samples FKM-151 to FKM-175


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-151
locality: Øvstebø, Kleppan, Sauland, Hjartdal, Telemark, Norway.
rock type: test.
major mineralogy: specimen acquire for Cu-bearing vesuvianite (“cyprine”).
(left: unpolarized light; right: under crossed polars)


sample: FKM-152
locality: Durham Ranch, near Wright, Campbell Co., WY, USA.
rock type: paralava.
major mineralogy: Ferro-indialite (the high-T hexagonal dimorph of sekaninaite) reported, but not observed in this thin section. In fact, no recognizable minerals were observed in the dark essentially glassy matrix of this sample.
(left: unpolarized light; right: under crossed polars)


sample: FKM-153
locality: Nusfjord, Flakstadøya, Lofoten, Nordland, Norway.
rock type: test.
major mineralogy: reported as potassic-chloro-ferro-sadanagaite, but no amphibole present in this thin section.
(left: unpolarized light; right: under crossed polars)


sample: FKM-154
locality: New Amianthus mine, Kaapsche, Barberton, Mpumalanga province, South Africa.
rock type: pervasively altered chromitite or similar chromite-rich ultramafic rock.
major mineralogy: Massive stichtite (of undetermined polytype) veined with chrysotile, with sparse scattered tiny chromite.
(left: unpolarized light; right: under crossed polars)


sample: FKM-155
locality: “evaporite occurrence”, Sar-e-Sang, Koksha valley, Badakhshan province, Afghanistan.
rock type: Scapolite-bearing gypsum rock. Retrogressed high-grade(?) meta-evaporite.
major mineralogy: Sample consists of large abundant porphyroblasts of gemmy transparent purple (in hand sample) marialite in a groundmass of fine-grained gypsum (anhydrite at peak metamorphic conditions?). Scattered crystals of presumably authigenic albite (untwinned) and K-spar (also untwinned… orthoclase?) are present, both as small isolated masses within the gypsum, and in the case of the K-spar, as somewhat larger aggregates partially rimming some of the scapolite crystals. Extremely tiny crystal clusters of celestite (too small to analyze accurately) are abundantly scattered in the gypsum matrix. Very rare tiny crystals of fluorapatite, monazite-(Ce) and allanite-(Ce) (also all too small to analyze) also occur within the gypsum matrix. These latter accessory minerals are presumably detrital, and are believed so in part due to their size, scarcity and chemistry (i.e. an authigenic REE-bearing epidote-group mineral in this environment would seem more likely to be a dollasite [perhaps one Cl-rich and Ce-poor] rather than an allanite). Sample FKM-25, also from Sar-e-Sang, may represent a carbonate-dominated facies depositionally-related to the evaporite facies represented by this sample. Note: The billet was polished for analysis in order to preserve the integrity of the thin section (the gypsum in the thin section would likely have been severely damaged during removal of the carbon coat). One consequence of hand polishing the billet is that some of the smaller hard minerals developed extreme polishing relief; possible curvature of some of these sample surfaces may be reflected in part in the sub-ideal feldspar stoichiometries and also in the inability to analyze the smaller detrital phases.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-155
albite (isolated in gypsum) (Na0.99Ca0.01K0.01)[Si2.98Al1.02O8]
orthoclase (isolated in gypsum) (K0.88Na0.06Ba0.01)[Si2.97Al1.03O7.99Cl0.01]
orthoclase (adjacent to marialite) (K0.93Na0.03)[Si2.98Al1.02O8]
marialite (Na2.39Ca0.33K0.27Sr0.01)[Si8.64Al3.36Fe3+0.01O24] . (Na1.02Ca0.04)(Cl0.98[CO3]0.05[SO4]0.01)


sample: FKM-156
locality: Malyshevo mine, near Ekaterinburg, Sverdlovskaya Oblast’ (middle Ural Mtns. region), Russia.
rock type: chrysoberyl-chlorite-biotite schist. This schist likely has a significant metasomatic component.
major mineralogy: Chrysoberyl porphyroblasts in a matrix of clinochlore and fluorian phlogopite. In BSE imaging, the chrysoberyl shows irregular higher “z” patches that appear to be mildly-enriched in Sn (up to 0.76 wt% Sn). It is uncertain if this Sn is actually in solid solution, or is present as dispersed sub-micron “invisible” cassiterite. For comparison, another chrysoberyl-bearing sample featured here is FKM-16.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-156
chrysoberyl (higher “z” zones) (Al1.94FeT0.05Sn0.01)[Be1.00O4]
chrysoberyl (main “z”) (Al1.95FeT0.05)[Be0.99Al0.01O4]
phlogopite (K0.75Na0.090.16)(Mg2.57FeT0.23Al0.20)[Si2.92Al1.08O10]([OH]1.57F0.43)
clinochlore (Mg4.23Al1.23FeT0.44MnT0.010.09)[Si2.89Al1.11O10]([OH]7.86F0.14)


