Friedelite



Friedelite is a manganese silicate hydroxide chloride mineral of the friedelite group. Chlorine may be absent, however, as noted by Palache (1935). There is extensive solid solution between Mn8Si6O15(OH)9Cl and Mn8Si6O15(OH)9(OH), as demonstrated by Dunn et al. (1981), but there is no nomenclatural distinction. In general, solid solution of Mg, Fe, and Zn, for Mn is very limited (Dunn and Peacor, 1981c), but the late Dr. Jun Ito analyzed one massive dark brown friedelite, associated with radiating willemite, and found 5.2 wt. % MgO and 2.7 wt. % ZnO. The relations between Cl- and (OH)-bearing material have not been studied in detail.
Friedelite from Franklin has a lengthy history. It was first reported from here by Palache (1910). Comparisons with schallerite were made by Gage et al. (1925) and Bauer and Berman (1928), and Hey (1956) provided new data and discussed the group relations. The group was further expanded, and more insights into friedelite provided, by Frondel and Bauer (1953) in their description of manganpyrosmalite. Additional X-ray powder data were provided by Heubner (1967) and Peacor and Essene (1980).
Crystal-chemical data for friedelite, schallerite, and caryopilite were provided by Dunn et al. (1981c), and they showed the existence of solid solutions between possible Cl- and (OH) end-members of friedelite from both Franklin and Sterling Hill. Ozawa et al. (1983) studied the layer structure of friedelite relative to that of mcGillite. Fine specimens have been found at both localities (Foshag, 1920) and have been available for over 75 years.
Friedelite occurs as crystals to 4 mm, as partially described by Palache (1935); those found in subsequent years are of markedly similar morphology, and many are hemimorphic. Fine crystals are known from both deposits and commonly occur in subparallel growth normal to vein surfaces. Aside from these common single-crystal habits, friedelite also occurs as platy aggregates on Franklin willemite crystals. The preponderance of local material is massive, occurring in veins and seams in the ore. It is fine-grained; some is similar to some serpentines in texture and habit. Friedelite is pink, red, reddish-orange, or dark brown; the bulk of the material is reddish-brown; and yellow material is rare. Cleavage is perfect and is observed in free-growing crystals and sometimes in coarsely-crystallized aggregates. The luster is generally vitreous, but some cleavages are pearly. The surface of some broken fine-grained vein material is similar to that of chert or quartzite. The density is 3.05 g/cm3.There is no discernible fluorescence in ultraviolet.
Massive friedelite is easily confused with a number of species which may form similar aggregates in vein assemblages. It is distinguished from reddish willemite by its lack of fluorescence and from sphalerite by sphalerite's inferior hardness, resinous luster, and odor of sulfur when broken or intensely scratched. Distinguishing friedelite from the closely related manganpyrosmalite, nelenite, and schallerite is difficult and should be done employing both X-ray and optical methods.
Friedelite is a moderately common secondary mineral at both Franklin and Sterling Hill and is the most abundant OH-bearing secondary Mn-silicate here. Superb crystals are commonly associated with calcite or barite, less commonly with secondary willemite; friedelite has been reported once with oxidized sulfides (Jenkins and Misiur, 1994). Palache (1910, 1935) noted a number of assemblages; there are many more.
The preponderance of local material is present as veins, some of which are centimeters in thickness, in franklinite-willemite ore which is commonly calcite-bearing. Although such veins may be vuggy and yield crystals or crystal-druse surfaces, the majority of veins are composed of tight, dense, fine-grained, microcrystalline aggregates. These may be layered, or may be uniform and homogeneous in color and texture. The best massive friedelite, from homogeneous veins up to 5 cm thick and occurring in varying shades of red, has provided some gem material for the cutting of
cabochons (Webster, 1975).
Friedelite veins are commonly, but not exclusively, monomineralic. Unlike most local vein minerals, friedelite commonly occurs without willemite. Friedelite veins exhibit many of the same features shown by willemite or serpentine veins. Indeed, friedelite is responsive to Mn-silicate concentrations in much the same way that secondary serpentine is to Mg-silicate concentrations, and friedelite occupies the mineralogic niche commonly held by serpentine in Mg-rich assemblages, such as at Sterling Hill.
Friedelite is not always pure; physical mixtures with other minerals, most notably with schallerite and manganpyrosmalite, are not uncommon. These occur in late-stage fracture fillings and breccia cements, such as one hosting franklinite, andradite, and microcline. Arsenian friedelites have been reported (Bauer and Berman, 1928), but have not been subjected to detailed modern studies. [Dunn] considers it probable that these are physical mixtures of friedelite with other arsenic-bearing minerals, possibly nelenite; the detection of such a mixture by X-ray powder methods is almost impossible; the powder patterns are nearly identical. Another possibility for arsenic contamination is a mixture of friedelite with the unnamed arsenite analogue of friedelite (Peacor et al., 1986), not yet known to occur locally. Such mixtures, at least on a small scale, might be more common than recognized and may provide a ready host for minor arsenic in some silicate assemblages. (Dunn, 1995)


