Muscovite, a potassium aluminum silicate hydroxide mineral of the mica group, is a minor mineral locally, but occurs widely distributed. It was reported from the Franklin Marble in greenish platy masses by Palache (1935) and also by Yau et al. (1984). It was reported from the calcium-silicate units of the Franklin orebody, the local gneisses, and pegmatites by Frondel (1972), and from the Buckwheat Dolomite by Peters et al. (1983). It was reported from Sterling Hill by Frondel (1972). It comprises part of the pseudomorphous "crystals" known locally as algerite (Hunt, 1849), an altered scapolite. Energy-dispersive analysis shows only K, Al, and Si. Muscovite may be more common than recognized to date, particularly in feldspar- and scapolite-bearing assemblages, as colorless, platy crystals with perfect cleavage.
The only muscovite from the Franklin orebody which is noteworthy or distinctive is a barian muscovite, originally described by Bauer and Berman (1933) and to which they applied the name bariummuscovite; some specimens improperly have been called oellacherite by collectors. This material was re-examined by Heinrich and Levinson (1955) who noted that it formed as an alteration of a feldspar, provided X-ray powder data, and stated that this was the 1M polytype.
This barian muscovite is unlike common micas in its physical appearance: it is fine-grained; cleavage is not evident; the color is a deep violet-pink; and it has a dull grainy luster. It occurs in 5-10 cm masses and is associated with an unanalyzed mica, andradite, and copper. Bauer and Berman (1933) reported an association with microcline. This material was re-examined by Dunn (1984), who noted the presence of both hyalophane and abundant barite inclusions, and found a much lower barium content than published by Bauer and Berman (1933); the new values for BaO and K2O are nearly the reverse of those given earlier. Nothing is known of its geologic occurrence. (Dunn, 1995)

 Location Found: Franklin and Ogdensburg
 Formula: KAl2(AlSi3O10)(OH)2
 Essential Elements: Aluminum, Hydrogen, Oxygen, Potassium, Silicon
 All Elements in Formula: Aluminum, Hydrogen, Oxygen, Potassium, 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   Muscovite

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.465

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.69

The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 27 No. 2 - Fall 1986, pg. 7Minerals of the Franklin Quarry, Philip P. Betancourt, Muscovite
View IssueV. 26, Combined Issue 1985, pg. 11Mineral Notes Research Reports, Barian Muscovite
View IssueV. 24 No. 2 - Fall 1983, pg. 15Minerals of the Buckwheat Dolomite Franklin, New Jersey, Muscovite (small description)

Barian muscovite, andradite garnet, hyalophane and barite from Franklin, NJ.
Barian muscovite (violet-pink), andradite garnet (brown), hyalophane (white) and minor barite (white) from Franklin, NJ. Field of view 2". From the collection of, and photo by Robert A. Boymistruk.

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