left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-451
locality: Mpita prospect, Kimbedi, Mindouli, Republic of Congo.
rock type: Cu-Zn silicate-dominated supergene alteration assemblage associated with a primary carbonate-hosted Cu-Pb-Zn MVT (Mississippi Valley type) ore deposit (De Putter & Nikis, 2016).
major mineralogy: The specimen was acquired for dioptase. Cerussite was originally also thought to be present, due to both a reported association with dioptase (see mindat) in the Mindouli district, and a strong off-white fluorescence of parts of the specimen matrix under SW-UV. Examination of the thin section suggested the fluorescent mineral to be willemite instead, also a reported association with dioptase in the Mindouli district, and subsequently verified by EDS; willemite and a Pb-bearing zoned dolomite dominate the rock. Scattered small patchy color-zoned (new color to bright lime green) mimetite is also present, as is some quartz. A curious coincidental feature of this sample is that all of the five dominant minerals present (dioptase, dolomite, willemite, quartz and mimetite) are hexagonal (or trigonal), and thus uniaxial.

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

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-452
locality: Přibyslavice, Kutná Hora, Bohemia, Czech Republic.
rock type: B- and P-bearing granite.
major mineralogy: The specimen was acquired for sarcopside and graftonite.

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-453
locality: Khibiny massif, Kola Peninsula, Murmanskaja Oblast’, Russia.
rock type: test.
major mineralogy: specimen acquired for nenadkevichite.

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-454 (Two thin sections cut from the same billet are shown here; the upper and lower image pairs represent samples FKM-454-1 [edge defects on the glass slide required a duplicate be made] and FKM-454-2, respectively).
locality: Toyofuku, Uki City, Kyushu Is., Japan.
rock type: plumasite “dike” in metasomatized (biotite-cordierite) peridotite.
major mineralogy: specimen acquired for corundum, hercynite, and oligoclase.

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-455
locality: Gilba valley, Brossasco, Piedmont, Italy (part of the Dora Maira massif).
rock type: whiteschist.
major mineralogy: specimen acquired for magnesiostaurolite.

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-456
locality: Bordvedåga (Høgtuva beryllium deposit), Høgtuva, Rana, Nordland, Norway.
rock type: add rock type.
major mineralogy: specimen acquired for phenakite, biotite and microcline.

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-457
locality: Bastnäs, Riddarhyttan, Skinnskatteberg, Västmanland, Sweden.
rock type: best described as a REE metasomatite.
major mineralogy: The specimen was acquired for ferriperboeite-(Ce), ferri-allanite-(Ce), cerite-(Ce), actinolite and quartz.

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-458
locality: Stary Gierałtów, Gmina Stronie Śląskie, Kłodzko County, Lower Silesian Voivodeship, Poland.
rock type: test.
major mineralogy: The specimen was acquired for kumdykolite in almandine

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-459 (billet from Univ. Arizona petrology collection; sample 12-8-65-1)
locality: Bearpaw Mountains, Hill Co., MT, USA. Based on rock descriptions in Bayley (1897), the sample could possibly be more specifically from Bearpaw Peak (now Baldy Mountain?), the highest point in the range.
rock type: although the sample has been labeled as “leucitite”, the rock appears to be mineralogically and geochemically consistent with lamproite (see next section); compare to sample FKM-460 (also labeled as leucitite), also from the same locality. The most appropriate name for the sample may be biotite-diopside-leucite lamproite.
major mineralogy: The specimen was acquired for leucite, although the large rounded “leucite” crystals are a pseudoleucite composite with only some leucite (relict? or late?) present. Although there may be some mineralogical variability, largely the composite crystals are composed of an inner “core” of a K-rich zeolite compositionally akin to a “K-mesolite” surrounded by an inner doughnut of K-feldspar and an outer doughnut of a somewhat Fe-enriched leucite. Abundant but still subordinate to the pseudoleucite balls are pale green diopside phenocrysts, grossly aligned and typically rimmed by a variable generally thin zone of bright-green aegirine-augite. Scattered orange weakly-zoned Ba- and Ti-enriched biotite is easily visible in PPL. Additional minor silicates include weakly-zoned forsterite and katophorite rootname amphibole enriched in K, F and Ti. The amphibole composition was best normalized to ∑(all cations) = 16, and the results plot near multiple nomenclature boundaries in Hawthorne et al., 2012, notably: A-site Na and K (three analyses all result in a “potassic-” prefix); and W-site F and OH (two out of three analyses yield a “fluoro-” prefix; however, this is further complicated by the calculated Ti-related WO, which will change if a different assumption is made and the small amount of T-site Fe3+ is exchanged with M-site Ti). Scattered Ti-rich magnetite and a strongly-zoned Ca-Sr-phosphate apatite are also present.

