MARGARITE



Margarite is a calcium aluminum silicate hydroxide mineral of the brittle mica group.
Margarite was described by Cook (1973) and Dunn and Frondel (1990) from an occurrence in the marble very near the Sterling Hill orebody, but was known locally before then; some specimens were mislabeled as muscovite, mariposite, or kyanite. An early report in the local journal, The Picking Table, referred to a fuchsite from Franklin; this may have been margarite as well. Another occurrence of margarite was investigated by Yau et al. (1984).
Margarite from the principal occurrences given herein occurs in crystals up to 3 cm; they are pseudohexagonal in habit. Sterling Hill margarite is light bluish-green to light greenish-blue; colorless material is known and is white in the aggregate. It has a pearly luster, which is sometimes distinctive; perfect {001} cleavage; and a density of 3.03 g/cm3; physically deformed material is common. The fluorescence is pale yellow in both shortwave and longwave ultraviolet. It is distinguished from muscovite by its brittleness.
Although margarite is not known to be common locally, colorless masses may have been overlooked. Margarite was found in the Franklin Marble, immediately adjacent to the Sterling Hill orebody, and specimens were brought out through Sterling Hill mining adits. Hence, specimens are commonly labeled "Sterling Hill," this implying an incorrect orebody occurrence. The occurrence was approximately 12 meters from the orebody, on the 340 and 430 levels, and was locally abundant. This bluish-green margarite is in a bright-white calcite matrix, associated with 1-2 cm crystals of red corundum. The combination is very esthetic, and this fact may have ensured the preservation of much material. A host of other minerals are present, including but not limited to anorthite, gahnite, hercynite, arsenopyrite, graphite, titanite, phlogopite, clinochlore, rutile, zircon, and very rare minerals such as goldmanite and thortveitite (Dunn and Frondel, 1990).
Another notable occurrence was found about a kilometer distant in the Franklin Quarry in Franklin, in 1982, and was studied by Yau et al. (1984). The assemblage is simpler, having no corundum and none of the rarest minerals. Here, margarite is associated with calcite, dolomite, titanite, rutile, muscovite, phlogopite, and clinochlore. This is interpreted as a retrograde assemblage; the parent rock is assumed to have been composed of feldspars and/or scapolites. The data indicate an assemblage in which phlogopite is replaced by chlorite at 370-450° C at an assumed pressure of 2 kilobars.
A specimen from Franklin in the Smithsonian Institution consists of massive, white-to-colorless margarite enclosing 1-2 cm uvite crystals. Additional occurrences have been found in the Franklin Marble between the Franklin and Sterling Hill deposits. (Dunn, 1995)

 Location Found: Franklin and Ogdensburg
     
 
 Year Discovered: 1820
     
 Formula: CaAl2(Al2Si2O10)(OH)2
 Essential Elements: Aluminum, Calcium, Hydrogen, Oxygen, Silicon
 All Elements in Formula: Aluminum, Calcium, Hydrogen, Oxygen, Silicon
     
 IMA Status: Approved
     
Fluorescent Mineral Properties
 Shortwave UV light: Weak white, gray
 Mid wave UV light: Weak white, gray
 Longwave UV light: Weak white, gray
     
 To find out more about this mineral at minDat's website, follow this link   Margarite

     
 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.469

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.67
The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 58, No. 1 - Spring 2017, pg. 12Fluorescent Minerals of Franklin and Sterling Hill, N.J., Part 2, Richard C. Bostwick - Margarite
View IssueV. 33, No. 2 - Fall 1992, pg. 11The Check List of Franklin-Sterling Hill Fluorescent Minerals - Margarite (Fluorescent Info)
View IssueV. 32, No. 1 - Spring 1991, pg. 9An Uncommon Margarite/Corundum Assemblage From Sterling Hill, New Jersey, Pete J. Dunn, Clifford Frondel, Margarite
View IssueV. 27 No. 2 - Fall 1986, pg. 6Minerals of the Franklin Quarry, Philip P. Betancourt, Margarite
View IssueV. 18, No. 2 - September 1977, pg. 15The Fluorescent Minerals of Franklin and Sterling Hill, NJ by Richard C. Bostwick - Margarite
     
Images
     
Margarite, calcite, corundum crystals, rutile and minor pyrite from the Sterling Hill Mine, Ogdensburg, NJMargarite, calcite, corundum crystals, rutile and minor pyrite from the Sterling Hill Mine, Ogdensburg, NJ under longwave UV Light
Margarite (blue-green plates), calcite (white), corundum crystals (purple), rutile (black) and minor pyrite (gold) from the Sterling Hill Mine, Ogdensburg, NJ. Field of view 2". From the collection of, and photo by Robert A. Boymistruk.
Margarite, calcite, corundum crystals, rutile and minor pyrite from the Sterling Hill Mine, Ogdensburg, NJ under longwave UV light. The margarite fluoresces weak gray-blue, corundum red, the calcite, rutile and pyrite are non-fluorescent. Field of view 2". From the collection of, and photo by Robert A. Boymistruk.

Margarite crystal sprays in franklin marble from the Franklin Quarry, Franklin, NJMargarite crystal sprays in franklin marble from the Franklin Quarry, Franklin, NJ under shortwave UV Light
Margarite crystal sprays (blue-green) in franklin marble from the Franklin Quarry, Franklin, NJ. Field of view 1". From the collection of, and photo by JVF.
Margarite crystal sprays in franklin marble from the Franklin Quarry, Franklin, NJ under shortwave UV light. The margarite fluoresces dull blue-white and the franklin marble is non-fluorescent. Field of view 1". From the collection of, and photo by JVF.






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