Pyrite

Pyrite

Pyrite
 

Composition: Iron sulfide (FeS2)

Synonyms/Varieties:
Fool's Gold

Physical Properties:
Color: Pale brass yellow
Streak: Greenish black or brownish black
Luster: Metallic
Hardness: 6-6.5
Tenacity: Brittle
Specific Gravity: 5.02
Cleavage: None

Crystallography:
System: Isometric
Twinning: Common
Habit: Crystals are cubic, pyritohedral, and octahedral. Aggregates are massive, disseminated, granular, reniform, botryoidal and stalactitic.

General Information:
Pyrite is a heavy, metallic-appearing mineral that is often mistaken for gold because of its color, and is, in fact, often referred to as fools gold. However, it is not really metallic, but brittle, and has a greenish-black streak (gold is malleable, and has a gold-colored streak). Where it is disseminated in rocks, pyrite commonly exhibits its most frequent crystal form, the cube. These cubic crystals are so diagnostic of pyrite that when they are present, the mineral can be recognized even though the crystal surfaces are altered to brown limonite, which is often the case. But much pyrite is fine-grained or massive, and does not have crystal faces. The fact that pyrite cannot be scratched with a knife blade is usually sufficient to distinguish it from other similar-colored sulfide minerals, for with one exception they are all softer than steel. The only other sulfide mineral equally hard is a relatively rare one, marcasite, that has the same chemical formula as pyrite, but a different lattice structure. Pyrite is a relatively abundant and widespread mineral, occurring in places in all types of rocks. It is perhaps best known for its occurrences in quartz veins, where it is commonly associated with gold and other metallic ore minerals. Thus, when pyrite is found in a quartz vein, it is in indication to the geologist and prospector that valuable metals may be present in the vein. Pyrite itself is of value as an ore of sulfur, and a large deposit of it in Shasta County is mined for this purpose.

California Counties in Which this Mineral is Found
 

Alameda
Alpine
Amador
Calaveras
Colusa
El Dorado
Fresno
Imperial
Inyo
Kern
Lake
Madera
Mariposa
Mendocino
Mono
Nevada
Riverside
San Bernardino
San Diego
Santa Clara
Santa Cruz
Shasta
Siskiyou
Sonoma
Trinity
Tuolumne
 
 

Information on Specimen Photo:
Specimen Description: Pyrite, 10.7 cm wide, Inyo County. California State Mining and Mineral Museum.
Photographer: Jeff Scovil