Magnetite

Magnetite

Magnesite
 

Composition: Iron oxide (Fe3O4)

Synonyms/Varieties:
Lodestone

Physical Properties:
Color: Brownish to black
Streak: Black
Luster: Metallic to semi-metallic, splendant to dull
Hardness: 5.5-6.5
Tenacity: Brittle
Specific Gravity: 5.18
Cleavage: None

Crystallography:
System: Isometric
Twinning: Common
Habit: Crystals are octahedral and dodecahedral. Aggregates are massive, compact, and fine to coarse granular.

General Information:
Magnetite is a heavy black mineral that is easily identified because it is strongly attracted by a magnet. A few other minerals are weakly attracted by magnets, but they either do not look like magnetite or their streaks are not black. Magnetite from some localities acts as a natural magnet (that is, will attract iron filings), and is called lodestone. Magnetite is a relatively abundant mineral, for it is a minor constituent of many different types of rocks. Where it is sparser disseminated as large grains in some rocks, the characteristic octahedral crystal form of magnetite is often identifiable. However, the grains are most commonly irregular in shape. Being an oxide, magnetite is highly resistant to alteration by weathering, so grains of it tend to accumulate in sands. As a result, the easiest way to find magnetite is to thrust a magnet into the sand of almost any stream or beach. Magnetite is a very important mineral to our industrial economy, for it is one of the principal ore minerals of iron.

California Counties in Which this Mineral is Found
 

Butte
Calaveras
Del Norte
El Dorado
Fresno
Inyo
Kern
Los Angeles
Madera
Mono
Nevada
Placer
Plumas
Riverside
San Benito
San Bernardino
Santa Cruz
Shasta
Sierra
Trinity
 

Information on Specimen Photo:
Specimen Description: Magnetite, right crystal 2.3 cm high, San Gabriel Mountains, Los Angeles County. California State Mining and Mineral Museum.
Photographer: Jeff Scovil