Julgoldite: Properties and Occurrences

Julgoldite is a member of the pumpellyite mineral series, a series of minerals characterized by the chemical bonding of silica tetrahedra with alkali and transition metal cations. It is a particular pumpellyite mineral. It has been recognized for its importance in low-grade metamorphism, forming under shear stress accompanied by relatively low temperatures.

Julgoldite was named in honor of Professor Julian Royce Goldsmith (1918–1999) of the University of Chicago.

General Information

  • Category: Sorosilicates
  • Formula: (Ca,Mn)2(Fe2+,Fe3+,Mg)(Fe3+,Al)2(SiO4)(Si2O7)(OH)2(H2O)
  • Crystal system: Monoclinic (Julgoldite-(Mg) unknown)
  • Crystal class: Prismatic (2/m) (same H-M symbol)

Fig: Julgoldite

Properties

The color of julgoldite is usually a deep lustrous black, and it has a hardness of 4.5 and cleavage on the a-axis {100}. It has a greenish-olive powdery streak with a blue tinge. Under the petrographic microscope, a thin section of the mineral will display brilliant interference figures in greens or blues. The mineral is classified under the space group A2/m.

  • Color: Black to greenish olive
  • Crystal habit: blades or prisms.
  • Cleavage: [100] Good
  • Mohs scale hardness: 4.5
  • Luster: sub-metallic
  • Streak: greenish olive
  • Specific gravity: 3.6
  • Optical properties: Biaxial (-)
  • Fusibility: loses water

Occurrence

Julgoldite were first collected as samples entrenched in large plates of apophyllite and barite, comprising a fissure inside granular hematite-magnetite ore in Långban, Sweden. Julgoldite has since been discovered in other parts of the world: Edinburgh, Scotland, and Norilsk, Taymyr Peninsula, Russia, one of the largest nickel deposits in the world, in metamorphosed basalts and databases associated with prehnite and laumontite. Julgoldite has also been found exposed in basalt cavities in the Kandivali Quarry near Bombay, India along with other silicates, including pumpellyite- Fe2+, ilvaite, babingtonite, hydro andradite, prehnite, and chlorite.

Association: Apophyllite, barite, hematite, magnetite, ilvaite, calcite, quartz, chlorite, prehnite, epistilbite, stilbite, pectolite, laumontite, babingtonite, titanite.

 

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