Ca0.01Na0.01)(Al1.97Fe3+0.03)[Si2.95Al0.05O12]
kyanite Al2.00O[Si0.99Al0.01O4]
talc Na0.01(Mg2.87Al0.03FeT0.010.09)[Si4.03O10]([OH]1.89F0.10Cl0.01)
[muscovite]-[aluminoceladonite] join


sample: FKM-43 (self-collected in June 1996)
locality: Pasminco North mine, Broken Hill, Yancowinna Co., NSW, Australia.
rock type: sphalerite-tephroite marble. Granulite facies Zn-Mn calcareous volcanogenic exhalite?
major mineralogy: Abundant tephroite and sphalerite (with ~1590 ppm Cd), with minor galena (with ~440 ppm Sb), chalcopyrite (with ~790 ppm Sn) and apatite, in calcite.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-43
galena Pb1.00S1.00
sphalerite (Zn0.76Fe2+0.16Mn2+0.07)S1.00
chalcopyrite Cu0.98Fe1.01S2.01
calcite (Ca0.95Mn2+0.05)[CO3]
fluorapatite (Ca4.99Mn2+0.02Y0.02)[P2.89Si0.05As5+0.01O12](F0.84[OH]0.15Cl0.01)
tephroite (Mn2+0.98Ca0.02)(Mn2+0.49Fe2+0.45Mg0.03Fe3+0.03)[Si0.97Fe3+0.03O4]


sample: FKM-44
locality: Imilchil, Er Rachidia province, Meknès-Tafilalet region, Morocco.
rock type: greenschist facies Ca-(Na) alteration assemblage associated with Fe-oxide mineralization. This is one of the typical hydrothermal mineral assemblages characteristic of IOCG (iron-oxide-Cu-Au) systems, although the more Na+Ti-rich amphiboles here are atypical for this assemblage and likely represent a different higher-T event.
major mineralogy: Epidote, titanite (some with abundant tiny ilmenite inclusions), complexly-zoned calcic amphibole ranging from ferro-actinolite and actinolite to more Na+Ti-rich compositions (see composition table), clinochlore and quartz are all abundant. In places the epidote and titanite grow as large euhedral crystals into open-space that is now variably-filled in with quartz. Minor diopside is intimately intergrown with the amphibole and may represent a relict (pre-metasomatic) phase. An additional table with data for the REE and trace element chemistry for the Imilchil titanite follows the main mineral composition table; these are illustrated relative to other titanite compositions in Mazdab et al., 2009.
*Note: for classification purposes, the choice of edenite rather than ferri-sadanagaite as a join end-member (see composition table) assumes that VITi occurs at M1 and does not contribute a “2Ti” component to the Hawthorne et al., 2012 VI(Al+Fe3++2Ti) calculation. This assumption seems reasonable, because while a variety of other linear combinations can reproduce the Na, Ca, Mg, Ti, VI(Fe3++Al) and W[O]calc proportions observed in the Imilchil Na+Ti-rich amphiboles (e.g. [ferri-kaersutite]-[magnesio-hastingsite] or [ferri-kaersutite]-[ferri-sadanagaite]), only the linear combination [edenite]-[ferri-kaersutite] can also simultaneously yield an average Si apfu greater than 6.5 (i.e. Si = 6.65 apfu is observed for one sample, and no sample shows Si apfu < 6). The two end-members of the join are related by the exchange vector [VI(TiFe3+)IVAl]1[VI(Mg2)IVSi(H2)]-1.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-44
ilmenite (Fe2+0.69Mg0.15Fe3+0.14Mn2+0.01Ca0.01)(Ti0.86Fe3+0.13V0.01)O3
titanite (core; most REE+Zr-rich) (Ca0.97Na0.01Ce0.01Y0.01)(Ti0.85Zr0.07Fe3+0.04Nb0.02V0.01)(O0.94[OH]0.06)[Si0.97Al0.02Fe3+0.01O4]
titanite (main; most Ca+Ti-rich) Ca1.01(Ti0.98V0.01)(O0.93[OH]0.06F0.01)[Si0.95Al0.03Fe3+0.01O4]
epidote (center; most Al-rich) Ca0.98(Ca0.96Sr0.04)Al1.01Al1.00
epidote (outer; most Fe-rich) Ca1.00(Ca0.98Sr0.02)Al0.99Al1.00Fe3+0.99O1.00[Si1.96Al0.04O7][Si0.98Al0.02O4](OH)
diopside (Ca0.93Na0.05Mg0.02)(Mg0.83Fe2+0.09Fe3+0.07Ti0.01)[Si1.95Al0.04Fe3+0.01O6]
ferro-actinolite-rich Ca-amph ss (Na0.010.99)Ca2.00(Fe2+2.58Mg2.29Mn2+0.07Fe3+0.05)
actinolite-rich Ca-amph ss
(most Mg-rich)
~[ferri-kaersutite]-[edenite]* join-rich
oxo/Ca-amph ss (most Mg+Si-rich)
~[ferri-kaersutite]-[edenite]* join-rich
oxo/Ca-amph ss (most Ti+Al-rich)
~[ferri-kaersutite]-[edenite]* join-rich
oxo/Ca-amph ss (most Na+Fe-rich)
clinochlore (most Mg-rich) (Mg2.69FeT1.67Al1.36MnT0.030.25)[Si2.79Al1.21O10](OH)8.00
clinochlore (most Fe-rich) (Mg2.29FeT1.99Al1.29MnT0.020.41)[Si2.61Al1.39O10](OH)8.00

