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

sample: FKM-126
locality: Lewis mine, Willsboro, Essex Co., NY, USA.
rock type: grossular-diopside-wollastonite calc-silicate. Pyroxene hornfels facies presumably argillaceous metacarbonate or calcareous argillite (“marl”).
major mineralogy: This attractive rock is from a well-known locality and specimens are featured in many university petrology collections. The sample is predominantly almost mono-mineralic coarse wollastonite (bright yellow CL), with local bands of additional small diopside and/or small garnet (indicative of compositional variations in the original protolith). The pyroxene is compositionally homogeneous, but the garnet is overall weakly zoned, generally grossular in the main bulk but with small patchy interior zones more Fe-rich and close to the grossular-andradite composition boundary; very thin rims on many of the garnet grains are sufficiently Fe-rich to be well into the andradite composition field. Bits of quartz (relict and/or metamorphic reaction product?) and scattered fluorapatite (blue CL) are also present in the sample, as well as thin veinlets of secondary calcite that traverse the rock.

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

sample: FKM-127
locality: Hiassu farm, Itaju do Colônia, Bahia, Brazil.
rock type: carbonatite-associated sodalite syenite.
major mineralogy: test.

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

sample: FKM-128 (billet courtesy of G. Färber, Gunnar Färber Minerals)
locality: Ruoutevare, 13 km N of Kvikkjokk, Lappland, Sweden.
rock type: test.
major mineralogy: Reported to contain magnesiohögbomite-2N2S, but no högbomite-family minerals are present in this thin section.

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

sample: FKM-129 (billet courtesy of J. Aleinikoff, U.S.G.S.-Denver; host rock of the R33 zircon geochronology standard [419±1 Ma])
locality: Braintree complex, near Randolph, VT, USA.
rock type: reported as a biotite-hornblende monzodiorite by Black et al., 2004, this particular sample contains no potassium feldspar but is extensively altered (deuteric?) and many of the minerals are notably Fe-enriched; hence, ferro-diorite or even quartz ferro-diorite (assuming the quartz present is igneous and not metasomatic) may be a more appropriate name in this case.
major mineralogy: This rock is notable for the scattered millimeter-sized zircons that are widely used as a geochronology standard (Black et al., 2004), which at first appearance due to their high relief and birefringence look much like olivine under the microscope. The EPMA analyses presented here include data not only from the FKM-129 thin section, but also from one or more earlier thin sections and epoxy mounts originally prepared to better characterize the zircon host rock. Although these various sample sources are not differentiated among the analyses here, keep in mind that some minor mineralogical and geochemical variability between them is possible. The original presumably calcic plagioclase in FKM-129 has been converted to near end-member albite crowded with tiny epidote porphyroblasts. Many of these epidote crystals show a distinct clinozoisite core with a variably Fe-enriched epidote overgrowth; some of this overgrowth epidote shows mild enrichments in Sc, Y and REE (although more so in some of the other Braintree Complex samples than in this particular thin section). Two relict(?) zoned allanite-(Ce)/REE-rich epidote grains were discovered through X-ray mapping. The dominant ferro-magnesian minerals are an Fe-rich biotite and an amphibole with patchy zoning compositionally between magnesio-ferri-hornblende and ferro-ferri-tschermakite (along with minor Fe-rich chlorite that occurs as an alteration of the biotite and amphibole). Abundant large enlongated and commonly curved or bent laths of ilmenite are present, and a single relatively large titanite was found through X-ray mapping. Scattered quartz (orange CL) is present and appears to be late igneous rather than metasomatic. Scattered fluorapatite and a single celestite (the latter likely derived from the breakdown of the plagioclase) are also present. One large somewhat irregular-shaped pyrite was observed, which displays a fairly sharp zonation; one portion was Co-enriched (~2.4 wt% Co) and the other was Co-free and also hosted a few small scattered pyrrhotite grains. The entire sulfide clot was rimmed by “limonite”.

The following zircon 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 MAD-green zircon standard (Mazdab & Wooden, 2006). The data were collected over two different sessions; the latter session included a then more extensive element list. 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, although the standards really are pretty remarkable for being natural materials.

