The oxide and hydroxide minerals are very important at Franklin and Sterling Hill, and the predominance of two oxide minerals is one of the significant features of the deposits. Among the oxides of the principal metals (Zn,Mn,Fe), only zincite and franklinite play an economic role; these minerals are, together with willemite, the dominant ore minerals.
There are few oxides and hydroxides of zinc found locally; zincite, zinc oxide, is locally abundant, although exceedingly rare elsewhere.
Manganese oxides are not common in general. Manganese oxide, manganosite, was locally abundant in at least one Franklin occurrence but was generally quite rare. Pyrochroite and cianciulliite are the only secondary, divalent manganese oxides found locally. With the exception of hetaerolite, a Zn-Mn3+ oxide species widespread in small amounts, other trivalent Mn species, such as groutite, feitknechtite, hausmannite, and manganite, are rare and are found at Franklin. Secondary, hydrated Mn4+ oxide species, such as aurorite, birnessite, chalcophanite, todorokite, and woodruffite, together with Mn3+-bearing hetaerolite, are in part moderately common at Sterling Hill but are mostly restricted to an anomalous and deeply weathered saprolite, the “mud-zone.”
The principal iron oxides are franklinite, magnetite, and hematite. Franklinite is predominant by far, and magnetite is next in abundance. Hematite occurrences, aside from alterations of franklinite and magnetite, are highly localized and of no economic significance.
In the descriptive sections which follow, zincite is discussed first and the spinel group, containing franklinite, second. The other oxide minerals are presented in alphabetical order.
The locally occurring oxide minerals are listed below.
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This page created: January 13, 2001