Stilpnomelane

{{infobox mineral

| name = Stilpnomelane

| boxwidth =

| image = Stilpnomelane-217448.jpg

| alt =

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| category = Phyllosilicates
Smectite group

| formula = {{chem2|K(Fe(2+),Mg,Fe(3+))8(Si,Al)12(O,OH)27*n(H2O)}}

| IMAsymbol = Stp{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}

| molweight =

| strunz = 9.EG.40

| dana =

| system = Triclinic

| class = Pinacoidal ({{overline|1}})
(same H-M symbol)

| symmetry = P{{overline|1}}

| unit cell = a = 21.72 Å, b = 21.72 Å
c = 17.4 Å; α = 124.14°
β = 95.86°, γ = 120°; Z = 6

| color = Black, greenish black, yellowish bronze, greenish bronze

| colour =

| habit = Platey, scaly and fibrous with comb structures; radiating groups

| twinning =

| cleavage = Perfect on {001}, imperfect on {010}

| fracture =

| tenacity = Brittle

| mohs = 3–4

| luster = Vitreous to dull

| streak = Gray white

| diaphaneity = Subtranslucent to opaque

| gravity = 2.77 – 2.96

| density =

| polish =

| opticalprop = Biaxial (−)

| refractive = n_α = 1.543 – 1.634 n_β = 1.576 – 1.745 n_γ = 1.576 – 1.745

| birefringence = δ = 0.033 – 0.111

| pleochroism = X: bright golden yellow to pale yellow

Y and Z: deep reddish brown, to deep green to nearly black

| 2V = 0–40 measured

| dispersion = None

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| references = [http://www.handbookofmineralogy.org/pdfs/Stilpnomelane.PDF Handbook of Mineralogy][http://www.mindat.org/min-3789.html Stilpnomelane on Mindat][http://www.webmineral.com/data/Stilpnomelane.shtml Stilpnomelane on Webmineral]

}}

Stilpnomelane is a phyllosilicate mineral. It has the chemical formula {{chem2|K(Fe(2+),Mg,Fe(3+))8(Si,Al)12(O,OH)27*n(H2O)}}.

Stilpnomelane occurs associated with banded iron formations. It is a metamorphic mineral associated with the blueschist and greenschist facies.

It was first described in 1827 for an occurrence in Moravia in the Czech Republic. The name is derived from the Greek {{transl|grc|stilpnos}} for shining, and {{transl|grc|melanos}} for black.