Hedenbergite



Hedenbergite is a calcium iron silicate mineral of the pyroxene group and the Fe-analogue of diopside. Hedenbergite from both Franklin and Sterling Hill is highly magnesian; most samples have intermediate compositions in solid solution to diopside. Solid solution toward johannsenite or petedunnite is quite limited locally. Hedenbergite associated with magnetite at Balls Hill in Franklin approximates to Ca(Fe0.58Mg0.36Mn0.06)Si2O6 in composition. That described in 4 analyses from Sterling Hill by Reilly (1983) approximates 85 mole % of the end-member.
Hedenbergite is found at both Franklin and Sterling Hill, but is an uncommon mineral at both localities, being restricted to a few anomalous assemblages, in keeping with the dominant Mn/Mg local solid solution and the paucity of iron silicates.
Hedenbergite is massive; well-formed crystals are uncommon or unknown. In the dominant Franklin assemblage, noted below, hedenbergite is dark green, visually black, with imperfect cleavage and vitreous luster. Its optical properties have not been determined.
The predominant and most abundant hedenbergite occurrence is at Franklin, where it occurs as dark green intergrowths with epidote; it is described under fluorapophyllite (Betancourt, 1989). This assemblage has been well preserved in systematic collections, in large part due to the presence of large euhedral fluorapophyllite crystals, together with euhedral crystals of epidote, zircon, ferroaxinite, pyrite, andradite, and natrolite. Another Franklin occurrence, albeit a rare one, consists of dark green prismatic crystals within Franklin ferristilpnomelane (Dunn et al., 1984b); these crystals approach 80 mole % of the end-member.
At Sterling Hill, hedenbergite occurs in several assemblages. It was found on the 1600 level, associated with feldspar, epidote, and quartz. It also was found on the hanging wall of the black-willemite zone, on the 430 level, associated with molybdenite, powellite, calcite, and feldspar. Johnson (1990) reported it from the 340 level. Hedenbergite was found in an assemblage of calcite, franklinite, ferroactinolite, and andradite from drill-hole #124, 119 feet from its origin on the 340 level, surrounded by andradite and altering to cummingtonite and ferroactinolite (Reilly, 1983). See also the comments of Jenkins (1994). (Dunn, 1995)


 Location Found: Franklin
     
 
 Year Discovered: 1819
     
 Formula: CaFe2+Si2O6
 Essential Elements: Calcium, Iron, Oxygen, Silicon
 All Elements in Formula: Calcium, Iron, Oxygen, Silicon
     
 IMA Status: Approved
     
     
 To find out more about this mineral at minDat's website, follow this link   Hedenbergite

     
 References:
Dunn, Pete J. (1995). Franklin and Sterling Hill New Jersey: the world's most magnificent mineral deposits. Franklin, NJ.: The Franklin-Ogdensburg Mineralogical Society. p.434


The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 41, No. 1 - Spring 2000, pg. 13A Scheelite-bearing Assemblage From Franklin, New Jersey By Robert E. Jenkins II - Hedenbergite
View IssueV. 35, No. 1 - Spring 1994, pg. 22Geology and Mineralogy of a Veinlet Assemblage Associated With Wollastonite-Bearing Rocks, Sterling Mine, Ogdensburg, New Jersey, Robert E. Jenkins II - Hedenbergite
View IssueV. 30, No. 1 - Spring 1989, pg. 9The Epidote-Pyroxene-Fluorapophyllite Assemblage in the Franklin Mine at Franklin, New Jersey, Philip P. Betancourt, Hedenbergite (small description)
     
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