This sample of franklinite, (Zn,Fe,Mn)(Fe,Mn)2O4 (zinc iron manganese oxide), is about 13 cm in diameter. It is very heavy due to the presence of magnetite, whi — Photo: Nessa Eull · CC0
Franklinite
A zinc-iron spinel found almost exclusively at Franklin and Sterling Hill, New Jersey — an important zinc ore there.
Intro adapted from Wikipedia (CC BY-SA).
Franklinite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula ZnFe³⁺₂O₄.
It crystallizes in the cubic crystal system (space group Fd3m). It is a member of the Spinel structural group.
Key properties: Mohs hardness 5.5–6.5; specific gravity 5.05–5.22; typically black; Reddish brown to black streak; Metallic to semimetallic; may be dull luster.
IMA symbol Frk, grandfathered status — known before the IMA’s founding, named in 1819.
Found in beds and veins formed by high-temperature metamorphism of Fe, Zn, Mn-rich marine carbonate sediments. As a minor mineral in some manganese and iron deposits.
It is found associated with Zincite, willemite, calcite, andradite, manganosite, rhodochrosite, gahnite, magnetite, rhodonite, hausmannite, hetaerolite, jacobsite, braunite, sarkinite.
The name refers to Franklin Furnace (now Franklin), New Jersey, USA; and in honor of the American statesman, philosopher, and inventor Benjamin Franklin (1706-1790).
Collections: Collector Favorites, Rare & Remarkable.