Manganese-hoernesite (Manganohörnesite), a manganese arsenate hydrate mineral, was listed from Sterling Hill by Parker and Troy (1982) and was verified by [Dunn]. It has not been found at Franklin. Manganese-hoernesite occurs as colorless to white, distinctly lath-like, 1-2 mm crystals with a decidedly pearly luster; smaller crystals appear fibrous. Most crystals are bent or twisted; some crystals form aggregates and may form part of a breccia cement. Energy-dispersive X-ray analysis indicated only Mn and As as major constituents, with traces of Zn; no other data exist.
Manganese-hoernesite is found associated with adelite, alleghanyite, and kraisslite on red-willemite ore. The mineral is poorly named; it is related to bobbierite, not to hoernesite. X-ray methods are best used for verification. (Dunn, 1995)

 Location Found: Ogdensburg
 Year Discovered: 1854
 Formula: (Mn,Mg)3(AsO4)2 · 8H2O
 Essential Elements: Arsenic, Hydrogen, Manganese, Oxygen
 All Elements in Formula: Arsenic, Hydrogen, Magnesium, 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   Manganohörnesite

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.673. 'Manganese-hoernesite'

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