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sample: FKM-301
locality: Esquire No. 7 claim, Big Creek, Rush Creek deposit, Big Creek-Rush Creek district, Fresno Co., CA, USA.
rock type: test.
major mineralogy: The specimen was acquired for muirite and sanbornite.

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sample: FKM-302
locality: Kilbride, Isle of Skye, Scotland, UK.
rock type: test.
major mineralogy: The specimen was acquired for harkerite and monticellite.

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sample: FKM-303
locality: Franklin, Franklin mining district, Sussex Co., NJ, USA.
rock type: hardystonite-andradite-bustamite “metasomatite”. Granulite facies Zn-Mn-metasomatite..
major mineralogy: Large euhedral bustamite (essentially none to weak turquoise-colored SWUV fluorescence) and subhedral andradite garnet dominate the sample. Interstitial abundant hardystonite (strong blue SWUV fluorescence and cathodoluminescence) and lesser abundance “jeffersonite” clinopyroxene (near-boundary diopside-johannsenite compositions with an additional significant petedunnite component) are also present. Under BSE imaging, the hardystonite shows a main lower-z zone (enriched in Al and Na), and widespread higher-z patches enriched in Pb and Sr. Sparse inclusions of what appears to be hydro-andradite occur with the main andradite. Minor willemite is widely scattered in the sample, as inclusions in garnet and as streaks along fractures in the bustamite; the willemite is strongly cathodoluminescent and SWUV fluorescent in yellow-green (except apparently for one grain included in the “video” andradite, which while strongly cathodoluminescent appeared to lack any significant fluorescence). Sparse clinohedrite (orangish cathodoluminescence) occurs as small lone inclusions in garnet and as rims on willemite in garnet. Additional minor minerals include a single larger franklinite, one cluster of johnbaumite (orange cathodoluminescence; occurring with willemite in garnet), sparse calcite (red-orange cathodoluminescence; also in garnet) and scattered tiny barite.

accompanying videos: Short videos featuring the mineral associations and optical properties of the andradite, hardystonite, “jeffersonite” and bustamite in this thin section offer a more detailed look at this sample.

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sample: FKM-304
locality: Sterling Hill, Ogdensburg, Franklin mining district, Sussex Co., NJ, USA.
rock type: test.
major mineralogy: The specimen was acquired for kraisslite and franklinite. Numerous samples from the Franklin and Sterling Hill areas are represented among this collection; however, the only other arsenate-bearing sample is FKM-317, a sample from the Franklin mine containing one or potentially more members of the chlorophoenicite group.

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sample: FKM-305
locality: Água de Pau Massif, São Miguel Island, Azores, Portugal.
rock type: test.
major mineralogy: The specimen was acquired for fluornatropyrochlore and ferro-katophorite.

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

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sample: FKM-306
locality: Semiostrov’e, Keivy Mountains, Murmansk Oblast, Russia.
rock type: oligoclase-staurolite-quartz schist of the “staurolite zone”. Relative to typical metapelite compositions reflecting a mudstone protolith dominated by mica+chlorite+clay+quartz, this rock appears to be somewhat depleted in K (micas are not abundant and K-spar is absent), and somewhat enriched in Na+Ca (the growth of plagioclase porphyroblasts). Garnet, chloritoid, and kyanite are absent from this sample, although garnet and kyanite are reported for the locality.
major mineralogy: The specimen was acquired for staurolite. In hand sample, the large dark brown staurolite porphyroblasts largely occur as sharp and showy “St. Andrews cross” twins; in contrast, the large plagioclase porphyroblasts are not obvious in the hand sample, since feldspar is near the bottom of the crystalloblastic series and so the strongly poikioblastic crystals blend into the quartz-dominated matrix. Also visible in the hand sample (and the thin section as well) are abundant small rutile crystals and rutile/ilmenite intergrowths. The rutile contains up to 3100 ppm Nb, as well as minor Ta (up to ~170 ppm Ta) and W (up to ~130 ppm W). Minor but notable vanadium enrichments are observed in several of the minerals in the thin section, including the muscovite (up to ~1100 ppm V), biotite (up to ~1800 ppm V), and clinochlore (up to ~470 ppm V). Similar staurolite-bearing rocks further south, in Karelia, contrast to this sample in being notably enriched in Cr (for example, see sample FKM-32a); however, Cr-enriched staurolite-bearing rocks are also reported from the Kola area (for example, see sample FKM-309). Several minor accessory minerals are also present in the sample, including fluorapatite, zircon, monazite-(Ce) and xenotime-(Y).

