Julgoldite

A variety of Minerals

What is Julgoldite?

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. Julgoldites, along with more common minerals like epidote and vesuvianite, belong to the subclass of sorosilicates, the rock-forming minerals that contain SiO4 tetrahedra that share a common oxygen to form Si2O7 ions with a charge of 6- (Deer et al., 1996). Julgoldite has been recognized for its importance in low grade metamorphism, forming under shear stress accompanied by relatively low temperatures (Coombs, 1953). Julgoldite was named in honor of Professor Julian Royce Goldsmith (1918–1999) of the University of Chicago.

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Julgoldite Localities Map

See where Julgoldite is found with a localities map, collecting zones, and geology context. Generate a sample map preview below.

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North ZoneCentral RidgeSouth Basin

Key Characteristics

Characteristics of Julgoldite

Moore (1971) sampled flat prismatic or bladed crystals, with the greatest dimension of each mineral to be no more than 2mm. The julgoldites found in the basalt cavities in India were almost 10 mm in length (Wise and Moller, 1990). Julgoldite is elongated parallel b [010] and flattened parallel a {100} (Moore, 1971). Allman and Donnay (1973) calculated the cell dimensions to be a 8.922(4), b 6.081(3), c 19.432 (9) Å. 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} (Moore, 1971). It has a greenish-olive powdery streak with a blue tinge (Moore, 1971). Under the petrographic microscope, a thin section of the mineral will display brilliant interference figures in greens or blues (Moore, 1971). The mineral is classified under the space group A2/m (Moore, 1971). A monoclinic mineral, julgoldite is isostructural to pumpellyite and epidote (Allman and Donnay, 1973).

Composition of Julgoldite

The chemical formula of julgoldite is (Ca,Mn)2(Fe,Fe,Mg)(Fe,Al)2(SiO4)(Si2O7)(OH)2·(H2O) (Moore, 1971). Pumpellyites are classified according to the prevailing metals in the X and Y sites (Moore, 1971). When Mg in the X position and Al in the Y position and both occupy greater than 50% molarity of their positions, then the mineral is identified as a pumpellyite (Moore, 1971). Julgoldites are identified when Fe in the X and Fe in the Y each occupy greater than 50% molarity of their positions (Moore, 1971).