Arsenic is a native element with the formula As and atomic number 33. Known since antiquity, arsenic is widely distributed in nature, although it is unusual in native form. It is classified as a semimetal, because it possesses some properties of metals and some of nonmetals. Crystals are rare, but when found they are rhombohedral. It usually occurs in massive, botryoidal to reniform, or stalactitic habits, often with concentric layers. On fresh surfaces, arsenic is tin-white, but it quickly tarnishes to dark gray. Native arsenic is found in hydrothermal veins, often associated with antimony, silver, cobalt, and nickel-bearing minerals. It is highly poisonous, although it is used in some medicines to treat infections. Arsenic-based compounds can be used in alloys to increase high-temperature strength and as a herbicide and pesticide.

The United States’ Environmental Protection Agency states that all forms of arsenic are a serious risk to human health. The United States’ Agency for Toxic Substances and Disease Registry ranked arsenic as number 1 in its 2001 Priority List of Hazardous Substances at Superfund sites. Arsenic is classified as a Group-A carcinogen. (Wikipedia, 2019)

Name: From the Latin arsenicum, earlier Greek arrenikos, or arsenikos, masculine, an allusion to its potent properties.

Association: Arsenolite, cinnabar, realgar, orpiment, stibnite, galena, sphalerite, pyrite, barite

Polymorphism & Series: Dimorphous with arsenolamprite.

Mineral Group: Arsenic group.

Cell Data: Space Group: R3m (synthetic). a = 3.7598(1) c = 10.5475(2) Z = 6

Morphology: Granular, massive, concentric layered. Reticulated, reniform, stalagtitic, columnar, acicular. small rhombohedra.

Chemical Properties

Chemical Classification Native Element
Formula As
Common Impurities Bi,Sb,Fe,Ni,Ag,S,Se

Arsenic Physical Properties

Color Tin-white, tarnishing to dark grey or black.
Streak Grey
Luster Metallic, Dull
Cleavage Perfect Perfect basal on {0001}, fair on {0114}
Diaphaneity Opaque
Mohs Hardness 3,5
Crystal System Trigonal
Tenacity Brittle
Density 5.63 – 5.78 g/cm3 (Measured)    5.778 g/cm3 (Calculated)
Fracture Irregular/Uneven

Arsenic Optical Properties

Type Anisotropic
Anisotropism Distinct – yellowish brown and light grey to yellowish grey
Color / Pleochroism Weak
Twinning Rare on {1014}, Pressure twinning on {0112}

Occurrence

In hydrothermal veins and deposits that contain other arsenic minerals; may be in Co–Ag sulfide veins.

Arsenic comprises about 1.5 ppm (0.00015%) of the Earth’s crust, and is the 53rd most abundant element. Typical background concentrations do not exceed 3 ng/m3 in the atmosphere; 100 mg/kg in soil; and 10 μg/L in freshwater.

Arsenic Uses Area

  • The toxicity of arsenic to insects, bacteria, and fungi led to its use as a wood preservative
  • It was also used in various agricultural insecticides and poisons. For example, lead hydrogen arsenate was a common insecticide on fruit trees.
  • It is used as a feed additive in poultry and swine production, in particular in the U.S. to increase weight gain, improve feed efficiency, and to prevent disease
  • It is intentionally added to the feed of chickens raised for human consumption. Organic compounds are less toxic than pure arsenic, and promote the growth of chickens. Under some conditions, the arsenic in chicken feed is converted to the toxic inorganic form.
  • Medical use
  • During the 18th, 19th, and 20th centuries, a number of arsenic compounds were used as medicines, including arsphenamine (by Paul Ehrlich) and arsenic trioxide (by Thomas Fowler).
  • Arsenic trioxide has been used in a variety of ways over the past 500 years, most commonly in the treatment of cancer, but in medications as diverse as Fowler’s solution in psoriasis.
  • The main use is in alloying with lead. Lead components in car batteries are strengthened by the presence of a very small percentage of arsenic.
  • Gallium arsenide is an important semiconductor material, used in integrated circuits. Circuits made from GaAs are much faster (but also much more expensive) than those made from silicon.

Distribution

Numerous localities are known, most of only minor interest.

  • In Germany, from Freiberg, Schneeberg, Johanngeorgenstadt, Marienberg, and Annaberg, Saxony; Wolfsberg and St. Andreasberg, Harz Mountains; and Wieden, Black Forest.
  • In the Gabe-Gottes mine, Rauenthal, near Sainte-Marie-aux-Mines, Haut-Rhin, France. At Jachymov (Joachimsthal), Prıbram, and Cınovec (Zinnwald), Czech Republic.
  • In Romania, from Sacarımb (Nagyag), Hunyad, and Cavnic (Kapnikbanya).
  • At Sterling Hill, Ogdensburg, Sussex Co., New Jersey and Washington Camp, Santa Cruz Co., Arizona, USA.
  • In the Huallapon mine, Pasto Bueno, Ancash Province, Peru. At Bidi, Sarawak Province, Borneo.
  • In the Akatani mine, Fukui Prefecture, Japan. From the Dajishan tungsten deposits, Jianxi Province, China.

References

  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  • Mindat.org. (2019). Orpiment: Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].
  • Wikipedia contributors. (2019, June 8). Arsenic. In Wikipedia, The Free Encyclopedia. Retrieved 12:08, June 11, 2019, from https://en.wikipedia.org/w/index.php?title=Arsenic&oldid=900851916

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