Manganosite is a manganese oxide mineral. Local material is quite near end-member composition. Palache (1935) reported Bauer's analysis of material with zincite impurities as having 4.89 wt. % ZnO, but McSween (1976) reported only 2.22 wt. % by use of an electron microprobe.
Manganosite was first described from Franklin by Palache (1910) and has not been found at Sterling Hill. A second occurrence was reported from the northern end of the mine by Palache (1935), who also gave the optical data of Ford (1914). Franklin material was studied using X-ray methods by Levi (1924) and Berry and Thompson (1962).
Franklin manganosite occurs as massive material, intimately associated with zincite. Euhedral crystals are unknown, but octahedral fragments, separated along parting planes by zincite, are commonly 1 cm in size and occur up to 10 cm. Manganosite is a rich dark green, easily oxidized, and most specimens appear black. Cleavage is cubic, the luster is vitreous to adamantine (dull after exposure), and the density is 5.36 g/cm3.
The predominant descriptive characteristic of Franklin manganosite is the very evident mutual exsolution of manganosite in zincite and zincite in manganosite. The minerals break among parting planes, and thus many extant specimens have planar features resembling crystal faces. Ramdohr (1938) had noted the presence of a hausmannite-hetaerolite rim on some manganosite grains. Studies by [Dunn] confirm Ramdohr's and McSween's (1976) findings that this is hausmannite, although McSween found Mn2+:Zn to be 1:1. The zincite-manganosite exsolution was studied in detail by Frondel (1940), who found zincite parallel to manganosite.
Most manganosite is associated with jacobsite, zincite, and calcite. Olivine-group minerals and related minerals (tephroite, leucophoenicite, and sonolite) are also associated. Of these, leucophoenicite and sonolite are the most common. The known specimens are almost entirely from the above-described assemblage. In addition, manganosite is rarely known as thin films on black hetaerolite which occurs as common exsolutions from zincite; one such specimen has manganosite associated with abundant manganhumite. (Dunn, 1995)

 Location Found: Franklin
 Year Discovered: 1817
 Formula: MnO
 Essential Elements: Manganese, Oxygen
 All Elements in Formula: Manganese, Oxygen
 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   Manganosite

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.600

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. 32, No. 1 - Spring 1991, pg. 15Mineral Notes, Research Reports, Manganese-Rich Ore Assemblages, Manganosite (small description)
View IssueV. 15, No. 2 - August 1974, pg. 8Fluorescent Corner - Margarosanite
View IssueV. 10, No. 2 - August 1969, pg. 11Mineral Notes - Rhodochrosite/Manganosite

Manganosite, foliated zincite and sonolite from Franklin, NJ
Manganosite (dark green), foliated zincite (dark red) and sonolite (pink brown) from Franklin, NJ. 3 3/4" x 2 3/8". From the collection of, and photo by Robert A. Boymistruk.

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