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

sample: FKM-130 (billet courtesy of D. Bradley, U.S.G.S.-Anchorage)
locality: “eudialyte prospect”, Windy Fork granite pluton, McGrath distict, Alaska Range, AK, USA.
rock type: test.
major mineralogy: eudialyte.
accompanying videos: Short videos featuring the mineral associations and optical properties of the eudialyte in this thin section offer a more detailed look at this sample.

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

sample: FKM-131 (self-collected in July 1996)
locality: Mary Kathleen mine, near Mary Kathleen townsite (abandoned), northwest QLD, Australia.
rock type: “skarn”-like calc-silicate metasomatite.
major mineralogy: Predominately massive andradite garnet, with abundant allanite-(Ce), scattered diopside, fluorapatite and pyrite, and sparse stillwellite-(Ce).
accompanying videos: Short videos featuring the mineral associations and optical properties of the allanite in this thin section offer a more detailed look at this sample.

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

sample: FKM-132
locality: Armstrong Farm, near Johnsburg township, Warren Co., NY, USA.
rock type: test.
major mineralogy: serendibite, sinhalite.

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

sample: FKM-133
locality: Zillertal, Austria.
rock type: magnesite-talc-“serpentine” schist. The sample is greenschist facies, with a likely protolith of some type of carbonate-metasomatized ultramafic rock (although a bit high in Al).
major mineralogy: Inspection of the hand sample shows what appears to be porphyroblasts of a brownish rhombohedral carbonate in a chlorite schist matrix. The carbonate is ferroan magnesite (= “breunnerite”). Note the lack of polysynthetic twinning in the magnesite (in the crossed polar image), which differentiates it from calcite and also the dolomite-group carbonates (compare this sample to the very similar appearing FKM-115, which however contains dolomite rather than magnesite). In thin section, the dominant sheet silicate has gray birefringence, although at a very fine-scale, areas of higher birefringence are also visible. Coarser blades of talc (and with “invisible” talc likely contributing to the higher birefringence of some of the fine-grained material) are also visible. Under BSE imaging, the coarse talc can be subtly differentiated the from finer-grained dominant sheet silicate, which appears homogeneous. However, analyses of the dominant sheet silicate do not normalize well to either an 8[OH] sheet silicate (chlorite and serpentine-kaolinite groups) or to a 2[OH] sheet silicate (mica and talc-pyrophyllite groups), and in fact appear to be intermediate between the two (and chlorite, talc and mica analyses from other samples done with the same calibration normalized as expected). Based on the analyses of this sample, the sheet silicate could be effectively normalized to a mixed layer composition of approximately 2:1 ratio of talc to an aluminous serpentine (and is presented in the composition table as such). Interlayering in sheet silicates is probably more common than appreciated, and may be suspected macroscopically when carefully done analyses yield unusual stoichiometries (see for example Veblen, 1983 [and references therein]). It is certainly possible that true interlayering is not present, but rather that the mono-mineralic domains are simply at a finer scale than discernible with microprobe beam resolution; this question could be resolved with TEM imaging. Abundant small porphyroblasts of ilmenite are present, as well as scattered tiny zoned rutile, apatite and monazite. Trace elements in the zoned rutile include ~93 ppm Zr, ~186 ppm Sn and ~243 ppm Cr in the low-z portion, and ~276 ppm Zr, ~155 ppm Sn and ~356 ppm Cr in the high-z portion.

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

sample: FKM-134
locality: unlabeled, but believed to be from Armstrong Farm, near Johnsburg township, Warren Co., NY, USA.
rock type: test.
major mineralogy: serendibite.

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

sample: FKM-135
locality: unlabeled, but believed to be from one of the NY or Madagascar serendibite/grandidierite occurrences.
rock type: test.
major mineralogy: serendibite.
accompanying videos: Short videos featuring the mineral associations and optical properties of the serendibite in this thin section offer a more detailed look at this sample.

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

sample: FKM-136
locality: San Vito quarry, San Vito, Ercolano, Monte Somma, Somma-Vesuvius complex, Naples province, Campania, Italy.
rock type: metasomatized(?) sanidinite facies meta-calcareous ejectum.
major mineralogy: Scattered meionite crystals along the N and E edges of the the thin section (these were growing into open vugs), in a largely carbonate matrix.