The following titanite trace element analyses are SHRIMP-RG data collected at the U.S.G.S.-Stanford Ion Microprobe Laboratory on epoxy-mounted grain separates measured against the BLR-1 titanite standard (Mazdab et al., 2009… the more detailed Pb concentrations presented here correct an erroneous value for [Pb]total that appears in Mazdab, 2009). A note on significant figures: owing to the challenges of conveying observable and sometimes surprisingly reproducible variations in elements that might span 3 or more orders of magnitude between samples, I may be a bit inconsistent here. There may be some cases when less significant figures may be warranted, but where otherwise recognizable precision is suggested by the larger sample set and I wanted to convey this greater reproducibility; in other cases, too many significant figures might just be wishful thinking on my part (and those should get fixed here eventually). An added complication is the limitation of differentiating true measurement reproducibility with any subtle heterogeneity in the standard.

grain 5;
highest z zone
grain 5;
mod-high z zone
grain 5;
moderate z zone
grain 5;
mod-low z zone
nominal BLR-1
Li 0.3 0.2 0.1 <0.1 6.5
Be not analyzed not analyzed not analyzed not analyzed ~0.15
B 0.5 0.8 1.1 0.7 8.4
F 936 571 646 327 21800
Na 667 553 567 312 1400
Mg 233 199 215 222 650.
Al 2570 2430 3160 3670 16300
P 756 509 361 393 65
Cl 5 7 9 7 10.
K 1.4 1.2 1.3 1.0 2.5
Ca ~220000 ~209000 ~228000 ~190000 193800
Sc 2.1 1.8 1.6 1.3 2.8
Ti ~241000 ~233000 ~246000 ~225000 197900
V 346 290. 345 217 110
Cr 0.7 0.6 1.1 2.3 105
Mn 305 267 270. 171 1000
Fe 11600 10300 12600 8300 19100
Co 0.2 0.2 0.2 0.1 0.3
Ni 0.7 0.9 0.7 0.6 0.7
Cu 2.2 2.1 2.8 1.9 2.1
Zn 16 11 21 15 50.
Ga 2.7 1.5 1.8 2.0 6.1
Ge 2.2 2.8 2.5 2.7 3.7
Sr 52 45 43 31 50.
Y 642 442 376 176 3400
Zr 11000 11100 6520 765 1300
Nb 1940 1080 557 265 3650
Sn 48 38 30 21 262
Sb not analyzed not analyzed not analyzed not analyzed ~0.5
Cs not analyzed not analyzed not analyzed not analyzed ~0.6
Ba 174 166 191 130 ~0.2
La 722 436 331 357 375
Ce 1490 898 661 745 1660
Pr 162 95 75 76 285
Nd 701 428 349 310 1490
Sm 170 111 99 61 500
Eu 38 24 18 15 74.2
Gd 188 123 121 54 655
Tb 27 18 18 7.3 122
Dy 152 98 93 36 820.
Ho 30 19 17 6.8 187
Er 70 45 39 18 525
Tm 9.3 5.4 4.8 1.8 71.5
Yb 54 34 29 11 350.
Lu 6.3 3.9 2.8 1.1 35
Hf 193 191 103 6.2 52.5
Ta 228 136 70. 15 225
W not analyzed not analyzed not analyzed not analyzed ~2.3
204Pb not analyzed not analyzed not analyzed not analyzed ~0.038
206Pb 0.37 0.08 0.15 0.12 ~46
207Pb not analyzed not analyzed not analyzed not analyzed ~3.9
208Pb 0.28 0.12 0.21 0.10 ~9.6
Bi not analyzed not analyzed not analyzed not analyzed ~6
Th 134 57 44 17 186
U 44 16 11 7.5 300.


