Melanterite
Melanterite is one of only a few water-soluble sulfate minerals. It is the iron analog of Chalcanthite. Melanterite is a hydrated iron sulfate mineral formed after the decomposition of pyrite or other iron minerals due to the action of surface waters. It is often found in mines as a post-mining formation on mine walls as encrustations or stalactites. It is subject to dehydration and may dehydrate the mineral Siderotile. Some specimens may have a beautiful blue-green color and may be fairly transparent. Faceted gems are very rare and are extremely difficult to cut due to the softness (Mohs 2.0) and water solubility. Gems should be stored in an airtight container since they may be subject to dehydration. Melanterite should be handled with caution because of the possible presence of sulfuric acid.
Melanterite occurs at many localities, a few with large crystals. In Germany, from the Rammelsberg mine, near Goslar, Harz Mountains. At Falun, Sweden. From Rio Tinto, Huelva Province, Spain. At Idria, Slovenia. Large crystals on the island of Cyprus. From Cantiere Conche, Elba, Italy. At Baia Sprie (Felsóbánya), Romania. From Damar, Murgul, northeast Anatolia, Turkey. In the USA, at the Alma mine, Leona Heights, Alameda County, and the Island Mountain mine, Trinity County, California; from Ducktown, Polk County, Tennessee; at Butte, Silver Bow County, Montana; in the Lucky Boy mine, Bingham district, Salt Lake County, Utah. At volcanoes on the Kamchatka Peninsula, Russia. From Tierra Amarilla, southeast of Copiapó, Atacama, Chile.
| Category: | Sulfate mineral |
| Chemical Formula: | Fe2+(SO4)•7(H2O) |
| Hydrated Iron Sulfate | |
| Molecular Weight: | 278.02 gm |
| Composition: | Iron | 20.09 % | Fe | 25.84 % | FeO |
| Hydrogen | 5.08 % | H | 45.36 % | H2O | |
| Sulfur | 11.53 % | S | 28.80 % | SO3 | |
| Oxygen | 63.30 % | O | |||
| 100.00 % | 100.00 % | = TOTAL OXIDE |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | Crystals are rare, equant, pseudo-octahedral, to short prismatic [001], showing {120}, {001}, may be thick tabular {010}, {102}, many smaller modifying forms, to 20 cm; commonly stalactitic, in concretions and crusts, massive, pulverulent, and as efflorescences. |
| Twinning: | None |
| Cleavage: | On {001}, perfect; on {120}, distinct |
| Fracture: | Conchoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 2.0 |
| Density: | 1.895 – 1.898 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Other: | Soluble in water. May dehydrate to the mineral Siderotile. |
| Health Warning: | CAUTION: Poisonous! May contain sulfuric acid. Do not lick or ingest. Do not touch with bare hands or wash hands immediately after handling! |
| Color: | Green, pale Green, Greenish Blue, Bluish Green, Colorless; Colorless to pale Green in transmitted light. |
| Transparency: | Transparent to Translucent, Opaque |
| Luster: | Vitreous |
| Refractive Index: | 1.470 – 1.486 Biaxial ( + ) |
| Birefringence: | 0.0150 – 0.0160 |
| Dispersion: | None to Weak; inclined, r > v |
| Pleochroism: | None |
