Arsenopyrite
Current inventory:  0 gems
 

  
Arsenopyrite was named for its composition, a contraction of the antiquated term "arsenical pyrite."

Discovered in 1847;  IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

FeAsS

Iron Arsenide Sulfide

Molecular Weight:

162.83 gm

Composition:

Iron

34.30 %

Fe

Arsenic

46.01 %

As

Sulfur

19.69 %

S

100.00 %

Classification

Mineral Classification:

Sulfides

Strunz 8th Ed. ID:

2/D.22-10

Nickel-Strunz 10th Ed. ID:

2.EB.20

2 : SULFIDES and SULFOSALTS (sulfides, selenides, tellurides; arsenides, antimonides, bismuthides; sulfarsenites, sulfantimonites, sulfbismuthites, etc.)
E : Metal Sulfides, M: S <= 1:2
B : M:S = 1:2, with Fe, Co, Ni, PGE, etc.

Related to:

Arsenopyrite Group. Arsenopyrite is closely related to Alloclasite, but is not an exact analogue, because of different As-S and S-As ordering.

Members of Group:

Arsenopyrite Group: Arsenopyrite, Gudmundite, Osarsite, Ruarsite

Varieties:

Danaite

Synonyms:

Arsenical Iron, Arsenical Pyrites, Arsenomarcasite, Dalarnite, Plinian, Thalheimite  

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Crystals, to 30 cm, flat tabular to blocky to prismatic, striated k [001]. Also compact, granular, columnar.

Twinning:

Common on {100} and {001}; as contact or penetration twins on {101}; on {012} to produce star-shaped trillings or cruciform twins.

Physical Properties

Cleavage:

Distinct on {101}; {010} in traces. 

Fracture:

Irregular/Uneven

Tenacity:

Brittle

Moh's Hardness:

5.5 – 6.0

Vicker's Hardness:

VHN₁₀₀=1081 kg/mm²

Density:

6.07 (g/cm³)

Luminescence:

Not Fluorescent

Radioactivity:

Not Radioactive

Health Warning:

CAUTION: Contains Arsenic, a poisonous element - always wash hands after handling. Avoid inhaling dust when handling or breaking. Never lick or ingest.

Optical Properties

Color:

Silver-white to steel-gray; in polished section, white with faint yellow tint.

Transparency:

Opaque

Luster:

Metallic

Refractive Index:

R1–R2: (400) 50.3–51.8, (420) 50.3–51.8, (440) 51.3–51.8, (460) 50.6–51.8, (480) 51.0–51.9, (500) 51.4–51.9, (520) 51.8–51.9, (540) 52.2–51.9, (560) 52.5–51.9, (580) 53.0–51.8, (600) 53.4–51.6, (620) 53.6–51.5, (640) 53.6–51.3, (660) 53.6–51.3, (680) 53.4–51.2, (700) 53.2–51.0

Birefringence:

0.00 (opaque)

Dispersion:

n/a

Pleochroism:

Weak; in white or bluish tint and faint reddish yellow.

Anisotropism:

Strong; Color in reflected light: red-violet

Occurances

Geological Setting:

Of hydrothermal origin, typically one of the earliest minerals to form. Found in pegmatites, high-temperature gold-quartz and tin veins, and in contact metamorphic sulfide deposits; less commonly of low-temperature hydrothermal origin. Also in gneisses, schists and other metamorphic rocks.

Common Associations:

Pyrrhotite, Pyrite, Chalcopyrite, Galena, Gold, Scheelite, Cassiterite, many other species.

Common Impurities:

Ag, Au, Co, Sn, Ni, Sb, Bi, Cu, Pb

Type Locality:

n/a

Year Discovered:

1847

View mineral photos:

Arsenopyrite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Arsenopyrite is the most common arsenic bearing mineral found world wide. However, it is not intentionally mined for that reason. Arsenopyrite may contain a small amount of gold as an impurity. Arsenopyrite makes attractive mineral specimens but is rarely available as a faceted gem. Arsenopyrite is found in colors of silver-white to steel-gray and may have a sulfur smell when struck.

Distribution: The most abundant and widespread arsenic mineral; only a few localities for large and fine crystals can be mentioned. In Germany, from Altenberg, Ehrenfriedersdorf, and Freiberg, Saxony. In the Stari Trg mine, Trepca, Serbia. From Panasqueira, Portugal. At Sala, Tunaberg, Stollberg, Boliden, and Nordmark, Sweden. From Stratonik, Greece. In England, from a number of mines in Cornwall, and in Devonshire, at Tavistock. In the USA, from Franconia, Grafton County, New Hampshire and Franklin, Sussex County, New Jersey. From Hidalgo del Parral and Santa Eulalia, Chihuahua, Mexico. In Canada, in the Cobalt district, Ontario. In Japan, large crystals in the Obira mine, Bungo, Oita Prefecture; the Ashio mine, Tochigi Prefecture; and many other localities.
 

  
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