sample: FKM-157
locality: Lovozero massif, Kola Peninsula, Murmanskaja Oblast’, Russia.
rock type: test.
major mineralogy: specimen acquired for mangan-neptunite.
(left: unpolarized light; right: under crossed polars)


sample: FKM-158
locality: Khit Ostrov, Karelia Republic, Russia.
rock type: corundum-garnet amphibolite. This sample shows some similarity to sample FKM-24, but that rock lacks garnet and its plagioclase is essentially end-member anorthite. This rock seems to have a lower bulk Mg/(Mg+Fe) ratio than FKM-24.
major mineralogy: Rock is predominately calcic amphibole and plagioclase (oligoclase). Porphyroblasts of large corundum (pink in hand sample) and smaller almandine garnet (only weakly zoned) are abundant. Scattered phlogopite is present, containing patchy chlorite. Along some of the amphibole-phlogopite contacts, the amphibole has been superficially altered to chlorite, and in one instance the secondary chlorite was further rimmed by a thin band of nearly end-member albite (this being in contact with a slightly higher-z zone of the adjacent mica). In both the corundum and the garnet, sparse small allanite-(Ce) grains, partially but significantly altered to REE-carbonates(?) are observed. Ilmenite (in part altering to rutile) and rutile by itself (perhaps after ilmenite?) make up the oxide phases. The rutile also contains ~1660 ppm Cr and ~963 ppm Zr as additional trace elements.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-158
corundum Al2.00O3
ilmenite (Fe2+0.94Mg0.05)Ti1.01O3
rutile (Ti0.99Fe3+0.01)O2
almandine (core) (Fe2+1.68Mg1.02Ca0.29Mn2+0.02)(Al1.93Fe3+0.06)[Si3.00O12]
almandine (rim) (Fe2+1.81Mg0.89Ca0.27Mn2+0.02)(Al1.94Fe3+0.06)[Si2.99Al0.01O12]
allanite-(Ce) (altered) (Ca0.97Na0.03)(Ca0.43Ce0.28La0.13Nd0.08Pr0.03Th0.02Sm0.01Sr0.01)Al0.97Al1.00
tschermakite (Na0.39K0.040.57)(Ca1.51Na0.39Fe2+0.09Mn2+0.01)(Mg2.31Al1.18Fe3+0.96Fe2+0.40Ti0.12V0.01Cr0.01Ni0.01)[Si5.77Al2.22O22]([OH]1.74O0.24F0.02)
phlogopite (main) (K0.78Na0.030.19)(Mg1.79FeT0.61Al0.45Ti0.10Cr0.01Ni0.010.03)[Si2.69Al1.31O10]([OH]1.79O0.19F0.02)
phlogopite (rim along secondary albite) (K0.68Na0.19Ba0.010.12)(Mg1.77FeT0.65Al0.44Ti0.09Cr0.01Ni0.010.03)
“partially chloritized mica” (K0.23Ca0.04Na0.01)(Mg3.00Al1.34FeT0.99Ti0.13V0.01Cr0.01Ni0.010.51)
clinochlore (rimming amphibole) (Ca0.03Na0.01)(Mg2.76FeT1.58Al1.22MnT0.01V0.01Cr0.01Ni0.010.40)[Si3.05Al0.95O10]([OH]7.99O0.0.01)
“oligoclase” (Na0.72Ca0.28)[Si2.68Al1.32O8]


sample: FKM-159
locality: Orford Nickel mine, St. Denis de Brompton, Estrie, Québec, Canada.
rock type: test.
major mineralogy: specimen acquired for diopside and grossular.
(left: unpolarized light; right: under crossed polars)


sample: FKM-160
locality: Mont Saint-Hilaire, Montérégie, Québec, Canada.
rock type: sodalite-nepheline syenite.
major mineralogy: test.
(left: unpolarized light; right: under crossed polars)


