Mineral Information and Data:

Julgoldite-(Fe3+)
Ca2Fe3+Fe3+2(Si2O7)(SiO4)O(OH) • H2O [CNMNC approved formula]

Named as the Fe3+ predominant julgoldite. Species named for Julian Royce Goldsmith (1918-1999), American geochemist, University of Chicago. First published in 1971. Renamed per nomenclature of pumpellyites and julgoldites (IMA approved, 1973). Species defined as distinct from julgoldite-(Fe2+).

IMA status : Renamed IMA Approved; 1973 (IMA1972-003)
CLASSIFICATION 
Dana
(8th edition) :
58.02.02.02  
  (58) Sorosilicate Insular, Mixed, Single, and Larger Tetrahedral Groups
  (58.02) with cations in [6] and higher coordination; single and double groups (n=1,2)
  (58.02.02) Pumpellyite group
  
Nickel-Strunz
(10th edition) :
09.BG.20
  (09) Silicates
  (09.B) Sorosilicates (dimer) structures
  (09.BG) Sorosilicates with mixed SiO4 and Si2O7 groups; cations in octahedral [6] and greater coordination
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Space group: P2/m
Unit cell: a = 8.922(4)Å, b = 6.081(3)Å, c =19.432(9)Å, β = 97:60(6)°, Z=4
Crystal Habit: Crystals flat prismatic to bladed, to 2 mm, elongated along [010] and flattened || {100}. In fan-shaped, plumose crystal groups; granular.
Twinning: Twin plane {001}, typically repeated, common
  
Color: Deep black, greenish black to green in small fragments; in thin section, brilliant interference colors in greens or blues
Diaphaneity: Transparent
Luster: Nearly submetallic
Hardness (Mohs): 4.5
Measured Density: 3.58 - 3.60 g/cm3
Cleavage: Perfect on {100} and {001}
Tenacity: Brittle
Streak: Greenish-olive with a bluish tinge
  
Polymorphism and Series: Forms two series, with pumpellyite-(Fe3+); and with pumpellyite-(Mg)
Geologic Setting: Occurs fiIling cavities and embedded in large plates of apophyllite and minor barite, which constitute a fissure filling in granular hematite-magnetite ore from the "Amerika" stope (Langban, Sweden).
Mineral Association: Apophyllite, barite, hematite, magnetite, ilvaite, calcite, quartz, chlorite, prehnite, epistilbite, stilbite, pectolite, laumontite, babingtonite, titanite
  
Comments: Insoluble in cold (1+1 l)HCl, rapidly dissolved by hot (1+1)HCl giving a gel.
See: Passaglia E, Gottardi G (1973) Crystal chemistry and nomenclature of pumpellyites and julgoldites, The Canadian Mineralogist 12, 219-223

 

Julgoldite-(Fe3+)
Dark gray metallic massive julgoldite-(Fe3+)
associated with hematite, andradite and rhodonite.
Origin: Harstigen Mine, Pajsberg, Filipstad, Varmland, Sweden.
Photo: © RRUFF Project

 

Julgoldite-(Fe3+)
(zoom-in of above)

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