- Chemistry: FeSO4 - 7H2O,
Hydrated Iron Sulfate.
- Class: Sulfates
- Group: Melanterite
- Uses: A very minor ore of iron and as mineral specimens.
Melanterite is one of only a few water soluble sulfate minerals. It
forms in the near-surface secondary oxidation zone of ore deposits usually
late in their development. In many mines, melanterite is an ongoing precipitate
or efflorescent forming white to green encrustations, crystal aggregates
and stalactites right on the sides of the mine's shafts. The primary source
of the iron for melanterite is iron sulfides such as
A technique for removing copper from the copper sulfate mineral
is responsible for the naming of an alternate name for melanterite. Chalcanthite,
like melanterite, is soluble in water and it thus makes a solution of copper
sulfate. If metallic iron is added to the solution, then metallic copper
precipitates, leaving a solution of iron sulfate. This left-over solution
has the same composition as a solution made from dissolving melanterite.
The alternate name for melanterite is "copperas", from
the Greek meaning "copper water", an allusion to the left-over
solution. In a way, this could be thought of as "copper-providing
Attractive crystals of melanterite with a beautiful blue-green color
are know to exist and are sought after. The shades toward blue come from
impurities of copper which can substitute for as much as one third of the
iron. The more copper, the bluer the crystals. Generally melanterite is
known as having a white or green color.
Melanterite is also the name of a group of only five monoclinic sulfates
of which melanterite is the only somewhat common member. Members of this
group have the same basic structure as melanterite, but can have in place
of iron, ions of manganese, zinc, cobalt and copper.
These are the members of the Melanterite Group:
(Hydrated Cobalt Sulfate)
(Hydrated Copper Sulfate)
(Hydrated Manganese Sulfate)
- Melanterite (Hydrated Iron Sulfate)
(Hydrated Zinc Copper Iron Sulfate)
- Color is white, green, yellowish green or blue-green.
- Luster is vitreous to silky.
- Transparency: Crystals are translucent to slightly transparent.
- Crystal System is monoclinic; 2/m.
- Crystal Habits include stubby prismatic or blocky to tabular
crystals, sometimes as pseudo-octahedrons. Also acicular, fibrous and capillary
and found as encrusting, stalactitic and concretionary masses.
- Cleavage is perfect in one direct but only distinct in another.
- Fracture is conchoidal.
- Hardness is 2
- Specific Gravity is approximately 1.9 (well below average).
- Streak is white.
- Other Characteristics: Is soluble in water and may deteriorate
with absorption of water. The taste has a sweet, astringent and metallic
- Associated Minerals are
- Notable Occurrences include Minas de Rio Tinto, Spain; Rammelsberg,
Harz Mountains, Germany and Falun, Sweden; and in the United States at
Ducktown, Tennessee; South Dakota; Colorado; Bigham Canyon, Utah; Comstock
Lode, Lincoln County, Nevada; Butte, Montana; at several mines in Arizona
and at The Geysers in Sonoma County and at Leona Heights, Alameda County,
- Best Field Indicators are crystal habit, low density, associations,
solubility in water, taste and color.