sample: FKM-161
locality: Picuris district, Taos Co., NM, USA.
rock type: test.
major mineralogy: specimen acquired for actinolite.
(left: unpolarized light; right: under crossed polars)


sample: FKM-162
locality: Kilbourne Hole, Doña Ana Co., NM, USA.
rock type: spinel peridotite xenolith in basalt.
major mineralogy: The basalt-hosted xenolith is predominately made up of coarse forsterite and chrome diopside, with subordinate enstatite and dark green spinel.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-162
spinel (Mg0.78Fe2+0.21Ni0.01)(Al1.80Cr0.18Fe3+0.01)O4
forsterite Mg0.99(Mg0.78Fe2+0.21Ni0.01)[Si1.01O4]
enstatite (Mg0.96Ca0.03Na0.01)(Mg0.69Fe2+0.19Al0.10Cr0.01)[Si1.89Al0.11O6]
diopside (core) (Ca0.74Na0.13Mg0.12)(Mg0.68Al0.19Fe2+0.06Fe3+0.03Cr0.02Ti0.01)[Si1.86Al0.14O6]
diopside (rim) (Ca0.85Mg0.11Na0.04)(Mg0.77Al0.10Fe2+0.07Cr0.02Ti0.02Fe3+0.01)[Si1.86Al0.13O6]


sample: FKM-163
locality: Graves Mtn., Lincoln Co., GA, USA.
rock type: argillaceous meta-quartzite. Metamorphosed quartz-sericite to argillic alteration assemblage.
major mineralogy: Lazulite, kyanite, muscovite, and an opaque (probably hematite), in a matrix of quartz of two distinct sizes. The larger quartz grains could possibly represent relict quartz eyes, suggesting that prior to metamorphism, and prior to the preceding advanced argillic alteration, the original rock may have been a quartz phenocryst porphyry.
(left: unpolarized light; right: under crossed polars)


sample: FKM-164
locality: Altay pegmatite, Fuyun Co., Xianjiang Autonomous Region, China.
rock type: metasomatized wallrock adjacent to Li pegmatite.
major mineralogy: specimen acquired for holmquistite.
(left: unpolarized light; right: under crossed polars)


sample: FKM-165
locality: Yates mine, Otter Lake, Outaouais, Québec, Canada.
rock type: allanite-titanite-scapolite-diopside carbonate rock. The descriptive but non-interpretational term “carbonate rock” is used here because there is debate as to whether rocks of this nature, in this region of the Grenville Province, are primarily metamorphic + metasomatic (and so would be classified as “marbles” or perhaps “skarns”), or whether they may have formed from melt fluxed by metasomatic fluids (and so might better considered as “crustal carbonatite”, or perhaps “carbonatitic migmatite”). The carbonate rocks occur in what are known as “vein-dikes”, again suggesting ambiguity between a metasomatic and a migmatitic origin.
major mineralogy: Salmon orange (in hand sample) calcite with abundant diopside, titanite, and scapolite intermediate between marialite and meionite. Scattered allanite is present, both as discrete crystals and as irregular rims between other minerals (e.g. between calcite and titanite, or between calcite and scapolite), and scattered apatite is also present. Minor quartz, zircon, and epidote (seemingly secondary) are present. The titanite contains ~916 ppm Zr.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-165
fluorapatite (Ca4.99Sr0.01Y0.01)[P2.97Si0.01S0.01O12](F0.69[OH]0.31)
titanite (Ca0.99Ce0.01)(Ti0.76Al0.19Fe3+0.03Nb0.01)(O0.77F0.19[OH]0.04)[Si0.99Al0.01O4]
allanite-(Ce) Ca0.99(Ca0.35Ce0.35La0.15Nd0.09Pr0.03Sm0.01[M+HREE]0.01Sr0.01)(Al0.87Fe3+0.12Ti0.02)Al1.00
epidote (alteration?) Ca1.00(Ca0.93Sr0.06)Al1.00Al1.00(Fe3+0.83Al0.16Mg0.01)(O0.99F0.01Cl0.01)[Si1.99Al0.01O7][Si1.00O4](OH)
diopside (Ca0.94Na0.05Mn2+0.01)(Mg0.66Fe2+0.26Fe3+0.04Al0.02)[Si1.98Al0.02O6]
phlogopite (K0.91Ba0.010.08)(Mg2.30FeT0.56Al0.05Ti0.02MnT0.010.06)[Si3.03Al0.97O10](F1.05[OH]0.89O0.04Cl0.02)
scapolite (“wernerite”) (Na1.48Ca1.32K0.17Sr0.03)[Si7.63Al4.36Fe3+0.01O24] . (Ca0.52Na0.42)([CO3]0.42Cl0.36[SO4]0.13)