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sample: FKM-307
locality: Mautia Hill, Kongwa, Kongwa District, Dodoma Region, Tanzania.
rock type: Because the original sample was essential a large crystal of Mg-orthoamphibole (anthophyllite-gedrite join), the precise nature of the greater rock type from which this specimen was recovered is subject to significant conjecture. However, mineralogically, it would appear to be from a moderate-grade metamorphic rock of likely an overall fairly Mg-rich bulk composition; similar Mg-rich rocks (although generally also considerably more Al-rich; i.e. kyanite-bearing), and of comparable and higher metamorphic grades, are well-known from this classic whiteschist locality. Although anthophyllite is described from some of the kyanite+talc whiteschists (for example, see Jöns & Schenk, 2004; also Chapter 5 in Jöns’ 2006 dissertation), this occurrence of very coarse Mg-orthoamphibole with some minor yoderite and talc (and also absent of all kyanite and quartz, at least at the scale of this sample) seems to be a quite atypical paragenesis, compared to the literature descriptions of anthophyllite at Mautia Hill. Since the entire Mautia Hill complex is presumed to have experienced a similar P-T path, however, perhaps the peculiarities of this specimen do not need to indicate an unusual retrograde reaction within the talc-kyanite whiteschist per se, but may rather alternatively represent a different protolith composition, for example a Mg-metasomatic rock formed along the contact of the kyanite-talc whiteschist with an adjacent Mg-rich rock (e.g. dolomitic marble)? Although outcrops overall are fairly limited in the Mautia Hill area, there do appear to be a few areas where such a contact may be exposed (for an overview geologic map of the locality with superimposed outcrop exposures, see Cutten et al., 2006). In any case, the plausibility of any conjecture on this unique specimen’s origins notwithstanding, some further insight into its petrogenesis could indeed be forthcoming: the dealer from whom I acquired the sample collected it himself, and so if I have an opportunity to speak with him at the next Tucson Gem & Mineral Show, I’ll be sure to ask him about it and to update this section with any additional information he can offer.
major mineralogy: The specimen was acquired for “green yoderite”. However, the sample appears to be just a large crystal of Mg-orthoamphibole (optically continuous; see crossed polarizer thin section scan), with scattered large yoderite inclusions, minor talc, rare small zircon, and notably (in the PPL thin section scan) abundantly-included with small to moderate-sized hematite and rutile; no kyanite or quartz are present. The amphibole crystal is internally shattered and was quite friable, resulting in some challenge in preparing the thin section billet. Compositionally, the amphibole has (B+C)[Mg/(Mg+Fe2+)] = ~0.93, along with 0.95 apfu TAl and 0.85 apfu CAl; this composition falls almost exactly halfway along the anthophyllite-gedrite join. Indeed, unlike some other aluminous orthoamphiboles where TAl incorporation is accompanied by concomitant ANa incorporation, this material contains almost no Na. The yoderite within the amphibole is nearly colorless in thin section, and so is visually distinct (and less striking) from the better-known indigo/purple yoderite variety, also found at Mautia Hill and intimately associated with kyanite and talc (featured here in samples FKM-69 and FKM-69b); nonetheless, the composition of this “pale green” yoderite differs only slightly from that of the indigo/purple yoderite in the other samples (primarily in minor Mn and Cr differences).