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

sample: FKM-137 (billet from Univ. Arizona petrology collection)
locality: unlabeled, but believed to be from the Stillwater complex, MT, USA.
rock type: orthopyroxenite (“bronzitite”).
major mineralogy: Essentially only orthopyroxene.
accompanying videos: Short videos featuring the mineral associations and optical properties of the enstatite in this thin section offer a more detailed look at this sample.

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

sample: FKM-138
locality: Spurr mine, Imperial Heights, Baraga Co., MI, USA.
rock type: chloritoid phyllite. Lower greenschist facies metamorphism of a probably siliceous argillaceous ironstone.
major mineralogy: The original sample was a large disk-shaped mass with a shiny “phyllitic” sheen that appears to be an essentially mono-mineralic crystal of chloritoid. This may have weathered out or been broken out of its original rock matrix. In thin section, the crystal is largely optically-continuous (although where it isn’t, that may be the result of twinning or of the intergrowth of the monoclinic and triclinic polytypes). There is a rich porphyroblast assemblage. Near end-member muscovite is one of the dominant inclusions; in places it it intergrown with a notably more Fe-rich muscovite. Fe-rich chlorite (chamosite) is also abundant. It is not entirely clear if all of the sheet silicates represent prograde phases (either incompletely-reacted relict material or prograde reaction products) or if some of the mica and chlorite are alteration (retrograde) products after chloritoid. Intimately intergrown with some of the chlorite are large irregular masses of fluorapatite. Ilmenite is abundant and widely scattered (in places forming rich clusters; these seemingly formed in-place at the expense of some precursor Ti-bearing mineral). Small HREE-enriched xenotime (not quantitatively analyzed) is relatively abundant and appears to be the only high z phase present in the sample. Quartz is abundant and may be both relict and new growth.

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

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

sample: FKM-139 (billet from Univ. Arizona petrology collection. Two thin sections cut from the same billet are shown here; the upper and lower image pairs represent samples FKM-139-1 [broken during use as an in-class teaching sample] and FKM-139-2, respectively).
locality: unlabeled, but believed to be from El Paso Co., CO, USA.
rock type: alkali granite pegmatite.
major mineralogy: Quartz, microcline perthite, riebeckite, aegirine, biotite.
accompanying videos: Short videos featuring the mineral associations and optical properties of the riebeckite in this thin section offer a more detailed look at this sample.

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

sample: FKM-140
locality: Fuka mine, Fuka, Bicchi-cho, Takahashi City, Okayama prefecture, Japan.
rock type: tilleyite-bearing marble. Sanidinite facies metacarbonate.
major mineralogy: test.

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

sample: FKM-141
locality: Laytonville quarry, Laytonville, Mendocino, Co., CA, USA.
rock type: test.
major mineralogy: specimen acquired for howieite, riebeckite and stilpnomelane.
accompanying videos: Short videos featuring the mineral associations and optical properties of the stilpnomelane in this thin section offer a more detailed look at this sample.

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

sample: FKM-142
locality: Galgenberg, near Leoben, Steirmark, Austria.
rock type: test.
major mineralogy: specimen acquired for chloritoid.
accompanying videos: Short videos featuring the mineral associations and optical properties of the chloritoid in this thin section offer a more detailed look at this sample.

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

sample: FKM-143
locality: Iron Cap mine, Graham Co., AZ, USA.
rock type: test.
major mineralogy: specimen acquired for johannsenite.
accompanying videos: Short videos featuring the mineral associations and optical properties of the johannsenite in this thin section offer a more detailed look at this sample.

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

sample: FKM-144
locality: Hålsjöberg, Torsby, Värmland, Sweden.
rock type: test.
major mineralogy: specimen acquired for wyllieite and scorzalite.

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

sample: FKM-145
locality: Norra Kärr, Gränna, Jönköping, Småland, Sweden.
rock type: test.
major mineralogy: specimen acquired for eudialyte and catapleiite.
accompanying videos: Short videos featuring the mineral associations and optical properties of the mosandrite, eudialyte, aegirine and magnesio-fluoro-arfvedsonite in this thin section offer a more detailed look at this sample.

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

sample: FKM-146
locality: Norra Kärr, Gränna, Jönköping, Småland, Sweden.
rock type: test.
major mineralogy: specimen acquired for rosenbuschite.
accompanying videos: Short videos featuring the mineral associations and optical properties of the fluorite and nepheline in this thin section offer a more detailed look at this sample.

