Mcgovernite is a complex ferric-iron magnesium manganese zinc arsenite arsenate silicate hydroxide mineral. As shown by Dunn and Nelen (1980), the composition of mcgovernite, like that of kraisslite, is remarkably constant from specimen to specimen. The similarity in chemical constituents supports the close relation between these species, and the presence of ferric iron in both mcgovernite and kraisslite may further support the relation to hematolite and similar phases. Although both minerals have As in two oxidation states, the ratio of As3+:As5+ is different. There is no definitive chemical formula for mcgovernite; the structure is unknown. Mcgovernite was described by Palache and Bauer (1927b) from Sterling Hill. They recognized its complex chemical nature and did not propose a precise chemical formula. The possible relation of mcgovernite to dixenite was pointed out by Bauer and Berman (1928). The crystallography of mcgovernite was studied by Wuensch (1960), who also discussed relations with dixenite and who subsequently (1968) compared the crystallography of these phases. Moore and Araki (1978) discussed the relations in the hematolite group and provided the formula M2+19Zn3(OH)21(AsO3)(AsO4)3(SiO4)3. The chemical composition of mcgovernite was considered as part of a study of kraisslite by Dunn and Nelen (1980). They verified the original ratio of Bauer (for As3+:As5+) and provided new chemical data. Mcgovernite is not known from Franklin.
Mcgovernite occurs as platy hexagonal crystals identical to those of kraisslite. Visually, the two minerals can be nearly indistinguishable. On some specimens, mcgovernite occurs as large (6 cm) radial flattened sprays and splayed rosettes, a habit not seen to date in kraisslite. Mcgovernite is reddish-brown and is visually similar to kraisslite in luster and most aspects. The density is 3.719 g/cm3 (Palache and Bauer, 1927). Mcgovernite is distinguished easily from kraisslite by its index of refraction and X-ray powder pattern. There is no discernible response to ultraviolet.
Mcgovernite was found in 1927 on the 900 level at Sterling Hill. It remained a relatively uncommon mineral, but was found again in the early 1980's. The earlier material occurred as a massive vein filling, sometimes having a breccia texture, and as splayed rosettes, some browner than others, on fracture and vein surfaces. It was somewhat notable for having few associated arsenate species, unlike kraisslite which occurs with many such minerals. The later find of mcgovernite provided material of lesser richness, but some of it was vuggy, and secondary hodgkinsonite was found in mcgovernite-lined vugs. (Dunn, 1995)

 Location Found: Ogdensburg (Type Locality), unique to Franklin/Ogdensburg area
 Mineral Note: Mcgovernite can be distinguished from kraisslite by its lighter color and crystal sprays.
 Year Discovered: 1927
 Formula: Mn19Zn3(AsO4)3(AsO3)(SiO4)3(OH)21
 Essential Elements: Arsenic, Hydrogen, Manganese, Oxygen, Silicon, Zinc
 All Elements in Formula: Arsenic, Hydrogen, Manganese, Oxygen, Silicon, Zinc
 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   Mcgovernite

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.500

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
V. 59, No. 2 - Fall 2018, pg. 18Hydrothermal Mineral Deposition in a Rock-Dominated Fluid System at Sterling Hill, New Jersey - Mcgovernite and zincite
View IssueV. 34, No. 2 - Fall 1993, pg. 16Recent Mineral Finds From The Sterling Mine Ogdensburg, New Jersey - Mcgovernite
View IssueV. 29, No. 2 - Fall 1988, pg. 3Notes from the Laboratory & Changes to the List of Species From Franklin and Sterling Hill, Pete J. Dunn, John L. Baum, New Formula, Mcgovernite
View IssueV. 22, No. 2 - September 1981, pg. 7Mineral Notes Research Reports, Kraisslite and Mcgovernite
View IssueV. 9, No. 1 - February 1968, pg. 15The Exclusive Minerals of Franklin/Ogdensburg, N.J. (as of January 1968) by Frank Z. Edwards - McGovernite (Short Note)
View IssueV. 2, No. 1 - February 1961, pg. 5Mcgovernite and Dixenite (small article)

Mcgovernite mineral coating on calcite, zincite and franklinite from Sterling Hill, NJ.
Mcgovernite mineral coating on calcite (white), zincite (red) and franklinite (black) from Sterling Hill, NJ. Photo by JVF.

Mcgovernite sprays, calcite, franklinite and willemite from Sterling Hill, NJ.
Mcgovernite (brassy sprays), calcite (white), franklinite (black) and willemite (peach) from Sterling Hill, NJ. From the collection of, and photo by Robert A. Boymistruk.

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