STILPNOMELANE

Stilpnomelane is a potassium ferrous-iron aluminum silicate hydroxide hydrate mineral.
Ferristilpnomelane, is rare locally. The only known specimen of this mineral from Franklin was found in the Harvard University collection, together with an analysis by Jun Ito. This Franklin ferristilpnomelane is dark red, platy, massive, with vitreous luster, and is associated with hedenbergite, pyroxene, and calcite in one 4 cm specimen. Nothing is known of its geologic occurrence.
Ferrostilpnomelane, is uncommon locally. Only one occurrence is known. It occurs as massive, blackish, impure, foliated masses surrounding dendrites of rammelsbergite and gersdorffite at Franklin (Oen et al. 1984). It is also associated with barite, calcite, and sphalerite; small amounts of nickeline or fluorite may be present, but are not commonly seen in hand-specimen. Calculation of cations on the basis of the sum of octahedral and tetrahedral cations = 120, yield Fe = 22.8 and Mg = 20.4 atoms, indicating that this material is near a mid-member in the ferrostilpnomelane-lennilenapeite series. (Dunn, 1995)

Location Found:

Franklin

Mineral Note:

Ferrostilpnomelane is a variety of stilpnomelane noted for its being rich in ferrous iron. Ferristilpnomelane is another variety stilpnomelane. Both were used in earlier Franklin Mineral lists.

Year Discovered:

1827

Formula:

(K,Ca,Na)(Fe²⁺,Mg,Al,Fe³⁺)₈(Si,Al)₁₂(O,OH)₃₆ · nH₂O

Essential Elements:

Hydrogen, Iron, Oxygen, Potassium, Silicon

All Elements in Formula:

Aluminum, Calcium, Hydrogen, Iron, Magnesium, Oxygen, Potassium, Silicon, Sodium

IMA Status:

Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"

To find out more about this mineral at minDat's website, follow this link Stilpnomelane

References:

Dunn, Pete J. (1995). Franklin and Sterling Hill New Jersey: the world's most magnificent mineral deposits. Franklin, NJ.: The Franklin-Ogdensburg Mineralogical Society. p.472. 'Ferristilpnomelane, Ferrostilpnomelane'

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.78

The Picking Table References

	PT Issue and Page	Description / Comment
View Issue	V. 10, No. 1 - February 1969, pg. 6	Mineral Notes - Bannisterite/Ganophyllite/Stilpnomelane
View Issue	V. 6, No. 2 - August 1965, pg. 12	Stilpnomelane

Images


Stilpnomelane (green to metallic green and coppery red), dolomite (white-gray), calcite (white), and minor sphalerite, from Taylor Road Dump, Franklin, NJ. Photo by WP.


Stilpnomelane (coppery red and metallic green), dolomite (white-gray) and calcite (white), from Taylor Road Dump, Franklin, NJ. Photo by WP.