sample: FKM-45 (billet from Univ. Arizona economic geology collection)
locality: Franklin mining district, Sussex Co., NJ, USA.
rock type: biotite-clinopyroxene-dominant calc-silicate rock. A skarn-like granulite facies Zn-Mn-rich volcanogenic exhalite(?), likely affected by subsequent metasomatism.
major mineralogy: Unlike most of the other Franklin area samples in this collection, this specimen is primarily massive silicate with subordinate oxide and little carbonate. Zn- and Mn-rich clinopyroxene, compositionally roughly along the diopside-augite nomenclature boundary (with respect to Ca content), is the dominant mineral present. This cpx consists of a slightly lower Z diopside making up the bulk of the material, and patchy areas of a slightly higher Z (due to increased Mn) augite scattered within. In the Franklin area, this fairly abundant Zn- and Mn-rich cpx is known as “jeffersonite” (see Frondel and Ito, 1966). Widespread in the cpx are small abundant inclusions of rhodonite, suggesting the cpx may have replaced it. Rhodonite also occurs as thicker bands, locally between cpx and mica. The mica was originally thought to be hendricksite, but analytical results indicate Mg>Zn, so it is in fact a Zn- and Mn-rich phlogopite. Minor amounts of two amphibole varieties are observed. An unusual Zn- and Mn-bearing hastingsite locally occurs between cpx and mica (similar in occurrence to the thicker rhodonite bands), and a comparably Zn- and Mn-enriched tremolite occurs as alteration stringers within the cpx. Franklinite and orange gahnite (as discrete grains, and as inclusions and overgrowths associated with the other; see FKM-48) are the dominant oxide minerals present, although a zincian pyrophanite also occurs as overgrowns on some of the franklinite. Scattered areas of Mn-bearing calcite occur throughout the sample, and as well as small inclusions within the cpx and rhodonite. Thin, enlongate stringers of willemite (bright green CL) occur in fractures in the gahnite and occasionally between the cleavages of the mica. Minor tiny ZnS (low-Fe but Cd-rich, by EDS; bright blue CL) and rare tiny galena are scattered in the sample.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-45
pyrophanite (Mn2+0.90Fe2+0.06Zn0.03Fe3+0.01)Ti0.99O3
gahnite (Zn0.89Fe2+0.08Mn2+0.02Mg0.01)(Al1.87Fe3+0.12)O4
franklinite (Zn0.80Mn2+0.19Mg0.01)(Fe3+1.52Al0.09Mn2+0.17Ti0.19Fe2+0.02)O4
calcite (Ca0.90Mn2+0.08Sr0.01)[CO3]
diopside-rich cpx ss
(“jeffersonite”; main)
augite-rich cpx ss
(“jeffersonite”; patchy)
rhodonite (coarse bands) (Ca0.89Mn2+0.11)Mn2+1.00Mn2+1.00Mn2+1.00(Zn0.37Mg0.26Mn2+0.25Mn3+0.08Fe3+0.03)[Si4.87Fe3+0.12O15]
(inclusions in cpx)
tremolite (Na0.18K0.020.80)(Ca1.27Na0.41Mn2+0.32)(Mg3.30Zn0.57Fe2+0.52Mn2+0.37Fe3+0.23)
hastingsite (Na0.87K0.12)(Ca1.53Na0.35Mn2+0.11)(Mg2.49Mn2+0.79Zn0.68Fe3+0.62Fe2+0.25Al0.10Ti0.06)
phlogopite (most Zn-rich) (K0.83Ba0.07Na0.050.05)(Mg1.72Zn0.58FeT0.31MnT0.27Ti0.050.07)[Si2.78Al1.22O10]([OH]1.51F0.39O0.09Cl0.01)


sample: FKM-46 (billet courtesy of J. Aleinikoff, U.S.G.S.-Denver; sample MR-99-12)
locality: Moose River, Lyonsdale, Lewis Co., NY, USA.
rock type: almandine-prismatine-cordierite gneiss. Granulite facies B-bearing metapelite.
major mineralogy: Porphyroblasts of prismatine, almandine(?) and cordierite (the latter partially altered to “pinite” [chlorite + muscovite]), with scattered biotite, tourmaline, minor rutile and minor hercynite, with quartz, K-feldspar and plagioclase. For comparison, other prismatine-bearing (and kornerupine-bearing) samples featured here include FKM-59 and FKM-67.
(left: unpolarized light; right: under crossed polars)


