Arsenic

cinnabar

realgar

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Formula: As
Native element, arsenic group, trigonal paramorph of orthorhombic arsenolamprite and pararsenolamprite, also orthorhombic, forms a series with antimony
Crystal System: Trigonal
Specific gravity: 5.6 to 5.8
Hardness: 3½
Streak: Tin-white
Colour: Tin-white, tarnishing to dark grey or black
Solubility: On heating arsenic sublimes without melting
Common impurities: Bi,Sb,Fe,Ni,Ag,S,Se
Environments:

Hydrothermal environments

Arsenic occurs in hydrothermal veins and deposits that contain other arsenic minerals, sometimes in cobalt-silver sulphide veins (HOM). It oxidises slowly in air and is then covered with a thin crust of tiny arsenolite crystals (Mindat). Associated minerals include arsenolite, cinnabar, realgar, orpiment, stibnite, galena, sphalerite, pyrite and baryte. (HOM)

Localities

At Llallagua, Bolivia, arsenic has been identified in a specimen consisting of alternating lamellae of native arsenic, realgar and gypsum, probably formed by the oxidation of arsenopyrite. (MinRec 37.2.126)

At Johanngeorgenstadt, Erzgebirgskreis, Saxony, Germany, native arsenic as reniform masses was encountered particularly in the Gnade Gottes tunnel. Galena crystals perched on native arsenic were found at the Gottes Segen mine. In many of the ore veins, arsenic is associated with proustite, less commonly with native silver. Cobalt and nickel arsenides can also be associated, as well as pitchblende. In areas of the veins exposed to oxidation, arsenolite and pharmacolite have formed on native arsenic (MinRec 55.5.588).

Arsenic-bearing minerals include:

Alloys
paradocrasite
törnroosite
vincentite

Arsenides - the arsenide anion is As^3-

Antimonides - the antimonide anion is Sb^3-
stibarsen

Sulphides - the sulphide anion is S^2-
alacránite
arsenopyrite
bonazziite
cobaltite
duranusite
getchellite
glaucodot
hollingworthite
lautite
irarsite
osarsite
pääkkönenite
paradimorphite
platarsite
realgar
ruarsite
vinciennite
vozhminite
wakabayashilite

Sulpharsenites - sulphide minerals which include arsenic replacing sulphur as an anion

Selenides - the selenide anion is Se^2-
kalungaite

Sulphosalts - complex sulphide minerals with the general formula A_mB_nS_p, where A represents a metal, B usually represents a semi-metal such as arsenic, and S is sulphur or rarely selenium or/and tellurium (Wiki).
argentoliveingite
arsenmarcobaldiite
billingsleyite
boscardinite
chaméanite
daomanite
écrinsite
edenharterite
ferrofettelite
hyršlite
jasrouxite
jentschite
luboržákite
parasterryite
protochabournéite
raberite
sicherite
sinnerite
tsugaruite
twinnite
veenite
watanabeite

Sulpharsenates - sulphosalts where arsenic substitutes for a metal cation
enargite
luzonite

Sulphantimonates - sulphosalts where antimony substitutes for a metal cation
famatinite

Oxides - the oxide anion is O^2-
arsenolite
claudetite
garpenbergite
karibibite

Bromides the bromide anion is Br^-
ermakovite

Carbonates - the carbonate anion is (CO₃)^2-
claraite

Tellurates - salts of telluric acid H₆Te⁶⁺O₆
dugganite

Tellurites - the tellurite anion is (Te⁴⁺O₃)^2-
eurekadumpite
juabite

Chromates - the chromate anion is (CrO₄)^2-
fornacite

Arsenates - the arsenate anion is (As⁵⁺O₄)^3-

Hydrogen Arsenates - the hydrogen arsenate anion is (As⁵⁺O₃OH)^2-
bayldonite
chudobaite
cobaltkoritnigite
dussertite
ferrarisite
fluckite
geminite
guérinite
haidingerite
naalasite

Antimonates - the antimonate anion is (Sb⁵⁺O₃)^-
manganostibite

Arsenites - the arsenite anion is (As³⁺O₃)^3-
asbecasite
cafarsite
dixenite
finnemanite
gebhardite
leiteite
ludlockite
magnussonite
reinerite
rouseite
schneiderhöhnite
seelite
trigonite
trippkeite
zimbabweite

Molybdates - the molybdate anion is (Mo⁶⁺O₄)^2-
betpakdalite

Nesosilicates - insular (Si⁴⁺O₄)^4- groups
arrheniusite-(Ce)
vicanite-(Ce)

Sorosilicates - (Si⁴⁺O₂O₇)^6- groups
arsenmedaite
tiragalloite

Phyllosilicates - (Si⁴⁺₂O₅)^2- groups
nelenite

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