sample: FKM-166
locality: Serra de Jacobina gold district, Bahia, Brazil.
rock type: tourmaline-fuchsite schist. Likely a metamorphosed sericite-dominant alteration assemblage, accompanying mesothermal “Mother Lode”-type Au mineralization.
major mineralogy: Predominately coarse bright green Cr-bearing muscovite (fuchsite), interlayered with abundant bands of Cr-rich oxy-dravite and quartz. Scattered chromite is also present. Reported M3+/∑M (M = Fe+Mn) and O/(O+OH) in the tourmaline analyses are estimations and have not been independently measured (although total Fe+Mn is low). For the low-Cr oxy-dravite only, values of M3+/∑M < 0.175 normalize to dravite instead of oxy-dravite.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-166
(poor stoichiometry;
re-analysis warranted)
oxy-dravite (most Cr-rich) (Na0.66Ca0.13K0.01Sr0.010.19)(Mg1.85Cr0.94Fe2+0.10Fe3+0.05Ti0.04V0.01)(Al5.88Fe3+0.12)
oxy-dravite (least Cr-rich) (Na0.56Ca0.23K0.010.20)(Mg2.14Cr0.57Fe2+0.12Fe3+0.12Ti0.03V0.01)(Al5.93Fe3+0.07)
muscovite (K0.82Na0.040.14)(Al1.68Cr0.15Mg0.13Ti0.08FeT0.04V0.010.91)[Si3.09Al0.91O10]([OH]1.79O0.16F0.05)


sample: FKM-167
locality: Graves Mtn., Lincoln Co., GA, USA.
rock type: kyanite-pyrophyllite schist. Metamorphosed advanced argillic alteration assemblage.
major mineralogy: Largely pyrophyllite with abundant scattered kyanite. Widespread, fine-grained, undifferentiated Fe-oxide; minor rutile and diaspore, and rare quartz; small amounts of a U(+) mineral of moderate relief and 1st order white birefringence… likely an alunite-group mineral, such as alunite, crandallite, or woodhouseite (update: confirmed by EPMA to be a zoned solid-solution of alunite-group minerals: typically a svanbergite core zoned outwards to a variably-zoned woodhouseite rim, and in places further overgrown with what appears to be a schlossmacherite; see composition table).
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-167
rutile (Ti0.98V~0.02)O2
diaspore? or böhmite? Al1.00O(OH)
“Fe-oxyhydroxide” (Fe3+0.97Al0.03)O(OH)
svanbergite-rich alunite
supergroup ss (core)
woodhouseite-rich alunite
supergroup ss (middle)
woodhouseite-rich alunite
supergroup ss (rim)
schlossmacherite-rich? alunite
supergroup ss (overgrowth)
kyanite (Al1.99Fe3+0.01)O[Si0.98Al0.02O4]
pyrophyllite Na0.01(Al1.99Fe3+0.020.99)[Si3.95Al0.05O10]([OH]1.97F0.03)


sample: FKM-168
locality: Picuris Range, Glenwoody district, Taos Co., NM, USA.
rock type: calc-silicate “skarn”.
major mineralogy: Zoisite (thulite?), vesuvianite, quartz, some garnet, and abundant As-rich apatite (up to 7.8 wt% [0.55 apfu] As).
(left: unpolarized light; right: under crossed polars)


sample: FKM-170
locality: Wagholi quarries, Wagholi, Pune district, Maharashtra, India.
rock type: cavities in zeolite facies metasomatized basalt.
major mineralogy: Cavansite and stilbite, with minor calcite.
(left: unpolarized light; right: under crossed polars)