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

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sample: FKM-308
locality: The locality was given as “East Transbaikalia, Russia”, but the sample is more likely from one of the better known occurrences for blue diopside in the Prebaikalia (Pribaikal’e) region to the northwest, such as the Yoko-Dovyrensky Massif ~100 km N. of Lake Baikal.
rock type: high-grade calc-silicate “skarn”.
major mineralogy: The specimen was acquired for blue diopside (labeled as “violan”), although violan (sensu stricto: purple Mn3+-enriched omphacitic diopside) has not been previously reported from Russia. Indeed, the diopside in this sample is essentially of pure end-member composition, with all of the observed substituting elements limited to only ppm concentrations (however, one or more of these may be responsible for the blue cathodoluminescence present in the material; see below for more details). The pale blue color of the diopside in the hand sample thus isn’t colored directly by chromophore elements, but is plausibly the result of inter-valence charge transfer between the low but measurable levels of Fe and Ti present. The other dominant mineral in this sample is foshagite, which forms finely bladed/fibrous masses hosting the diopside crystals, although in one area of the sample, the foshagite appears coarser. Interestingly, the optical properties of the foshagite in this sample differ notably from those reported in the literature, although foshagite is reported from the locality and the composition was verified by microprobe analysis. Eakle, 1925) reports refractive indices of nα = 1.594, nβ = 1.594, nγ = 1.598, suggesting that then-presumed orthorhombic foshagite (now known to be triclinic) should be sensibly uniaxial positive, with a birefringence of δ = 0.004. In this sample, the maximum birefringence of the coarser material is somewhat greater, at 1st order pale yellow (δ = 0.010). Also unlike the literature data, this material is distinctly biaxial negative, with a 2V° of roughly 40° ± 10°. The dispersion is strong, as reported in the literature, but it’s not clearly the reported r > v, as it appears there may possibly be an additional horizontal(?) or more complex dispersion component superimposed on the axial angle dispersion. Another feature of the foshagite in this sample, also apparently not previously reported, is evidence for two orientations of polysynthetic twinning visible in the maximum birefringence section. All of these optical and crystallographic features are observable in the videos below. Matrix calcite is not notably present, although some calcite occurs intimately intergrown with the diopside, presumably co-crystallized as a product of a diopside-in reaction. Minor scattered hydroxylapatite (most very small but notably including one larger crystal) and numerous tiny scattered perovskite grains are both hosted in the foshagite.

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

[table “VIDEOS-FKM-308” not found /]
(note: stay tuned… videos pending)

Although not visible optically or in BSE imaging, the seemingly homogeneous diopside crystals in the sample show an interesting fine-scale patchy cathodoluminescence (CL) response under the electron beam, with abundant large “islands” of bright blue CL material within a CL-unresponsive host (see image above). The major element compositions of both portions are essentially identical, indicating ostensibly end-member diopside. Cathodoluminescence in pyroxenes has been attributed to both structural defects and to particular trace element activators (for example, in jadeite: Dopfel, 2006). The following table shows the minor/trace element differences between the two diopside components. Only those minor elements measured by EPMA using the PETRO_Silicate analytical routine (see the summary of analytical routines used on the UofA Cameca SX100 electron microprobe) and that were also above detection limits in at least one of the two diopside components are included in the table. Setting aside the possibility of a structural defect cause of the CL, the differences in Al and Ti contents in particular may be of interest as compositional activators, as these elements have been attributed to produce blue CL in other minerals.

