Psilomelane
A group of hard black manganese oxides used as ore.
Psilomelane is a group name for hard black manganese oxides, including hollandite and romanechite. It consists of hydrous manganese oxide with variable amounts of barium and potassium, and has no definite chemical composition. It is erroneously, and uncommonly, known as black hematite, despite not being related to true hematite, which is an iron oxide.
- field
- Mineralogy
- known_for
- Common and important ore of manganese
- hardness
- 5 to 6
- specific_gravity
- 3.7 to 4.7
- streak
- Brownish black
Lore & Background
Psilomelane occurs as botryoidal and stalactitic masses with a smooth shining surface and submetallic lustre. Its streak is brownish black and the fracture smooth. The mineral often contains admixed impurities, such as iron hydroxides, and is soluble in hydrochloric acid with evolution of chlorine gas.
Reader's Guide
Psilomelane is a common and important ore of manganese, occurring under the same conditions and having the same commercial applications as pyrolusite. It is found at many localities, including the Restormel iron mine at Lostwithiel in Cornwall, Brendon Hills in Somerset, Hoy in Orkney, Sayn near Coblenz, Hout Bay near Cape Town, and Crimora in Augusta county, Virginia. With pyrolusite it is extensively mined in Vermont, Virginia, Arkansas, and Nova Scotia. Its generalized formula may be represented as Ba(Mn2+)(Mn4+)8O16(OH)4 or as (Ba,H2O)2Mn5O10, though it is sometimes considered to be a hydrous manganese manganate of doubtful composition. The amount of manganese present corresponds to 70-80% of manganous oxide with 10-15% of available oxygen. The mineral is readily distinguished from other hydrous manganese oxides (manganite and wad) by its greater hardness of 5 to 6.
Did You Know?
- Psilomelane is erroneously, and uncommonly, known as black hematite, despite not being related to true hematite.
- Psilomelane has no definite chemical composition and occurs as botryoidal and stalactitic masses.
- It is soluble in hydrochloric acid with evolution of chlorine gas.
Frequently Asked Questions
What is Psilomelane?
Psilomelane is a collective name for a family of hard, black manganese oxide minerals that includes species such as hollandite and romanechite. It is a hydrous manganese oxide with variable barium and potassium content, and it has no single fixed chemical formula.
What is Psilomelane used for?
Its main significance is as a common and economically important ore source of manganese. Rather than being prized as a gem or collector specimen, it is valued industrially for the manganese it yields.
What does Psilomelane look like and how hard is it?
It appears as a hard, black mineral with a brownish-black streak and a specific gravity between roughly 3.7 and 4.7. On the Mohs scale it rates 5 to 6, placing it in the moderately hard range for a manganese oxide.
Is Psilomelane the same as black hematite?
No—labeling it "black hematite" is a well-known but incorrect misnomer. True hematite is an iron oxide, while Psilomelane is a manganese oxide, so the two are chemically unrelated despite the overlapping dark appearance.
What is the chemical composition of Psilomelane?
Because it is a group name rather than a single mineral species, Psilomelane has no definite chemical formula. It is essentially hydrous manganese oxide containing fluctuating amounts of barium and potassium that vary from sample to sample.
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