Orpiment

Orpiment
Orpiment

Orpiment
General
Category Sulfide mineral
Chemical formula As2S3
Strunz classification 02.FA.30
Crystal symmetry Monoclinic 2/m
Unit cell a = 11.475(5) Å, b = 9.577(4) Å, c = 4.256(2) Å, β = 90.45(5)°; Z=4
Identification
Color Lemon-yellow to golden or brownish yellow
Crystal habit Commonly in foliated columnar or fibrous aggregates; may be reniform or botryoidal; also granular or powdery; rarely as prismatic crystals
Crystal system Monoclinic Prismatic
Twinning On {100}
Cleavage Perfect on {010}, imperfect on {100};
Tenacity Sectile
Mohs scale hardness 1.5 - 2
Luster Resinous, pearly on cleavage surface
Streak Pale lemon-yellow
Diaphaneity Transparent
Specific gravity 3.49
Optical properties Biaxial (-)
Refractive index nα = 2.400 nβ = 2.810 nγ = 3.020
Birefringence δ = 0.620
Pleochroism In reflected light, strong, white to pale gray with reddish tint; in transmitted light, Y = yellow, Z = greenish yellow
2V angle Measured: 30° to 76°, Calculated: 62°
Dispersion r > v, strong
References [1][2][3]

Orpiment, As2S3, is a common monoclinic arsenic sulfide mineral. It has a Mohs hardness of 1.5 to 2 and a specific gravity of 3.46. It melts at 300 °C to 325 °C. Optically it is biaxial (−) with refractive indices of a=2.4, b=2.81, g=3.02.

orpiment crystals, Humboldt Co., Nevada, USA

Orpiment is an orange to yellow mineral that is found worldwide, and 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. It is often found in association with realgar. It takes its name from the Latin auripigmentum (aurum − gold + pigmentumpigment) because of its deep yellow color.

Contents

Historical uses

Orpiment was an important item of trade in the Roman Empire and was used as a medicine in China although it is highly toxic. It was also used as a fly poison and to poison arrows. Because of its striking color, it was also a favourite with alchemists searching for a way to make gold, both in China and the West.

Orpiment was ground, processed and used for centuries as a pigment in painting and for sealing wax, being one of the few clear, bright yellow pigments available to artists up until the 19th century. Orpiment presented problems, however, such as its extreme toxicity and its incompatibility with other common pigments like lead and copper-based substances such as verdigris and azurite. The use of orpiment as a pigment material ended almost entirely with the advent of the cadmium yellows and the various dye-based colors of the 19th century.

Contemporary uses

It is presently used in the production of infrared-transmitting glass, oil cloth, linoleum; in semiconductors and photoconductors, as a pigment and in fireworks. Mixed with two parts of slaked lime, orpiment is still very commonly used in rural India as a depilatory. It is also used in the tanning industry to remove hair from hides.

Crystal structure

References

  • The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals. 11th Edition. Ed. Susan Budavari. Merck & Co., Inc., N.J., U.S.A. 1989.
  • William Mesny. Mesny’s Chinese Miscellany. A Text Book of Notes on China and the Chinese. Shanghai. Vol. III, (1899), p. 251; Vol. IV, (1905), pp.26.

External links


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Look at other dictionaries:

  • orpiment — [ ɔrpimɑ̃ ] n. m. • XIIe; du lat. auripigmentum, proprt « couleur d or » ♦ Chim. anc. ou techn. Sulfure naturel d arsenic de couleur jaune orangé, utilisé en peinture et dans certaines industries. ● orpiment nom masculin (latin auripigmentum)… …   Encyclopédie Universelle

  • orpiment — ORPIMÉNT s.n. Pigment natural de arsen, de culoare galben strălucitor, folosit ca vopsea în pictură. – Din fr. orpiment. Trimis de ionel bufu, 15.05.2004. Sursa: DEX 98  orpimént s. n. Trimis de siveco, 10.08.2004. Sursa: Dicţionar ortografic … …   Dicționar Român

  • Orpiment — Or pi*ment, n. [F., fr. L. auripigmentum; aurum gold + pigmentum pigment. Cf. {Aureate}, {Pigment}, {Orpin}, {Orpine}.] (Chem.) Arsenic sesquisulphide, produced artificially as an amorphous lemon yellow powder, and occurring naturally as a yellow …   The Collaborative International Dictionary of English

  • orpiment — Orpiment, ou Orpigment, m. acut. Est ce qu on appelle Arsenic rouge, Arsenicum, Auripigmentum …   Thresor de la langue françoyse

  • orpiment — [ôr′pi mənt] n. [OFr < L auripigmentum, pigment of gold: see AURIC & PIGMENT] arsenic trisulfide, As2S3, having a lemon yellow color and a resinous luster: it is used as a pigment …   English World dictionary

  • Orpiment — Cet article concerne le minéral. Pour le pigment, voir orpiment (couleur). Orpiment Catégorie II : sulfures et sulfosels[1] …   Wikipédia en Français

  • Orpiment — Auripigment (engl. Orpiment) Auripigment (gelb) mit einem Restanteil Realgar (rot) Chemische Formel As4S6 Mineralklasse nichtmetallartige Sulfide II/F.02 70 (nach Strunz) 2.11.1.1 (n …   Deutsch Wikipedia

  • orpiment — (or pi man) s. m. Sulfure jaune d arsenic, naturel ou artificiel, employé en peinture, différent du sulfure rouge qui contient moins de soufre et qu on nomme réalgar. •   Les sources [salines] de Montmorot charriaient, disait on, de l arsenic et… …   Dictionnaire de la Langue Française d'Émile Littré

  • orpiment — /awr peuh meuhnt/, n. a mineral, arsenic trisulfide, As2S3, found usually in soft, yellow, foliated masses, used as a pigment. [1350 1400; ME < OF < L auripigmentum pigment of gold; see AURI 1, PIGMENT] * * * ▪ mineralogy  the transparent yellow… …   Universalium

  • orpiment — n. 1 a mineral form of arsenic trisulphide, formerly used as a dye and artist s pigment. Also called yellow arsenic. 2 (in full red orpiment) = REALGAR. Etymology: ME f. OF f. L auripigmentum f. aurum gold + pigmentum pigment …   Useful english dictionary

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