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Orpiment
Current inventory:  1 gem
 

   

Orpiment

Chemistry:  As2S3

Discovered in 1747;   IMA status: Valid (pre-IMA; Grandfathered).
Orpiment is named from the Latin words aurum meaning gold and pigmentum meaning pigment, in allusion to the vivid golden color.

 

Classification

   

   

Mineral Classification:

Sulfides

Strunz 8th Ed. ID:

2/F.02-70

Nickel-Strunz 10th Ed. ID:

2.FA.30

 

2 : SULFIDES and SULFOSALTS (sulfides, selenides, tellurides; arsenides, antimonides, bismuthides; sulfarsenites, sulfantimonites, sulfbismuthites, etc.)
F : Sulfides of arsenic, alkalies; sulfides with halide, oxide, hydroxide, H
2O
A : With As, (Sb), S

Related to:

Duranusite - Jeromite Series

 

 

Crystal Data

   

   

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Commonly in foliated columnar or fibrous aggregates, with cleavages as much as 60 cm across; may be reniform or botryoidal; also granular or powdery; rarely as prismatic crystals, to 10 cm. Twinning: On [100].

Twinning:

On [100]

 

 

Physical Properties

   

 

Cleavage:

[010] Perfect, [100] Imperfect; cleavage lamellae are flexible

Fracture:

Sectile (curved shavings)

Tenacity:

Brittle

Moh's Hardness:

1.5 - 2.0

Density:

3.49 - 3.56 (g/cm3)

Luminescence:

None

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:

Lemon Yellow, Brownish Yellow, Orange Yellow

Transparency:

Transparent to Translucent

Luster:

Pearly Barely observable because of strong internal reflections.

Refractive Index:

2.40 - 3.02  Biaxial ( - )

Birefringence:

0.620

Dispersion:

Very Strong (r > v)

Pleochroism:

Strong: white to gray white with reddish tint (reflected light)
Y=yellow, Z=greenish yellow (transmitted light)

Anisotropism:

Barely observable because of strong internal reflections.

 

 

Occurances

   

   

Geological Setting:

Occurs as a sublimation product in volcanic fumaroles, low temperature hydrothermal veins, hot springs and as a byproduct of the decay of another arsenic mineral, Realgar.

Common Associations:

Arsenic, Barite, Calcite, Gypsum, Realgar, Stibnite

Type Locality:

n/a

Year Discovered:

1747

View mineral photos:

Orpiment Mineral Photos and Locations

 

 

More Information

   

   

 

Mindat.org
Webmineral.com

 

 


Orpiment is a mineral that is not uncommon in small amounts, but rare as fine specimens or large crystals. Orpiment is a very interesting mineral in that it has very high RI values, very high birefringence, very stong internal reflections, very strong dispersion, very high density, very strong pleochroism and is also anisotropic. Orpiment is also dangerous since it contains about 61% Arsenic. Arsenic and its compounds are poisonous. Because of this, and the fact that Orpiment has perfect cleavage, sectile fracture and very low Moh's hardness, it is not available as a faceted gemstone but may very rarely be found as a cabochon. Although handling is dangerous, Orpiments vivid colors do make for beautiful mineral specimens and a very rare cabochon for collectors.

Orpiment occurs in many locations worldwide but only a few produce fine specimens or large crystals. Crystals can be found at Mercur, Tooele County, Utah, USA; at the Getchell and Twin Creeks mines, Humboldt County, and the White Caps mine, Manhattan, Nye County, Nevada, USA; fine crystals from the Zarshuran gold deposit, north of Takab, northwestern Iran; large crystals from the Shimen mine, Hunan Province, China; and exceptional specimens from the Quiruvilca mine, La Libertad, Peru.
 

  
Orpiment gems for sale:

Orpiment-001

Gem:

Orpiment

Stock #:

ORP-001

Weight:

14.3435 ct

Size:

29.66 x 15.12 x 4.81 mm

Shape:

Free-form triangle

Color:

Orangish Yellow

Clarity:

Opaque

Origin:

Barney's Canyon, Utah, USA

Treatment:

None (natural)

Price:

$89.00

Pictures are of the actual gem offered for sale.
Gem images are magnified to show detail.

Orpiment-001

A very rare gem with beautiful, intense color. This gem is from the Melco deposit, Barney's Canyon, Bingham District (West Mountain District), Oquirrh Mountains, Salt Lake County, Utah, USA.




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