sample: FKM-171 (billet courtesy of P. Lecumberri-Sanchez, Univ. Arizona)
locality: Prabornaz mine, Saint-Marcel, Val d’Acosta, Italy.
rock type: aluminoceladonite-biotite-braunite schist. 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: This sample was initially acquired for “alurgite”, a varietal name for red Mn3+-bearing muscovite. The non-opaque portion of the thin section contains two micas: an abundant slightly pleochroic buff- to pale tan-colored Mn-bearing dioctahedral mica (approximately aluminoceladonite; compositionally this mica seems to correspond best to “alurgite”), and a somewhat less abundant strongly pleochroic deep orange- to pale tan-colored Mn-bearing trioctahedral mica (approximately phlogopite; this mica probably contributes more of the deep red color to the more conspicuous phyllosilicate in hand sample). These micas are admixed with subordinate feldspars consisting of large and relatively abundant albite; untwinned K-feldspar (orthoclase?) of both relatively abundant Ba-poor (0.02 apfu Ba) and less abundant Ba-rich (up to ~0.11 apfu Ba) compositions; and minor stringers of hyalophane (0.40 apfu Ba), primarily along the margins between K-feldspar and mica. Small patches of variable-composition macfallite (an Mn-rich pumpellyite-like sorosilicate) are present. Scattered crystals of a zoned Mn-rich epidote group mineral ranging in composition from a patchy REE-enriched piemontite/tweddillite core to a high-REE tweddillite mid to outer rim with a subsequent piemontite overgrowth is also present (see the accompanying BSE image to see the zoning relationship in detail). The compositions corresponding to this zoning sequence (which is fairly consistent across multiple zoned grains) are presented in the table below. The analytical data for the most REE-enriched tweddillite composition in the table is also the focus of a YouTube video tutorial on “Normalizing epidote-group minerals in MS Excel“; see the “point #23” composition below. Although first described in 2001, the name “tweddillite” only survived until 2006 when the mineral was recommended to be renamed manganipiemontite-(Sr) (Armbruster et al., 2006), per new CNMMN nomenclature rules. In 2016, after years of prolonged community uproar over the simultaneous renaming of beloved “hancockite” to epidote-(Pb), the name tweddillite was reinstated (Revheim & King, 2016; [← subscription required]). Although not sufficiently enriched to appear in any of the listed formulas, all of the REE-bearing piemontite/tweddillite analyses also contain from ~1100 to ~2800 ppm Th; only the post-tweddillite REE-free piemontite overgrowth is Th-free. Two discrete sodic pyroxenes are present: scattered “spongy” slightly zoned aegirine primarily associated with the piemontite, and sparse blue(!) jadeite relict from the high pressure facies (one fairly small but recognizably blue crystal of this material is just barely visible in the unpolarized light image, near the top of the upper-left buff-colored muscovite mass). Scattered zircon and very minor barite are also present. In addition to the REE-bearing epidote-group minerals, REE minerals are represented by scattered cerianite and very sparse V-bearing “gasparite-(La)”. Interestingly, although gasparite-(Ce) was identified from other Alpine deposits in 1987, “gasparite-(La)” is not a presently recognized mineral. However, Cabella et al., 1999 [← subscription required] did report the occurrence of La-dominant REE[AsO4] from another Piedmont metamorphosed Mn deposit. The high-(La+Nd) but low-Ce content of this monazite-group mineral, comparable to the REE distribution observed in the REE-bearing piemontite/tweddillite analyses, is not indicative of an anomalously low-Ce system but rather of a high local oxidation state where Ce is preferentially stabilized as Ce4+ (viz. cerianite). In addition to the non-opaque minerals, the abundant opaque Mn-bearing phases consist primarily of a mixture of braunite, hollandite and cryptomelane (the latter two both Sr-enriched). Sample FKM-2 is also from the Prabornaz mine, but represents a different assemblage. Where the two assemblages share minerals in common, their compositions tend to differ. For example, relative to FKM-171, the piemontite (sensu lato) in FKM-2 contains notably more Fe and is essentially REE-free. The braunite in FKM-2 is also notably more Fe-enriched. Conversely, the K-feldspar in FKM-2 is less enriched in Ba than the feldspar in FKM-171. Sb was sought in all of the minerals of FKM-171 but was not found above its detection limit; in contrast, in FKM-2, some growth bands within the titanite were significantly Sb-enriched (up to ~0.12 apfu Sb; although, no titanite was observed in FKM-171).
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-171
cerianite (Ce4+0.91Mn4+0.03Th0.03Si0.02)O2
hollandite group ss
hollandite group ss
“gasparite-(La)” (La0.48Nd0.30Pr0.13Ce0.03Th0.03Ca0.01Sm0.01Sr0.01)[As0.51V0.34P0.14Si0.01O4]
braunite (Mn2+0.77Mg0.13Ca0.06Fe3+0.03)(Mn3+5.91Fe3+0.09)O8[Si0.97Al0.03O4]
macfallite (most Mg-rich) (Ca1.96Na0.01)Mn3+1.00(Al0.54Mn3+0.46)(Mn2+0.69Mg0.30)[Si2.02O7][Si1.02O4]([OH]2.85F0.09O0.07)
macfallite (most Al-rich) (Ca1.96Sr0.01K0.01)Mn3+1.00(Al0.61Mn3+0.36V0.02)(Mn2+0.82Mg0.15)[Si2.03O7][Si1.02S0.01O4]([OH]2.88O0.11F0.01)
epidote-group ss
(low z core)
epidote-group ss
(mod-low z core)
epidote-group ss
(mod z core inner rim)
epidote group ss
(high z mid-outer rim)
point #23
epidote-group ss
(v. low z overgrowth)
jadeite (Na0.91Ca0.07Mn2+0.02)(Al0.61Fe3+0.30Mg0.07Mn2+0.02)[Si2.00O6]
aegirine (Na0.90Ca0.09Mn2+0.01)(Fe3+0.77Al0.13Mg0.08Mn2+0.01Mn3+0.01)[Si1.99Al0.01O6]
aluminoceladonite (K0.910.09)(Al1.22Mg0.56MnT0.12FeT0.09Ti0.020.97)[Si3.60Al0.40O10]([OH]1.93O0.04F0.03)
phlogopite (K0.95Na0.010.04)(Mg1.92MnT0.39Al0.25FeT0.15Ti0.05Ni0.01Co0.010.20)[Si2.82Al1.18O10]([OH]1.84O0.11F0.05)
orthoclase? (main) (K0.92Na0.04Ba0.02Sr0.02)[Si2.93Al1.07O8]
orthoclase? (most Ba-rich) (K0.83Ba0.11Na0.05Sr0.01)[Si2.85Al1.14Mg0.01O8]
hyalophane (K0.59Ba0.40Na0.03)[Si2.58Al1.41MnT0.01O8]
albite (Na0.98K0.02)[Si2.97Al1.03O8]


