Stubby metallic crystals of Franklinite in Calcite from Franklin, New
Jersey.
A single,
large (3 inches across) crystal of Octahedral Franklinite. The matrix
consists of light colored calcite and reddish brown zincite. This specimen
is from Franklin, New Jersey. This specimen is part of the Arizona Mining
and Mineral Museum. Catalog # MM-T090.
CHEMISTRY (Zn,Fe2+,Mn2+)(Fe3+Mn3+)2O4
Basically a zinc-iron oxide but always with a substitution of Mn for Fe.
CRYSTALLOGRAPHY Isometric (Cubic)
CRYSTAL GROWTH AND HABITS Franklinite is common as octahedrons, occasionally with dodecahedral truncations. Franklinite can also be massive and coarse to fine grained.
COLOR AND OTHER OPTICAL PROPERTIES Its color is iron black to reddish black, opaque to translucent in thin pieces.
HARDNESS 6
SPECIFIC GRAVITY 5.0 - 5.2
LUSTER Metallic to dull
STREAK Reddish brown to black
BREAKABILITY Franklinite has an uneven fracture, is brittle with a fair breakage along parting planes.
OCCURRENCE Franklinite is found as beds or in veins produced by the metamorphism of iron, zinc, manganese rich marine carbonates.
ASSOCIATED MINERALS Willemite, Zincite, Calcite
OTHER PROPERTIES Franklinite may be slightly magnetic.