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Orpiment

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Formula:
As2S3
System:
Monoclinic
Colour:
Orange-yellow to ...
Lustre:
Pearly
Hardness:
1½ - 2
Name:
From Latin "aurum", gold, and "pigmentum", pigment, in allusion to its color.
May be visually similar to uzonite.

Classification of Orpiment

Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
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, H2O
A : With As, (Sb), S
2.11.1.1

2 : SULFIDES
11 : AmBnXp, with (m+n):p = 2:3
3.7.8

3 : Sulphides, Selenides, Tellurides, Arsenides and Bismuthides (except the arsenides, antimonides and bismuthides of Cu, Ag and Au, which are included in Section 1)
7 : Sulphides etc. of V, As, Sb and Bi
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Occurrences of Orpiment

Geological Setting:
In low-temperature hydrothermal veins, hot springs and fumaroles; also commonly as an alteration product of arsenic minerals, especially realgar.

Physical Properties of Orpiment

Pearly
Diaphaneity (Transparency):
Transparent
Colour:
Orange-yellow to lemon-yellow
Streak:
Light lemon yellow
Hardness (Mohs):
1½ - 2
Tenacity:
Sectile
Cleavage:
Perfect
Perfect {010} imperfect {100}
Density:
3.49 g/cm3 (Measured)    3.48 g/cm3 (Calculated)

Crystallography of Orpiment

Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Cell Parameters:
a = 11.475(5) Å, b = 9.577(4) Å, c = 4.256(2) Å
β = 90.45(5)°
Ratio:
a:b:c = 1.198 : 1 : 0.444
Unit Cell Volume:
V 467.70 ų (Calculated from Unit Cell)
Z:
4
Morphology:
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.
Twinning:
On {100}
Comment:
sp. gr. P21/n

Crystallographic forms of Orpiment

Crystal Atlas:
Image Loading
Click on an icon to view
Orpiment no.3 - Goldschmidt (1913-1926)
Orpiment no.13 - Goldschmidt (1913-1926)
Orpiment - Tabular {010}
3d models and HTML5 code kindly provided by www.smorf.nl.

Toggle
Edge Lines | Miller Indicies | Axes

Transparency
Opaque | Translucent | Transparent

View
Along a-axis | Along b-axis | Along c-axis | Start rotation | Stop rotation
X-Ray Powder Diffraction:
Image Loading

Radiation - Copper Kα
Data Set:
Data courtesy of RRUFF project at University of Arizona, used with permission.
X-Ray Powder Diffraction Data:
d-spacingIntensity
4.85 (100)
4.02 (50)
3.22 (30)
2.79 (30)
2.72 (30)
2.47 (40)
1.755 (40)
Comments:
Baia Sprie (Felsőbánya), Romania.

Optical Data of Orpiment

Type:
Biaxial (-)
RI values:
nα = 2.400 nβ = 2.810 nγ = 3.020
2V:
Measured: 30° to 76°, Calculated: 62°
Max Birefringence:
δ = 0.620
Image shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:
Very High
Type:
Anisotropic
Anisotropism:
Barely observable because of strong internal reflections
Dispersion:
relatively strong r > v
Reflectivity:
400nmR1=33.0%R2= 36.5%
420nmR1=31.0%R2= 35.2%
440nmR1=28.9%R2= 33.9%
460nmR1=27.4%R2= 31.5%
480nmR1=26.0%R2= 30.3%
500nmR1=24.9%R2= 29.3%
520nmR1=24.0%R2= 28.4%
540nmR1=23.3%R2= 27.8%
560nmR1=22.8%R2= 27.3%
580nmR1=22.3%R2= 26.9%
600nmR1=22.0%R2= 26.5%
620nmR1=21.7%R2= 26.3%
640nmR1=21.5%R2= 26.0%
660nmR1=21.2%R2= 25.7%
680nmR1=21.0%R2= 25.5%
700nmR1=20.8%R2= 25.3%