sample: FKM-172 (billet courtesy of B. Jenkins, Freeport-McMoRan Copper & Gold Inc., Oro Valley office)
locality: El Hoyazo, Níjar, Almería, Andalusia, Spain.
rock type: lower crustal felsic granulite xenolith in calc-alkaline potassic magma.
major mineralogy: garnet, biotite, sillimanite (“fibrolite”).
(left: unpolarized light; right: under crossed polars)


sample: FKM-173
locality: N’Chwaning III mine, Kuruman, Kalahari manganese field, Northern Cape Province, South Africa.
rock type: quartz-pectolite-sugilite metasomatite. This rocks was originally a bedded Mn-rich sediment, that was subsequently metasomatized and metamorphosed.
major mineralogy: The sample is composed of an abundant, somewhat globular and vuggy MAl-dominant end-member of sugilite (this may be a new mineral), overgrown by similarly botryoidal sugilite sensu strictu (where Fe3+ dominates the M site). Within the sugilite are very tiny irregular grains of aegirine (relict?), whereas within the “Al-rich sugilite” are larger scattered patches of an amphibole gradational in composition between a relatively Li-enriched potassic richterite and a slightly Li-enriched sodic amphibole close to “potassic-magnesio-mangani-arfvedsonite” (which may also be a new species). Surrounding and interspersed with the sugilite masses are irregular discontinuous veinlets of quartz + pectolite (zoned in CL from pale centers to bright yellow rims). Also scattered throughout the rock but especially abundant along a coarse band rimmed by sugilite are small irregular clusters of several Ba-Sr-Mn silicates. These clusters are predominately Ba-bearing hennomartinite, with tiny overgrowths of Sr-bearing cherchiaraite-(Mn), and patches of a new ruizite-like mineral with both Ca sites occupied by Sr (cf. taniajacoite). Note that the reported Li contents for the sugilite, amphiboles and pectolite are estimates based on stoichiometry and charge balance constraints and have not been verified by instrumental means.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-173
hennomartinite (Sr0.90Ba0.11)(Mn3+1.99Fe3+0.01)[Si1.98O7](OH)2.00 . H2O
“SrSr-ruizite” Sr1.00(Sr0.82Ca0.18Na0.01)Mn3+1.99[Si3.99O11(OH)2]([OH]1.99F0.01) . 2H2O
cherchiaraite-(Mn) (Ba3.76Sr0.06Na0.03K0.01Ca0.010.13)(Mn3+3.69Fe3+0.010.30)
sugilite (rim) (K0.990.01)(Na1.990.01)(Fe3+1.11Mn3+0.72Al0.07Mn2+0.06Ti0.02Mg0.01)
“Al-sugilite” (core) (K0.990.01)(Na1.930.07)(Al1.10Mn3+0.57Fe3+0.27Mn2+0.04Mg0.02Ti0.01)
aegirine (Na0.96Ca0.03Mg0.01)(Fe3+0.88Mn3+0.05Mg0.04Al0.02Ti0.01)[Si2.00O6]
pectolite (Na0.93Li0.06Sr0.01)(Ca1.91Mn2+0.07Na0.02)[Si3.00O8(OH)]
potassic-richterite-rich amphibole ss (K0.65Na0.23Sr0.11)(Na1.36Ca0.59Li0.05)(Mg4.35Li0.26Mn3+0.25Fe3+0.13)
arfvedsonite”-rich amphibole ss


