Mineral - Marcasite
Marcasite
Chemical Properties
Mineral Class
Sulfides and sulfosalts
Toxicity
none
Formula
FeS₂
Unit Cell
a=4.44 b=5.41 c=3.38 Z=2
Physical Properties
Hardness
6 - 6.5
Streak
graygreengreen grey
Density
Heavy (3,5-6)
Cleavage
Distinct after {101}
Fracture
conchoidal
Tenacity
Brittle
Optical Properties
Color
yellowbronze
Birefringence
Luster
Metallic
Transparency
opaque
Pleochroism
Geomineralogical Properties
Crystal System
orthorhombic
Point Group
orthorhombic-dipyramidal - 2/m 2/m 2/m
Space Group
Pnnm (58)
Habit
prismatic, pyramidal, radial, tabular
Formation
(1) Primarily through precipitation from hydrothermal solutions at low temperatures (< 240 °C) and acidic pH values (pH < 5) under reducing conditions.
(2) Syngenetic as a diagenetic formation in reducing, organic-rich sediments (e.g., coal, clays) from sulfide-containing pore waters.
(3) Secondary as a conversion product of other iron sulfides (especially magnetite) under near-surface, mostly acidic conditions.
Paragenesis
Twinning
Spearhead-shaped contact twins after {101}, that often build on each other (Speerkies); Coffin-shaped rotational twins (fourlings) after {101}
Rarity
Common
Synonyms
Marcasite
Composition
Elements
Mass
Fe
46.53
S
53.30
Missouri (Palache et al. 1952)
Groups and Members
Marcasite-Group