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sample: FKM-309
locality: Kola Peninsula, Murmansk Oblast, Russia. Unfortunately, a more specific locality for the sample was not given. Fuchsite and similar sulfide/sulfarsenide mineralogy is reported from the ultramafic-associated Perchenga Ni-Cu ore field northwest of Murmansk, but it is unknown if [kyanite+staurolite]-bearing metamorphic rocks occur in the area, or if any localities in the area produce “fuchsite” available for the collector/lapidary market. Another Kola “fuchsite” locality, at Pestsovye Keivy and better known among collectors for staurolite twins (see sample FKM-306), does not report on the accessory mineral content, nor is the sample analyzed here Cr-enriched.
rock type: the rock is a staurolite-albite-kyanite-“fuchsite” schist, but is a bit of a curiosity, as it combines an ostensibly meta-pelite-like major mineral assemblage with the trace chemistry and accessory sulfides of an ultramafic rock. The protolith of this rock is unclear, but the somewhat unusual bulk chemistry may point to some kind of metamorphosed originally-metasomatic rock rather than just metamorphism of a simple sedimentary mudstone.
major mineralogy: The specimen was acquired for fuchsite and staurolite. The dominant mineralogy is relatively consistent with a moderately high-grade Al-rich meta-pelite, with abundant quartz, muscovite, plagioclase, staurolite, and kyanite. However, apparently absent is any relict protolith K-feldspar, nor are any lower-grade ferro-magnesian minerals such as chlorite, biotite (except for one very small cluster) or garnet present. In fact, staurolite is essentially the only Fe mineral present (there are also no Fe-oxides or Fe-Ti-oxides… only rutile is present), and Mg in the bulk rock is notable absent. The plagioclase is also somewhat atypical, as it is surprisingly low in Ca for a rock of this grade. Also unlike typical meta-pelite compositions, the chemistry of the silicate and oxide minerals here are notably enriched in Cr (see mineral composition table below); the muscovite is “fuchsite”, and both the staurolite and kyanite are sufficiently Cr-enriched to alter their usual colors/pleochroism in thin section. In addition to the Cr enrichment of the silicates, the accessory sulfide mineralogy is a diverse assortment of minerals more commonly encountered in ultramafic rocks. The several larger pyrrhotite masses are the most noticeable, but small equant crystals of gersdorffite are abundantly distributed throughout the rock. Included within the pyrrhotite are scattered masses of chalcopyrite, and in one place in the pyrrhotite are small “flames” of pentlandite. Further included within the chalcopyrite itself are tiny crystals of argentopentlandite. Locally the pyrrhotite shows clusters or veinlets of corroded bravoite, and it appears the bravoite developed from alteration of the pyrrhotite.

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sample: FKM-310
locality: Champion Mine, White Mountain Peak, White Mts, Mono Co., CA, USA.
rock type: test.
major mineralogy: The specimen was acquired for svanbergite.

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sample: FKM-311
locality: Snillfjord, Krokstadøra, Trondheim, Sør-Trondelag, Norway.
rock type: test.
major mineralogy: The specimen was acquired for thulite.

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sample: FKM-312
locality: MQ Granite AS quarry, Gaskkabeaivári, Kautokeino, Finnmark, Norway.
rock type: the rock is a piece of the Masi Quartzite, a “fuchsite”-bearing feldspathic meta-quartzite locally quarried as dimension stone.
major mineralogy: The specimen was acquired for Cr-enriched muscovite (“fuchsite”). The rock is predominately quartz, with subordinate microcline, Cr-bearing muscovite and Cr-bearing biotite. Accessory minerals include minor zircon and monazite-(Ce), as well as scattered pyrite; however, no Fe±Ti oxide minerals are present. Notable in this sample is an enrichment in a suite of elements more typically associated with mafic rocks (Cr and Ni in the micas; Co in the pyrite).

accompanying videos: Short videos featuring the mineral associations and optical properties of the Cr-bearing muscovite (“fuchsite”) in this thin section offer a more detailed look at this sample.

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sample: FKM-313
locality: In den Dellen quarries, Niedermendig, Mendig, Mayen-Koblenz, Rhineland-Palatinate, Germany.
rock type: test.
major mineralogy: The specimen was acquired for haüyne.

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

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sample: FKM-314
locality: Ali Abad, Hunza Valley, Gilgit District, Gilgit-Baltistan, Pakistan.
rock type: test.
major mineralogy: The specimen was acquired for pargasite.

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sample: FKM-315 (billet courtesy of R. Mielke [Cobalt, Ontario]; sample 628)
locality: Kipawa alkaline complex, Les Lacs-du-Témiscamingue, Abitibi-Témiscamingue, Québec, Canada.
rock type: metamorphosed alkali syenite.
major mineralogy: The specimen was acquired for rinkite-(Y), omphacite, fluoro-richterite and albite. Several additional samples from the Kipawa complex are featured as part of this collection and represent a variety of diverse mineral assemblages from the greater metamorphosed body; these include samples FKM-27, FKM-64, FKM-65 and FKM-211.

accompanying videos: Short videos featuring the mineral associations and optical properties of the fluorite, hiortdahlite, omphacite/aegirine-augite and microcline in this thin section offer a more detailed look at this sample.

