Alacranite
As8S9 [CNMNC approved formula]
Named for the occurrence in the Alacran deposit, Chile.
IMA status : | Approved Species 1985 (IMA1985-033) |
CLASSIFICATION | |
Dana (8th edition) : |
02.08.22.04 |
(02) Sulfides - Including Selenides and Tellurides | |
(02.08) where Am Bn Xp, with (m+n):p=1:1 | |
(02.08.22) Realgar Series | |
Nickel-Strunz (10th edition) : |
02.FA.20 |
(02) Sulfides | |
(02.F) Sulfides of Arsenic, Alkalies; Sulfides with Halide, Oxide, Hydroxide, H2O | |
(02.FA) With As, (Sb), S | |
Crystal system: | Monoclinic System |
Point group (H-M): | 2/m — prismatic |
Unit cell: | a = 9.89 Å, b = 9.73 Å, c = 9.13 Å, b = 101.84° |
Crystal Habit: | Grains flattened and prismatic, to 0.5 mm |
Color: | Orange-yellow, orange |
Diaphaneity: | Transparent |
Luster: | Adamantine, greasy |
Hardness (Mohs): | 1.5 |
Measured Density: | 3.43 g/cm3 |
Cleavage: | Imperfect on {100} |
Tenacity: | Very brittle |
Fracture: | Conchoidal |
Streak: | Orange-yellow |
Polymorphism and Series: | Trimorphous with pararealgar and realgar. |
Geologic Setting: | In hydrothermal As–S veins (Alacran mine, Chile); in the condensation zone of a hydrothermal Hg–Sb–As system as cement in a sandy gravel (Uzon caldera, Russia); formed at low temperatures in a polymetallic hydrothermal deposit on a submarine seamount (Conical Seamount, Papua New Guinea). |
Mineral Association: | Realgar, orpiment, arsenic, sulfur, stibnite, pyrite, greigite, arsenopyrite, arsenolamprite, sphalerite, acanthite, barite, quartz, calcite (Alacran mine, Chile); realgar, orpiment, uzonite, stibnite, cinnabar, pyrite, sulfur (Uzon caldera, Russia); realgar, pyrite, sphalerite, galena, chalcopyrite, amorphous silica (Conical Seamount, Papua New Guinea). |

Sample size: 3.8 x 4.3 x 2.8 cm
Photo: Dan Weinrich
