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Highslide JS
STILPNOMELANE   Moose Pocket, Albany, NH
3.1 cm specimen. Stilpnomelane spheres to 1 mm.


Highslide JS
STILPNOMELANE   Moose Pocket, Albany, NH
Stilpnomelane spheres to 1 mm.


Highslide JS
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 analysis compare

Highslide JS
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.
Highslide JS
STILPNOMELANE   Lovejoy Pit, Conway, NH
8 mm field of view. Bronze colored, micaeous stilpnomelane.


Highslide JS
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.
Highslide JS
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:
Highslide JS
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.
Highslide JS
STILPNOMELANE   Government Pit, Albany, NH
6 mm field of view


Highslide JS
STILPNOMELANE   Government Pit, Albany, NH
3 mm field of view


Highslide JS
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:
(K0.43,Ca0.56)Σ=0.99(Fe4.41,Al3.79)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.