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sample: FKM-316 (billet from the Univ. Arizona mineralogy collection; sample was orphaned and subsequently dis-used)
locality: this unlabeled sample is almost certainly from the classic Saranovskii mine, Saranovskaya village, Permskaya Oblast’ (middle Ural Mtns. region), Russia locality, or from one of the lesser-known adjacent localities in the same ore field.
rock type: hydrothermally altered and metamorphosed chromitite.
major mineralogy: The specimen was acquired for uvarovite and a Cr-rich pumpellyite group mineral. The garnet is bright green in PPL and anomalously birefringent under XP (with sector zones showing up to 1st order gray to white birefringence [tinted green from the underlying mineral color]), predominately Cr-rich grossular in composition but grading to Al-rich uvarovite along the rims. The pumpellyite group mineral is patchy zoned and ranges from 8.8 wt% to 20.4 wt% Cr2O3 (with ~14.0 wt% Cr2O3 in the main mod-z portions). These Cr concentrations suggest both Cr-rich pumpellyite-(Mg) sensu stricto and the YCr-dominant pumpellyite group mineral shuiskite (UPDATE: renamed in 2020 to shuiskite-(Mg), per pumpellyite group nomenclature recommendations, due to the 2019 discovery of [XCr-dominant]+[YCr-dominant] shuiskite-(Cr), also from the Saranovskii mine) are present. Unfortunately, as with the Cr-bearing tourmalines, Cr in pumpellyite group minerals may be partitioned between two different sites: the X-site (typically dominated by Mg, Fe2+, Fe3+, Mn2+ or Al; the major cation in this site is denoted in the mineral name by a suffix), and the Y-site (where the dominant cation defines the root name of the subgroup: YAl defines the pumpellyite sensu stricto subgroup and YCr defines the formerly lone-member shuiskite subgroup [and where YFe3+, YMn3+ and YV3+ define other, less well-known subgroups]); hence, knowledge of the precise distribution of Cr (and indeed other elements as well) between the X-site and Y-site is necessary to correctly identify the proper subgroup. Again also as with the Cr-bearing tourmalines, the distribution of Cr between the X-site and the Y-sites in pumpellyite group minerals cannot be determined unequivocally just by chemical analysis alone, and the correct cation assignment nominally requires an X-ray structural refinement. However, several researchers have attempted to ascertain if an underlying pattern to the Cr site occupancy can be elucidated that would further our understanding of how Cr is accommodated in pumpellyite group minerals. Most recent of these is Lykova et al., 2018 [← subscription required], which benefits from additional compiled data from several earlier structural refinements complementing their own data. Their conclusion is that for relatively low Cr concentrations, Cr prefers X-site occupancy, but at fairly high Cr concentrations, Cr increasingly begins to favor the Y-site. Using data presented in Lykova et al., 2018, the distribution of Cr between the X-site and Y-site of the three analyses presented below were estimated. The results are consistent with results from Lykova et al., 2018 for analyses of similar total (X+Y)Cr apfu (and note that this comparison is only to other samples from the Saranovskaya ore field, thus minimizing the possibility that any unrecognized Cr-partitioning effects due to differences in the regional P-T-X conditions at other localities might skew the observed relationship), and also appear to show some compelling trends in other elements. The garnet and pumpellyite, along with associated zoned Cr-rich clinochlore, occur as thin veinlets traversing the variably altered cumulate magnesiochromite. The alteration, most pervasive closest to the silicate veinlets but also prevalent along magnesiochromite grain edges elsewhere in the sample, shows marked enrichment in Fe (and normalizes as chromite). Interstitial to the magnesiochromite/chromite grains is additional Cr-rich clinochlore and sparse F-rich hydroxylapatite. Two other samples from the Saranovskii mine are also represented among the FKM thin section collection, but differ slightly in silicate alteration mineralogy from sample FKM-316; sample FKM-149 shares the uvarovite and clinochlore but lacks pumpellyite, whereas sample FKM-215 contains amesite rather than clinochlore, but also neither garnet nor pumpellyite.

accompanying videos: Short videos featuring the mineral associations and optical properties of the Cr-rich pumpellyite-(Mg)/shuiskite-(Mg) in this thin section offer a more detailed look at this sample.

