Crystal Marcasite

Chemical Formula

FeS₂

Composition

Iron sulfide

Color

Pale brass-yellow to nearly white. Tarnishes to a dark brass-like brown or with iridescent colors.

Streak

Dark brown to black, with slightly green tinge

Hardness

6 - 6.5

Crystal System

Orthorhombic

Crystal Forms 
and Aggregates

Usually as bipyramidal and tabular crystals, commonly in coxcomb aggregates and bladed. Crystals frequently form curved formations as well as herringbone patterns. Also occurs massive, radiating, mammilary, encrusting, nodular, as groups of small crystals, and in radiating discs known as dollars. Commonly forms as pseudomorphs over other minerals and fossils, resulting in bizarre shapes and forms. 
 

Transparency

Opaque

Specific Gravity

4.8 - 4.9

Luster

Metallic

Cleavage

2,2 - Prismatic

Fracture

Conchoidal

Tenacity

Brittle

Other ID Marks

Tarnishes to a dark brass-like brown.
 

In Group

Sulfides; Simple Sulfides

Striking Features

High hardness, color, heaviness, and streak

Environment

Mainly in sedimentary deposits and low temperature ore veins, also in skarn metamorphic deposits.
 

Rock Type

Sedimentary, Metamorphic

Popularity (1-4)

2

Prevalence (1-3)

2

Demand (1-3)

2