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

sample: FKM-147
locality: Laytonville quarry, Laytonville, Mendocino, Co., CA, USA.
rock type: deerite-stilpnomelane-zussmanite metaquartzite. Blueschist facies ferruginous metaquartzite.
major mineralogy: Quartz and zussmanite are the dominant minerals in this sample, with subordinate deerite and a K-deficient stilpnomelane. Minor apatite, chalcopyrite and pyrrhotite are also present, as well as a sparse poikioblastic allanite zoned from a La-rich ferriallanite core to a Nd-rich allanite. This material was challenging to analyze due to prolific fine quartz inclusions, and the measured Si concentrations from both the core and rim analyses were corrected for a small amount (less than 2%) of quartz contamination (to force normalized Si = 3.00). The relative enrichments in La and Nd relative to Ce in these allanites are likely a function of locally high redox conditions and a resulting higher-than-typical Ce4+/∑Ce ratio (and so less Ce3+ available for allanite). This sample is from the same locality as samples FKM-15 and FKM-141, also from blueschist facies ferruginous metaquartzite, but of somewhat differing protolith bulk compositions and hence differing alkali-Fe-silicate mineralogy. Normalization of stilpnomelane and zussmanite are complex owing to possible vacancies in the A and M sites, variable Fe3+ and/or Mn3+ in the M site, and potentially variable hydroxyl (in both minerals) and excess water (in stilpnomelane). For this sample, the stilpnomelane is normalized to three assumptions: (a) 20 T+M cations (permits no vacancies in the M site), (b) 6[OH] per 36 total [O+OH] (this conforms to a sheet silicate T4O10 skeleton and also yields a reasonable M3+/∑M [M = Fe+Mn] ≈ 0.37), and finally (c) 5 moles of excess H2O (which brings the overall total to almost exactly 100 wt%). The normalization is similar to that of the stilpnomelane in FKM-15. The zussmanite was similarly normalized to (a) 30 to 31 A+M cations (permits up to one vacancy in the M site, and allows flexibility in estimating a reasonable M3+/∑M [M = Fe+Mn]… in this case, ~0.17)) and (b) 14[OH] per 56 total [O+OH] to provide a constraint on the charge balance.
accompanying videos: Short videos featuring the mineral associations and optical properties of the zussmanite in this thin section offer a more detailed look at this sample.

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

sample: FKM-148
locality: near Gascoyne Junction (Brockman Creek?), WA, Australia.
rock type: reported to be a kimberlite, but this sample actually is an olivine nephelinite (i.e., compare this sample with another example of nephelinite FKM-113, and also with a classic kimberlite FKM-103). The sample appears to be somewhat agglomeratic.
major mineralogy: Phenocrysts of large strongly-zoned forsterite in a matrix of intergrown very fine nepheline and somewhat coarser, slightly-zoned clinopyroxene (sometimes as crystal sprays). From multiple analytical spots, the nepheline did not give a good analyses, due in part to the very fine grain size, possible admixture with other material, and likely alkali migration caused by the electron beam. A zoned Cr-rich (core) to Fe-Ti-rich (rim) spinel is also prevalent, as is scattered apatite and rare Ni-(Cu)-sulfide. Minor chlorite alteration is locally present.
accompanying videos: Short videos featuring the mineral associations and optical properties of the forsterite and diopside in this thin section offer a more detailed look at this sample.

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

sample: FKM-149
locality: Saranovskii mine, Saranovskaya village, Permskaya Oblast’ (middle Ural Mtns. region), Russia.
rock type: hydrothermally altered and metamorphosed chromitite.
major mineralogy: Sector zoned birefringent uvarovite with minor intergrown calcite, filling veins in a massive granular chromite-magnesiochromite ss. Minor alteration chromian clinochlore is also present. Two other samples from the Saranovskii mine are also represented in this collection, but differ slightly in mineralogy from sample FKM-149; sample FKM-316 shares the uvarovite but additionally contains shuiskite, whereas sample FKM-215 only contains chromian amesite.

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

There is currently no sample FKM-150.

next page (samples FKM-151 to FKM-175)

previous page (samples FKM-101 to FKM-125)