Stilpnomelane gallery

STILPNOMELANE Gallery Return to Stilpnomelane page. Click on image for larger view

STILPNOMELANE Moose Pocket, Albany, NH 3.1 cm specimen. Stilpnomelane spheres to 1 mm. STILPNOMELANE Moose Pocket, Albany, NH Stilpnomelane spheres to 1 mm. STILPNOMELANE Moose Pocket, Albany, NH Stilpnomelane spheres to 1 mm.	Species: STILPNOMELANE Locality: Moose Pocket, Albany, NH Specimen Size: 3.1 cm specimen. Stilpnomelane spheres to 1 mm. Field Collected: Bob Janules Catalog No.: A Bob Janules specimen Notes: This mineral has been identified as macaulyaite since 1997 based upon several EDS analyses. (See discussion with next photo.) A polished grain EDS analysis , BC239, set 24, from this specimen showed a Fe, Al silicate with a bit of potassium. The Fe+Al to Si ratio is way to low for macaulayite. An inquiry posted to the mindat.org messageboard gave a response suggesting that stilpnomelane was a better fit. Stilpnomelane, K(Fe²⁺,Mg,Fe³⁺)₈(Si,Al)₁₂(O,OH)₃₆·2H₂O , does not require aluminum, but can contain a significant amount. A comparison with the BC239 analysis and a webmineral analysis of stilpnomelane is given below.
STILPNOMELANE Moose Pocket, Blackberry Crossing, Albany, NH 2 cm specimen with 1 mm spheres of stilpnomelane	Species: STILPNOMELANE Locality: Moose Pocket, Blackberry Crossing, Albany, NH Specimen Size: 2 cm specimen with 1 mm spheres of stilpnomelane Field Collected: Bob Janules Catalog No.: u1038 Notes: This specimen had been identified as macaulayite, (Fe,Al)₂₄Si₄O₄₃(OH)₂ , for a couple of decades and was in my NH species display as macaulayite. The first (1997) EDS analysis of this Moose Pocket material was performed by Dr. Eugene Foord of the USGS. It was this analysis that first suggested macaulayite. A second EDS analysis (2002) for Art Smith by Excalibur was from a similar specimen from the Moose Pocket. This analysis is quite similar to the Foord analysis. Elements carbon and lighter do not give a response on this instrument. Note potassium, K, an essential element for siderophylite and muscovite is low in both plots. A third EDS analysis of this material, performed on a polished grain of the (then) NH display specimen #u1038, was done in Dec., 2011. The elemental response shown in this new plot is similar to the previous two. (This instrument detector has neglegable response below sodium) I now conclude that the small amount of potassium seen in these analyses, but previously ignored as insignificant, is a critical determinant in definining these specimens as stilpnomelane.
STILPNOMELANE Lovejoy Pit, Conway, NH 8 mm field of view. Bronze colored, micaeous stilpnomelane. STILPNOMELANE Lovejoy Pit, Conway, NH 2 mm field of view. Bronze colored, micaeous stilpnomelane.	Species: STILPNOMELANE Locality: Lovejoy Pit, Conway, NH Specimen Size: Zoom views of specimen 1943. Top: 8 mm fov. Bottom: 2 mm fov Field Collected: Gift from Bob Janules Catalog No.: 1943 Notes: Bronze colored, stellate, micaeous stilpnomelane on albite.
STILPNOMELANE Lovejoy Pit, Conway, NH 8 cm specimen of quartz, microcline and bronze colored, micaeous stilpnomelane.	Species: STILPNOMELANE Locality: Lovejoy Pit, Conway, NH Specimen Size: 8 cm specimen of quartz, microcline and bronze colored, micaeous stilpnomelane. Field Collected: Carl Francis Catalog No.: Harvard # 123545 Notes:
STILPNOMELANE Moat Mtn., Hale's Location, NH 4 cm specimen with miarolitic cavity of albite, quartz, and muscovite with brown micaeous coating of stilpnomelane	Species: STILPNOMELANE Locality: Moat Mtn., Hale's Location, NH Specimen Size: 4 cm specimen with miarolitic cavity of albite, quartz, and muscovite with brown micaeous coating of stilpnomelane. Field Collected: Don Swenson - 1993 Catalog No.: 1959 Notes: Don saved this specimen for the 2.5 mm cluster of cassiterite crystals in the lower middle of the specimen. Small bertrandite crystals are also present. Don gave me this specimen in September, 2015.
STILPNOMELANE Government Pit, Albany, NH 6 mm field of view STILPNOMELANE Government Pit, Albany, NH 3 mm field of view STILPNOMELANE Government Pit, Albany, NH 2 mm field of view	Species: STILPNOMELANE Locality: Government Pit, Albany, NH Specimen Size: 6 mm field of view. Stilpnomelane on microcline. FOV's for zoom views as annotated. Field Collected: Found in large box of uncleaned, untrimmed, Government Pit specimens collected by Leroy Grant of Albany, NH (deceased). Collected in the 1970's. Catalog No.: u2229 Notes: In comparison with mindat.org stilpnomelane specimens, this one is very nice. From a stack of 95 images using a Bosh & Lomb microscope objective with my Canon G9 camera. Stilpnomelane chemistry is (mindat.org): (K,Ca,Na)(Fe,Mg,Al)₈(Si,Al)₁₂(O,OH)₃₆ · nH₂O A carbon tape mounted grain EDS analysis (BC303, set 21) calculated an APFU chemistry of: (K_0.43,Ca_0.56)_Σ=0.99(Fe_4.41,Al_3.79)_Σ=8.2Si₁₂O₁₀₉ , normalized for 12 Si. This computed formula assigns all the Al to the (Fe,Al) group to make the chemistry match best possible. With this convenience, the analysis matches the mindat formula quite well. No Na or Mg substitutions were detected in this Government Pit sample.
STILPNOMELANE Government Pit, Albany, NH 17 mm field of view. Bronze, micaeous, stilpnomelane clusters on microcline & quartz. STILPNOMELANE Government Pit, Albany, NH 0.9 mm close-up view	Species: STILPNOMELANE Locality: Government Pit, Albany, NH Specimen Size: 17 mm field of view. Bronze, micaeous, stilpnomelane clusters on microcline & quartz. 0.9 mm close-up. Field Collected: Leroy Grant - 1970's Catalog No.: 2132 Notes: The 17 mm FOV is a no stacking shot.