Argentopyrite
AgFe2S3 [CNMNC approved formula]
Named for its composition and physical similarity to pyrite.
| IMA status : | Valid species (Pre-IMA 1866) Grandfathered |
| CLASSIFICATION | |
| Dana (8th edition) : |
02.09.13.02 |
| (02) Sulfides - Including Selenides and Tellurides | |
| (02.09) where Am Bn Xp, with (m+n):p=1:1 | |
| (02.09.13) | |
| Nickel-Strunz (10th edition) : |
02.CB.65 |
| (02) Sulfides | |
| (02.C) Metal Sulfides, M:S = 1:1 (and similar) | |
| (02.CB) With Zn, Fe, Cu, Ag, etc. | |
| Crystal system: | Tetragonal System |
| Point group (H-M): | 4/m — dipyramidal |
| Unit cell: | a = 6.64 Å, b = 11.46 Å, c = 6.45 Å |
| Crystal Habit: | Minute pseudo-hexagonal crystals |
| Twinning: | pseudo-hexagonal twins parallel [100] by interpenetration of {120}, lamellar twinning also present |
| Color: | Steel-grey to tin-white; tarnishes bronze-brown, green |
| Diaphaneity: | Opaque |
| Luster: | Metallic |
| Hardness (Mohs): | 3.5 - 4 |
| Measured Density: | 4.25 g/cm3 |
| Tenacity: | Brittle |
| Fracture: | Uneven |
| Polymorphism and Series: | Dimorphous with sternbergite |
| Geologic Setting: | Rare in silver-bearing hydrothermal veins. |
| Mineral Association: | Arsenic, proustite, pyrargyrite, pyrostilpnite, xanthoconite, sternbergite, stephanite, pyrite, nickel-skutterudite, dolomite, calcite, quartz |
This specimen contains several crystals of argentopyrite to about 1 mm showing cyclic twinning producing stout pseudohexagonal crystals with a violet tarnish. The pryramidal terminations are sometimes rough - but not all are rough, some are perfect. The sternbergite is also fabulous as thick tabular, striated crystals to 1 mm with a goldish tarnish. It is obviously much softer than the argentopyrite and foil like.Origin: Jáchymov, Erzgebirge, Západoèeský Kraj , Bohemia, Czech Republic
Sample size: 3.5 x 3 x 2.3 cm
Photo: Tom Loomis
(zoom-in of above)