sample: FKM-174
locality: Načetín, Poběžovice, Plzeň region, Bohemia, Czech Republic.
rock type: Unclear, but this sample could possibly be a “ferro-dunite” that has undergone some metasomatism. Examples of “ferro-dunite” (but with olivine significantly more magnesian, and with magnetite as the dominant oxide) occur as mantle xenoliths in northern Bohemia (e.g. Ulrych et al., 2000).
major mineralogy: The rock is composed almost entirely of sub-parallel crystals of slightly enlongated olivine (Fa65Fo35). Patches and zones of amphibole (secondary?) are scattered around the olivine, and in some cases form clear alteration rims. This amphibole is essentially a ferri-tschermakite, although in places it approaches magnesio-hastingsite in composition. This amphibole itself shows zones of further alteration to tremolite, clinochlore and veinlets of an Al-bearing greenalite. Ilmenite forms large scattered masses, as well as veinlets penetrating the amphibole and olivine. Fine to less commonly more coarse exsolution of magnetite are associated with the ilmenite. Along one edge of the sample is a thick vein of greenalite that differs somewhat from the greenalite veinlets in the amphibole. The entire sample is highly fractured, primarily in two nearly-perpendicular directions that both parallel and cross-cut olivine crystals.
(left: unpolarized light; right: under crossed polars)

mineral representative mineral compositions in FKM-174
ilmenite (Fe2+0.95Mg0.03Mn2+0.02Fe3+0.01)Ti1.00O3
magnetite (Fe2+0.98Mg0.01Mn2+0.01)(Fe3+1.61Fe2+0.12Ti0.12V0.08Al0.05Cr0.01)O4
fayalite (Mg0.69Fe2+0.28Mn2+0.02)(Fe2+0.99Fe3+0.01)[Si0.99Fe3+0.01O4]
ferri-tschermakite-rich amphibole ss
ferri-tschermakite-rich amphibole ss
(approaching magnesio-hastingsite)
tremolite (Na0.14Ca0.07K0.010.78)(Ca1.65Fe2+0.33Mn2+0.02)(Mg3.70Fe2+1.26V0.02Sc0.01Ti0.01)
clinochlore (Mg3.48FeT1.25Al1.05MnT0.010.21)[Si2.95Al1.05O10]([OH]7.99O0.01)
greenalite (veinlets in amphibole) Ca0.01(FeT3.04Mg2.34Al0.26MnT0.050.31)[Si3.95Al0.05O10]([OH]7.97Cl0.02O0.01)
greenalite (veins in olivine) Ca0.01(FeT2.67Mg2.36MnT0.05Al0.010.91)[Si4.00O10](OH)8.00


sample: FKM-175
locality: Norra Kärr, Gränna, Jönköping, Småland, Sweden.
rock type: add rock type.
major mineralogy: specimen acquired for eckermannite (however, the occurrence of eckermannite at Norra Kärr is disputed, and the amphibole previously identified as eckermannite is now believed to be fluoro-leakeite).
(left: unpolarized light; right: under crossed polars)


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