Franklinite

Franklinite is named is named after its discovery locality, at Franklin and Sterling Hill, Sussex County, New Jersey, and ultimately for Benjamin Franklin, after whom the town of Franklin was named.

Franklinite forms iron-black, brown, red crystals with metallic lustre. Large crystals suitable for faceting are rare.

General Information
Chemical Formula
(Zn,Mn
2+
 
,Fe
2+
 
)(Fe
3+
 
,Mn
3+
 
)
 
2
O
 
4
Anthony et al, Handbook of mineralogy (2001)
Photos of natural/un-cut material from mindat.org
Physical Properties of Franklinite
Mohs Hardness6 to 0
Anthony et al, Handbook of mineralogy (2001)
Specific Gravity5.05 to 5.22
Anthony et al, Handbook of mineralogy (2001)
TenacityBrittle
Anthony et al, Handbook of mineralogy (2001)
Cleavage QualityFair
Anthony et al, Handbook of mineralogy (2001)
FractureUneven,Sub-Conchoidal
Anthony et al, Handbook of mineralogy (2001)
Optical Properties of Franklinite
Optical CharacterIsotropic
Anthony et al, Handbook of mineralogy (2001)
Colour
Colour (General)Iron-black, brown, red, may be tarnished; in reflected light, white to gray, with dark red internal reflections
Anthony et al, Handbook of mineralogy (2001)
TransparencyTranslucent,Opaque
Anthony et al, Handbook of mineralogy (2001) Translucent in fine fragments
LustreDull (Earthy),Metallic,Submetallic
Anthony et al, Handbook of mineralogy (2001)
Crystallography of Franklinite
Crystal SystemIsometric
Anthony et al, Handbook of mineralogy (2001)
HabitTypically as octahedra, commonly with rounded edges, to 22 cm. Also exsolved within other minerals; coarse to fine granular, massive.
Anthony et al, Handbook of mineralogy (2001)
Geological Environment
Where 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.
Anthony et al, Handbook of mineralogy (2001)
Further Information
Mineral information:Franklinite information at mindat.org
Significant Gem Localities
USA
 
  • New Jersey
    • Sussex Co.
      • Franklin Mining District
        • Franklin
Copyright © Jolyon & Katya Ralph 1993-2019. Site Map. Locality, gem & photograph data are the copyright of the individuals who submitted them. For more information please contact the . Gemdat.org is an online information resource dedicated to providing free gemmological information to all.