New Jersey State Mineral
Magnetite is an iron oxide mineral and an important ore of iron. While its principal components are iron and oxygen, it may contain traces of many other elements. The mineral is black but can form a yellow-brown rust if exposed to moisture. A very common mineral in general, magnetite is the most common mineral occurring in black sands. Because magnetite is also very heavy, when the wind blows, the lighter-weight sand is blown away, leaving magnetite patches behind.
As its name indicates, magnetite has a strong attraction to magnets and is the most magnetic naturally occurring mineral. A somewhat less common variety of magnetite called lodestone is the only mineral that actually acts as a magnet. Lodestone has definite north and south poles and was used in early magnetic compasses. Magnetite is a member of the spinel group and forms two series: one with jacobsite, and one with magnesioferrite.
For a time during the 19th century, New Jersey was the nation’s principal supplier of magnetite for production of iron. At that time, vast stores of magnetite in the gneiss deposits in the northern part of the state were mined. Since New Jersey has no coal or petroleum deposits, smelting the iron ore locally was not economical. The ore was transported by mule-drawn barge.
When iron ore was found in Michigan, with easy access to the Great Lakes, New Jersey mines could not compete and were abandoned. Approximately 500 abandoned iron mines now dot northwest and north central New Jersey. The Garden State does not have an official state mineral. A symbol of New Jersey’s mining past, magnetite also represents the state’s history, economy, and geology.
Magnetite was named for its strong magnetism. "Magnetism" is an ancient term, possibly coming from Magnesia, Greece, a locality for lodestone.
FORMATION AND OCCURRENCE
Most commonly, magnetite is an accessory mineral in igneous rocks. It also occurs as beds or lenses in metamorphic rocks. In fact, trace amounts of magnetite occur in almost all metamorphic and igneous rocks. Magnetite also occurs in sedimentary-banded iron formations. Sometimes found in beach sand in large quantities, magnetite is frequently associated with the heavy fraction of beach and river sands because of its resistance to weathering. This mineral occurs in well-formed crystals and rounded grains. Magnetite forms in association with talc, pyrite, hematite, apatite, chlorite, and quartz.
Since magnetite is a very common mineral, only a few localities for fine specimens are mentioned here.
Magnetite is one of the principal ore minerals of iron. An estimated 98 percent of the ore shipped in the world is consumed by the iron and steel manufacturing industry. The Lake Superior district still produces the bulk of the iron ore in the U.S., and almost all of the ore being recovered is magnetite.
Magnetite is also important to geologists and mineralogists because of its magnetic properties. Because magnetite may record past directions of the earth’s magnetic field, the mineral makes the study of paleomagnetism possible.
This mineral’s well-formed crystals are popular with mineral collectors. When polished, magnetite makes dark, shiny jewelry. It is a popular element in the theory of magnetic therapy. Those who practice this controversial alternative therapy believe that static magnetic fields can have beneficial effects on the blood and overall health.
Chemical Formula: Fe2+Fe3+2O4
Crystal Structure: Typically octahedral, less commonly
Hardness (Mohs): 5½-6½
Color: Greyish black or iron black
Luster: Metallic, sub-metallic
Density: 5.175 g/cm3
Cleavage: Imperfect on the 
Some data courtesy of the Mineralogical Society of America
Author: World Trade Press