Chromite

Chromite

Chromite
 

Composition: Oxide of chromium and iron (FeCr2O4 )

Physical Properties:
Color: Brown
Streak: Black
Luster: Metallic
Hardness: 5.5
Tenacity: Brittle
Specific Gravity: 4.5-4.8
Cleavage: None

Crystallography:
System: Isometric
Twinning:
Habit: Crystals are equant. Aggregates are massive, compact to fine granular.

General Information:
Chromite is a heavy, black mineral that has about the same specific gravity as barite. Its hardness is close to that of steel, but it can usually he scratched with a knife blade. The brown streak (powder of the mineral) ordinarily distinguishes chromite from other similar-appearing heavy black minerals, for most of these have black streaks. Chromite occurs only in peridotite and serpentine, two closely related rock types, or in sand and gravel derived from these rocks. In its host rocks it is normally present as tiny disseminated grains, but in places is concentrated in masses sufficiently large to be mined. Chromite is the only ore mineral of chromium, an important metal that strongly resists corrosion. This metal is an important constituent of stainless steel, and is also used as thin plating to protect the surfaces of other metals that corrode more easily. Chromite is also used in the manufacture of chromium chemicals, that find wide application in leather tanning, pigments, and other industrial uses. In addition, chromite has such a high melting point that it is made into bricks for lining steel-making furnaces. Chromite is a relatively common ore mineral in the Coast Ranges, Sierra Nevada, and Klamath Mountains, and California is the leading producer of the mineral in the United States. Name is from the Greek word chroma, meaning color, for the brilliant hues of its compounds.

California Counties in Which this Mineral is Found
 

Alameda
Amador
Butte
Calaveras
Colusa
Contra Costa
Del Norte
El Dorado
Fresno
Glenn
Humboldt
Kings
Lake
Los Angeles
Madera
Marin
Mariposa
Mendocino
Monterey
Napa
Nevada
Placer
Plumas
Riverside
Sacramento
San Benito
San Bernardino
San Francisco
San Luis Obispo
San Mateo
Santa Barbara
Santa Clara
Santa Cruz
Shasta
Sierra
Siskiyou
Solano
Sonoma
Stanislaus
Tehama
Trinity
Tulare
Tuolumne
Yuba
 

Information on Specimen Photo:
Specimen Description: Chromite, 13.4 cm wide, California Division of Mines and Geology Library.
Photographer: Jeff Scovil