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-460 (billet from Univ. Arizona petrology collection; sample 12-8-65-3)
locality: Bearpaw Mountains, Hill Co., MT, USA. Based on rock descriptions in Bayley (1897), the sample could be more specifically from Bearpaw Peak, the highest point in the range.
rock type: leucitite; compare to sample FKM-459 (leucitite), also from the [the same locality].
major mineralogy: The specimen was acquired for leucite.

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-461 (billet from Univ. Arizona petrology collection; sample 100:1)
locality: Limburg-Weilburg, Giessen Region, Hesse, Germany.
rock type: limburgite porphyry.
major mineralogy: The specimen was acquired for augite, olivine and zeolites (philipsite?) filling amygdules.

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-462
locality: The simple mineralogy of this specimen is very similar to that of sample FKM-68, which is reportedly from the Longido area, Mt. Kilimanjaro region, Tanzania. Note: both of these presumed “Longido” specimens were purchased from lapidary suppliers and not a mineral dealer perhaps more accustomed to collectors’ desire of precise locality data. While FKM-68 was specifically labeled as from Longido, this cabochon was only labeled as being from “Tanzania”. As with sample FKM-68, it is in fact possible this sample actually does come from the more well-known nearby Mundarara mine locality.
rock type: corundum-zoisite-pargasite gneiss. Presumably a higher pressure (eclogite facies) equivalent of corundum-bearing amphibolite (i.e., akin to sample FKM-24); estimated at between 700°-850° C and between ~10-20 kbars, according to experimental phase relations. Note that unlike FKM-24, the amphibole in this sample is actually pargasite rather than tschermakite. Both this sample and FKM-24 (as well as FKM-68 and FKM-290) are thus granulite to eclogite facies metamorphic equivalents of what were probably originally gabbro to gabbroic anorthosite.
major mineralogy: The specimen was acquired for corundum, zoisite and pargasite.

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-463
locality: reportedly comes from “northwest Pakistan”; given its commercial name of “Khyber stone”, the locality can perhaps be slightly narrowed down to Pakistan’s Khyber Pakhtunkhwa province?
rock type: this is apparently a relatively new lapidary material from “northwest Pakistan”. Fashioned as cabochons, carvings and obelisks (but not yet observed as rough), it’s been variously sold as “snowflake obsidian” (not even close!), as “rhodonite” (due to the large very pale pink crystals in the dark matrix… also not correct), and a “porphyrite”, although the rock, while possibly originally igneous, now appears to be metamorphic.
major mineralogy: The specimen was acquired for “hornblende”.

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

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-464 (billet from Univ. Arizona petrology collection; the original sample was collected by Mark Barton during a field trip to the area, in conjunction with the 1994 GSA Annual Meeting in Seattle)
locality: Mount Baker area, WA, USA. Unfortunately, there are several outcrops of differing quartz diorite in the area, and it’s not known from which more specific locality this sample was collected.
rock type: two pyroxene quartz diorite.
major mineralogy: The specimen was acquired for plagioclase, clinopyroxene, orthopyroxene, hornblende, biotite and quartz.

accompanying videos: Short videos featuring the mineral associations and optical properties of the orthopyroxene, magnesio-ferri-hornblende and plagioclase in this thin section offer a more detailed look at this sample.

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-465 (billet from Univ. Arizona petrology collection; sample 8-27-60-18)
locality: Comobabi Mountains, Pima Co., AZ, USA.
rock type: hydrothermally-altered low-grade (prehnite-pumpellyite facies?) basalt.
major mineralogy: The specimen was acquired for epidote and pumpellyite.