 Location Found: Franklin and Ogdensburg
     
 
 Year Discovered: 1876
     
 Formula: (Mn,Fe)8Si6O15(OH,Cl)10
 Essential Elements: Hydrogen, Manganese, Oxygen, Silicon
 All Elements in Formula: Chlorine, Hydrogen, Iron, Manganese, Oxygen, Silicon
     
 IMA Status: Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
     
     
 To find out more about this mineral at minDat's website, follow this link   Friedelite

     
 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.475

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.57


The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 35, No. 2 - Fall 1994, pg. 21A Complex Base-Metal Assemblage From the Sterling Mine New Jersey - Friedelite
View IssueV. 34, No. 1 - Spring 1993, pg. 13The Flinktie / Cahntie / Jarosewichite Assemblage From Franklin, New Jersey, Vandall T. King - Friedelite
View IssueV. 29, No. 2 - Fall 1988, pg. 14Mineral Notes Research Reports, Friedelite
View IssueV. 23, No. 1 - Spring 1982, pg. 10Mineral Notes Research Reports, Relationship Between McGillite and Friedelite
View IssueV. 23, No. 1 - Spring 1982, pg. 11Additional Information on Schallerite and Friedelite and Caryopilite, Pete J. Dunn
View IssueV. 19, No. 2 - September 1978, pg. 5Recent Mineral Occurrences at Sterling Hill by Stephen Sanford - Friedelite (small article)
View IssueV. 10, No. 2 - August 1969, pg. 9Mineral Notes - Friedelite
View IssueV. 7, No. 2 - August 1966, pg. 8The Minerals of Sterling Hill 1962-65 by Frank Z. Edwards - Friedelite
     
Images

     
Vein of massive brown friedelite in willemite, calcite, franklinite, Sterling Hill Mine
Vein of massive brown friedelite in willemite / calcite / franklinite ore from Sterling Hill, New Jersey. Photo by JVF



Friedelite vein (gemmy), calcite and franklinite from Sterling Hill Mine, NJ.
Friedelite vein (gemmy red to pink), calcite (white) and franklinite (black) from Sterling Hill Mine, NJ. From the collection of, and photo by Robert A. Boymistruk.


Friedelite, green willemite and serpentine from Franklin, NJFriedelite, green willemite and serpentine from Franklin, NJ under shortwave UV Light
Friedelite (pinkish-orange), willemite (mint green) and serpentine (brown) from Franklin, NJ. From the collection of, and photo by Robert A. Boymistruk.
Friedelite, willemite and serpentine from Franklin, NJ under shortwave UV light. The willemite fluoresces green, the friedelite and serpentine are non-fluorescent. From the collection of, and photo by Robert A. Boymistruk.


Friedelite crystals on calcite, franklinite matrix from Sterling Hill Mine, Ogdensburg, NJ
Friedelite crystals (light brown) on calcite, franklinite matrix from Sterling Hill Mine, Ogdensburg, NJ. 2" x 2". From the collection of Zack and Ralph Bonard, photo by WP.







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