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sample: FKM-317 (billet courtesy of M. Baum [Rockaway, New Jersey]; referred to in the sample’s accompanying paperwork as both #461 and mineral “E” [see below])
locality: Franklin Mine, Franklin Mining District, Sussex Co., NJ, USA.
rock type: test.
major mineralogy: this sample is a portion of a larger “reserve” specimen believed to contain, in part, a hydrous zinc-rich arsenate referred to on mindat.org as mineral “E”, and in Dunn et al., 1982 as “a second phase related to chlorophoenicite” and also as the museum catalog number NMNH 14909 of the specimen they originally examined. This material is purported to be a Zn-dominant end-member in the chlorophoenicite family, i.e. (Zn,Mg,Mn2+)3Zn2[AsO4](OH,O)6. Numerous samples from the Franklin and Sterling Hill areas are represented among this collection; however, the only other arsenate-bearing sample is FKM-304, a kraisslite-bearing sample from Sterling Hill.

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sample: FKM-318
locality: The original label listed only “Ural Mountains, Russia”, but the specimen is consistent with the material from the “pit 298” diggings or one of the adjacent diggings near the boundary of the Ilmen Nature Preserve in Chelyabinsk Oblast, Russia.
rock type: desilicified syenite pegmatite.
major mineralogy: The specimen was acquired for corundum, biotite and K-feldspar. Blocky crystals of zircon, xenotime or monazite were observed associated with the biotite clots, and members of the columbite/samarskite groups are reported from the locality.
(left: unpolarized light; right: under crossed polars)

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sample: FKM-319 (dealer sample number 2795)
locality: Vasin-Myl’k Mt, Voron’i Tundry, Murmansk Oblast, Russia.
rock type: phosphate-rich zone in a LCT-type granite pegmatite.
major mineralogy: The specimen was acquired for fairfieldite.

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sample: FKM-320 (dealer sample number 7101)
locality: Koashva Mt, Khibiny Massif, Murmansk Oblast, Russia.
rock type: agpaitic nepheline syenite.
major mineralogy: The specimen was acquired for paraumbite and eudialyte.

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

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sample: FKM-321 (dealer sample number 7100)
locality: Hatrurim Formation, Negev, Israel.
rock type: sanidinite facies pyrometamorphic phosphatic marble.
major mineralogy: The specimen was acquired for kalsilite.

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sample: FKM-322 (dealer sample number 4447)
locality: Izumrudnye Kopi area, Malyshevo, Yekaterinburg, Sverdlovsk Oblast, Russia. Margarite, specifically beryllian margarite, is explicitly noted on mindat as present in the Malyshevskaya pit, but is likely also present in other emerald occurrences within the ~25 km by ~2 km belt.
rock type: test.
major mineralogy: The specimen was acquired for margarite (possibly beryllian margarite).

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

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sample: FKM-323 (dealer sample number 2694)
locality: Rasvumchorr Mt, Khibiny Massif, Murmansk Oblast, Russia.
rock type: agpaitic nepheline syenite.
major mineralogy: The specimen was acquired for delhayelite.

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sample: FKM-324 (dealer sample number 4294)
locality: Jakobsberg Mine, Jakobsberg ore field, Nordmark district, Filipstad, Värmland, Sweden.
rock type: Although not associated with a causative intrusion, and indeed presumably formed by a completely different process, this mineralization style has been commonly referred to as a “Mn skarn”. A better term for this and related occurrences may be “calcareous Mn-metasomatite”. The original Fe and Mn were likely derived from exhalative hydrothermal processes, perhaps akin to those of modern seafloor “black smokers”. While enrichments of some of the associated elements such as As, Sb, Ba and Pb may have been contemporaneous, others such as Be and B were likely introduced later. Subsequent high-grade metamorphism (perhaps accompanied by additional metasomatism) facilitated the redistribution of elements into the diverse and unusual mineral assemblages we observe today.
major mineralogy: The specimen was acquired for ganomalite, Mn-bearing phlogopite and calcite.

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

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sample: FKM-325 (dealer sample number 3497)
locality: Popigai impact crater, Krasnoyarsk Krai, Russia.
rock type: test.
major mineralogy: The specimen was acquired for “maskelynite”, an impact glass of approximately plagioclase composition, and also if I’m lucky, possibly impact diamonds.

accompanying videos: Short videos featuring the mineral associations and optical properties of the “maskelynite” (plagioclase composition impact glass) in this thin section offer a more detailed look at this sample.

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