Reflectance graph
Graph shows reflectance levels at different wavelengths (in nm). Top of box is 100%. Peak reflectance is 36.5%.
R1 shown in black, R2 shown in red
Colour in reflected light:
White to pale grey
Internal Reflections:
Strong
Pleochroism:
Strong
Comments:
white to grey white with reddish tint (reflected light)
Y=yellow, Z=greenish yellow (transmitted light)

Chemical Properties of Orpiment

Formula:
As2S3
Essential elements:
All elements listed in formula:
Common Impurities:
Hg,Ge,Sb

Relationship of Orpiment to other Species

2.FA.05DuranusiteAs4S
2.FA.10DimorphiteAs4S3
2.FA.15bPararealgarAs4S4
2.FA.15aRealgarAs4S4
2.FA.15cUM1970-19-S:AsAs4S4
2.FA.15dUM1970-18-S:AsAs4S4
2.FA.20AlacrániteAs8S9
2.FA.25UzoniteAs4S5
2.FA.30LaphamiteAs2(Se,S)3
2.FA.35GetchelliteAsSbS3
2.FA.40Wakabayashilite[(As,Sb)6S9][As4S5]
3.7.1PatróniteVS4
3.7.2DuranusiteAs4S
3.7.3DimorphiteAs4S3
3.7.4RealgarAs4S4
3.7.5PararealgarAs4S4
3.7.6AlacrániteAs8S9
3.7.7UzoniteAs4S5
3.7.9Jeromite
3.7.10LaphamiteAs2(Se,S)3
3.7.11GetchelliteAsSbS3
3.7.12Wakabayashilite[(As,Sb)6S9][As4S5]
3.7.13PääkköneniteSb2AsS2
3.7.14StibniteSb2S3
3.7.15MetastibniteSb2S3
3.7.16TellurantimonySb2Te3
3.7.17BismuthiniteBi2S3
3.7.18NevskiteBi(Se,S)
3.7.19GuanajuatiteBi2Se3
3.7.21IkunoliteBi4(S,Se)3
3.7.22LaitakariteBi4Se2S
3.7.23PoubaitePbBi2(Se,Te,S)4
3.7.24TellurobismuthiteBi2Te3
3.7.25SoučekitePbCuBi(S,Se)3
3.7.26TsumoiteBiTe
3.7.27PilseniteBi4Te3
3.7.28HedleyiteBi7Te3
3.7.29TetradymiteBi2Te2S
3.7.30JoséiteBi4TeS2
3.7.31Joséite-BBi4Te2S
3.7.32IngoditeBi2TeS
3.7.33SulphotsumoiteBi3Te2S
3.7.34KawazuliteBi2Te2Se
3.7.36SkippeniteBi2TeSe2
3.7.37KochkaritePbBi4Te7
3.7.38Rucklidgeite(Bi,Pb)3Te4
3.7.39AleksitePbBi2Te2S2
3.7.40JunoiteCu2Pb3Bi8(S,Se)16

Other Names for Orpiment

Other Information

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Orpiment

Reference List:
Palache, Charles, Harry Berman & Clifford Frondel (1944), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892, Volume I: Elements, Sulfides, Sulfosalts, Oxides. John Wiley and Sons, Inc., New York. 7th edition, revised and enlarged: 266-269.

Mullen, D.J.E. and Nowacki, W. (1972): Refinement of the crystal structures of realgar, AsS and orpiment, As2S3. Zeitschrift für Kristallographie, 136, 48-65.

Bonazzi, P. & Bindi, L. (2008): A crystallographic review of arsenic sulfides: Effects of chemical variations and changes induced by exposure to light. Zeitschrift für Kristallographie, 223, 132-147.

Internet Links for Orpiment

Specimens:
The following Orpiment specimens are currently listed for sale on minfind.com.

Localities for Orpiment

map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
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