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

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-466 (billet courtesy of Robert Madden [Microanalysis Australia, Perth]; sampled with permission from an early 1970s specimen curated by the Zimbabwe Geological Survey).
locality: ~60 km WNW of Karoi, in the Magondi metamorphic belt, Karoi district, Zimbabwe.
rock type: corundum-sillimanite-hercynite-borosilicate granulite unit, hosted in pyroxene-granulite-facies meta-sediment (latter as reported in Anderson, S. [1975] Grandidierite and kornerupine: two boron-bearing minerals new to Rhodesia. In: I.M. Kirkpatrick, ed., Annals of the Rhodesia Geological Survey, vol. 1; pp. 49-59.).
major mineralogy: Specimen acquired for grandidierite and additional borosilicates. Likely in significant part due to the abundance of opaque to near opaque oxides, the billet is very dark, and although several distinct phases where observed on the pre-polished billet surface, no specific minerals could be identified from the hand sample. Thin section mineralogy consists of abundant coarse grandidierite, with subordinate alkali-deficient tourmaline and hercynite (in places these are intergrown as a symplectite), biotite, sillimanite, and scattered corundum and ilmenite. Several scattered regions of prismatine are also present. Although not reflected in the empirical formula, ~1300 ppm Zn is present in the hercynite. For the purpose of the formula normalizations, the B contents of the grandidierite and tourmaline were assumed to be stoichiometric (B = 1.00 apfu and 3.00 apfu, respectively); the estimated B content of the prismatine, pending future in-house B analysis, presently was matched to the value reported by Grew et al., 1997 from the same locality (and likely the same assemblage, although werdingite was sought but not observed in this thin section). The rock is quartz-free and feldspar-free… although K is present in the mica, Na and Ca are both nearly absent.

accompanying videos: Short videos featuring the mineral associations and optical properties of the corundum, grandidierite, prismatine, tourmaline and biotite in this thin section offer a more detailed look at this sample.

left image: plane-polarized light (E-W); right image: under crossed polarizers; use slider in center to view more of either image

sample: FKM-467
locality: originally labeled only as “Badakhshan, Afghanistan”, but believed to be more specifically from one of several unnamed meta-evaporite occurrences outcropping below Ladjuar Madan (“Blue Mine”) at Sar-e-Sang.
rock type: high-grade meta-evaporite composed primarily of gypsum.
major mineralogy: The specimen was acquired for pargasite from an online vendor and was additionally described as “hosted in marble”; upon receipt of the hand sample, it was quickly confirmed that the “amphibole” was instead a pyroxene (with perfect “stop-sign”-shaped cross sections), and the host rock was non-reactive to dilute hydrochloric acid. Subsequent research on mindat found photos of several almost identical specimens; these and their descriptions allowed a more accurate assessment of the specimen mineralogy and also being able to pin down a more specific locality. Ultimately, the specimen actually consists of large euhedral crystals of light green diopside and scattered crystals and masses of pyrite in a matrix of primarily gypsum with subordinate anhydrite. From the hand sample, there is also possibly some scattered small pale violet marialite in the matrix (this will be checked in the thin section).

sample: FKM-468
locality: Hale Creek mine, Mad River Rock, Trinity Co., CA, USA.
rock type: test.
major mineralogy: The specimen was acquired for inesite.

sample: FKM-469
locality: Garpenberg, Dalarna Co., Sweden.
rock type: test.
major mineralogy: The specimen was acquired for inesite, diopside and galena.

sample: FKM-470
locality: Sanguozhuang, Dongchuan district, Kunming, Yunnan, China.
rock type: test.
major mineralogy: The specimen was acquired for veszelyite and hemimorphite.

sample: FKM-471
locality: Benallt mine, Gwynedd, Wales, UK.
rock type: test.
major mineralogy: The specimen was acquired for celsian.

sample: FKM-472
locality: Grupo di Voltri, Genova, Italy.
rock type: test.
major mineralogy: The specimen was acquired for barroisite.

sample: FKM-473
locality: Reported as from Kitka Valley, Kuusamo, Nordösterbotten, Finland, although according to mindat, “nuummite” (trade name for a metamorphic rock rich in “labradorescent” [schiller] ortho-amphibole; originally from Greenland) from Finland is so far only reported from Kainuanmäki, approximately 300 km to the NNE.
rock type: test.
major mineralogy: The specimen was acquired for “nuummite”, in this case thought to be barroisite rather than an ortho-amphibole.

sample: FKM-474
locality: Harstigen Mine, Pajsberg, Bergslagen mining district, Sweden.
rock type: test.
major mineralogy: The specimen was acquired for ferro-ferri-winchite and rhodonite.

sample: FKM-475
locality: Ohmi River, Itoigawa, Honshu Island, Japan.
rock type: test.
major mineralogy: The specimen was acquired for niigataite, clinozoisite, prehnite and diaspore.

next page (samples FKM-476 to FKM-500)

previous page (samples FKM-426 to FKM-450)