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)

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)

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
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
écrinsite
edenharterite
ferrofettelite
hyršlite
jasrouxite
jentschite
luboržákite
protochabournéite
raberite
sicherite
sinnerite
tsugaruite
twinnite
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

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

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
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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