Franklin New Jersey willemite ore in thin section under UV light

sample: FKM-47
locality: Franklin mining district, Sussex Co., NJ, USA.
rock type: test.
major mineralogy: specimen acquired for willemite.
(upper left: unpolarized light; upper right: under crossed polars; lower: under shortwave ultraviolet [SWUV] light)


Franklin New Jersey willemite ore in thin section under UV light

sample: FKM-48
locality: Franklin mining district, Sussex Co., NJ, USA.
rock type: gahnite-franklinite-tephroite-willemite marble. Granulite facies Zn-Mn calcareous volcanogenic exhalite?
major mineralogy: The specimen is a coarse-grained marble made up of Mn-rich calcite. The predominant porphyroblasts are willemite (the abundant colorless moderate relief crystals that slightly stand out from the calcite matrix), a Mg-rich Mn-olivine (the higher relief “highly-shattered” very pale gray crystals), franklinite (opaque) and gahnite* (pale to bright orange-yellow; see FKM-45). Within some of the gahnite is minor Ca-rich rhodochrosite, and some of the gahnite also shows overgrowths of franklinite. Scattered tiny barite (too small to accurately analyze) is also present. The Mg-Mn-olivine has overall Mn>Mg and so is ostensibly tephroite. However, site occupancy measurements on Mg-Mn-olivine by Francis and Ribbe, 1980 (including on a Zn-bearing Franklin sample similar to the one presented here) demonstrate significant ordering of Mn2+ into the slightly larger M2 site. Hence, with Mg predicted to be more abundant than Mn in the M1 site in this sample, it is likely this olivine more closely resembles an ordered M2MnM1Mg[SiO4] hypothetical end-member than a disordered Mg-bearing tephroite, M2(Mn,Mg)M1(Mn,Mg)[SiO4].
*Note: prior to examining this thin section on the microprobe, the yellow gahnite in this sample was originally thought to be andradite garnet, and is misidentified as such in Isotropic Minerals in Thin Section; I regret the error, and offer a correction here. Because only a limited number of optical tests are available to characterize isotropic minerals in thin section (i.e. color, relief [relative refractive index], cleavage [if present], habit and paragenesis], these minerals can in some cases be the among the most challenging to differentiate.
(upper left: unpolarized light; upper right: under crossed polars; lower: under shortwave ultraviolet [SWUV] light)

mineral representative mineral compositions in FKM-48
gahnite (most Fe-rich) (Zn0.90Fe2+0.04Mn2+0.04Mg0.02)(Al1.76Fe3+0.24)O4
gahnite (most Al-rich) (Zn0.92Fe2+0.06Mn2+0.01Mg0.01)(Al1.91Fe3+0.09)O4
franklinite (Zn0.80Mn2+0.13Mg0.04Fe2+0.03)(Fe3+1.56Al0.18Mn2+0.13Ti0.13)O4
calcite (bulk) (Ca0.85Mn2+0.12Mg0.02Sr0.01)[CO3]
rhodochrosite (inclusions in gahnite) (Mn2+0.81Ca0.18Mg0.01)[CO3]
willemite (Zn0.67Mn2+0.17Mg0.15)Zn0.99[Si1.00O4]
“MnMg[SiO4]” olivine (historically tephroite) Mn2+1.00(Mg0.61Zn0.22Mn2+0.15Mn3+0.03)[Si0.97Fe3+0.03O4]


sample: FKM-49 (billet from Univ. Arizona economic geology collection, J. Hamblock thesis collection)
locality: San Carlos intrusive complex, Tamaulipas, Mexico.
rock type: nepheline syenite.
major mineralogy: Amphibole (ferri-kaersutite grading to and/or overgrown with magnesio-hastingsite), scattered large titanite crystals (to ~1 cm, in the hand sample), nepheline, orthoclase, and plagioclase.
(left: unpolarized light; right: under crossed polars)


sample: FKM-50
locality: Lovozero massif, Kola Peninsula, Murmanskaja Oblast’, Russia.
rock type: test.
major mineralogy: specimen acquired for murmanite.
(left: unpolarized light; right: under crossed polars)


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