Stilpnomelane

Compare "chalcodite". May be confused with "biotite" and other brownish mica (e.g. annite), also with dark chlorite.

History

Activities related to discovery and approval of the group members

Structural context

Stilpnomelane
Crystal System triclinicCrystal Class pinacoidalSpace Group P-1
a21.899—22.2 (22.0118)
b21.886—22.2 (22.0128)
c17.609—17.835 (17.7063)
alpha124.61—125.03 (124.79)
beta95.98—96.07 (96.025)
gamma119.955—120 (119.9713)
volume5033.852—5199.1 (5104.8143)

Based on 4 measurements

Chemical context

Stoichiometric formulas

Stilpnomelane
mindat.org
  • March 13, 2023(K,Ca,Na)(Fe,Mg,Al)8(Si,Al)12(O,OH)36·nH2OThe ratio of ferric vs. ferrous iron varies greatly. An ideal end-member "ferrostilpnomelane" can be represented by K5Fe482+(Si63Al9)O165(OH)48.12H2O. An ideal end-member "ferristilpnomelane" (which is thought to result from oxidation after primary crystallization) can be represented by K5Fe483+(Si63Al9)O216.36H2O. Note that neither end-member composition has been reported yet.
IMA
  • March 13, 2023(K,Ca,Na)(Fe,Mg,Al)8(Si,Al)12(O,OH)36 · nH2O
mineralogy.rocks
  • Aug. 30, 2022(K,Ca,Na)(Fe2+,Mg,Al,Fe3+)8(Si,Al)12(O,OH)36·nH2O

Elements recorded on EPMA

1
Fe
1
O
1
Si

Physical properties

ColorColor entities, recognized using a custom trained NER model
    • dark reddish brown
    • golden brown
      • dark green
      Color noteOriginal color note from the source
      Red, brown, black, dark green, dark reddish brown, golden brown
      StreakStreak entities, recognized using a custom trained NER model
          Streak noteOriginal streak note from the source
          White, grey
          Lustre
          Sub-Vitreous
          Pearly
          Sub-Metallic
          Fracture
          Micaceous
          Transparency
          Translucent
          Hardness
          3—4
          Measured density
          2.59—2.96
          Calculated density
          2.667