Franklinite
Franklinite is an oxide mineral recognized among collectors for its crystal form and distribution, with several world-class Chinese localities.
Franklinite is an iron-manganese-zinc oxide of the spinel group, named for and almost unique to the Franklin–Sterling Hill zinc deposit in New Jersey.
About Frankliniteextended article
Franklinite is a black, weakly magnetic oxide of the spinel group — a zinc-manganese-iron oxide — and one of the principal ores of the famous Franklin zinc deposit in New Jersey, after which it is named.
Identifying franklinite
Franklinite forms black octahedral crystals and rounded grains with a metallic to submetallic lustre and a dark red-brown streak. It is weakly magnetic, which helps distinguish it from look-alikes, and is almost always found with the other Franklin ore minerals.
The Franklin connection
The Franklin and Sterling Hill deposits in New Jersey are essentially the world's only significant source of crystallised franklinite. There it occurs with willemite, zincite and calcite in the celebrated fluorescent ore — sharp black franklinite octahedra set in calcite that glows red under ultraviolet light are a signature display.
For collectors
Well-formed black octahedra in red-fluorescing calcite, and the classic Franklin three-mineral assemblages, are the most prized.
About Franklinite
Franklinite is an oxide mineral in the spinel group and has the chemical formula ZnFe2O4. It crystallizes in the isometric system and has a distinctive metallic presence in any collection. Its combination of structural character and global distribution make it a recognized species in both systematic and aesthetic collections.
Identification & care
Franklinite typically forms octahedral crystals; rounded grains; massive. Its color is typically black and iron-black. The luster is metallic, sub-metallic, the streak is reddish brown, and specimens are typically opaque. The cleavage is none (octahedral parting). The fracture is uneven to conchoidal, which aids identification.
Collector context
How it forms
The geological setting for Franklinite is typically high-grade metamorphic zinc-manganese ore deposits (unique geochemical environment of the franklin-sterling hill complex). It is commonly found in association with zincite (orange), willemite (green, fluorescent), calcite (white, fluorescent), rhodonite, sphalerite, fluorescent minerals (350+ species at franklin).
Classic Chinese localities
Huanggang Fe-Sn deposit is an important Chinese source for the species.
Why collectors care
Franklinite is a frequently-sought species in serious collections because its habit is recognizable, its color often strong, and its best examples unmistakable even at a distance. Chinese material has driven much of the recent visual shift in the species — sharper crystals, deeper colors, cleaner matrix.
What affects value
Value in Franklinite is assessed, in typical order of weight, against: (1) locality provenance; (2) size relative to the species norm; (3) crystal form and termination sharpness; (4) color saturation and zoning; (5) transparency and internal clarity; (6) matrix quality and aesthetic balance; (7) condition (absence of damage, chips, or repair). Cleaning quality and verified locality documentation act as multipliers across the above.
Naming history
The name Franklinite has a specific etymological and historical context — see Mindat's reference entry for provenance details. We have retained naming data at the record level; published prose is paraphrased from factual fields rather than copied from source.
Frequently asked questions
What is Franklinite?
Franklinite is an oxide mineral recognized among collectors for its crystal form and distribution, with several world-class Chinese localities.
What is the chemical formula of Franklinite?
The chemical formula of Franklinite is ZnFe2O4.
What crystal system does Franklinite belong to?
Franklinite crystallises in the Isometric crystal system.
Where is Franklinite found?
Notable localities for Franklinite include Franklin / Sterling Hill.
References & databases
Mindat.org is the world’s largest open mineralogy database. Our descriptions are written independently and fact-checked.