Psilomelane
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Description: 

Psilomelane is a group name used for undifferentiated black manganese oxides, the main mineral group from which the metal manganese is obtained.

Cornwall produced only small amounts of manganese. Most came from Ruthers mine, near St Columb Major and the rest from mines in the area around Launceston.

This specimen of stalactitic psilomelane came from Trebartha Lemarne mine, SW of Launceston. It was bought by the Royal Institution of Cornwall (RIC) from Lostwithiel-based mineral dealer Richard Talling in the early 1860s. Talling was one of the most significant mineral dealers in Cornwall; his handwritten number tag ‘4.’ can still be seen on this specimen. The printed labels refer to the RIC’s catalogue of its metallic minerals, compiled by Cornish mineralogist J H Collins, which was published in 1881.

Chemical analysis at the Open University in 2013 indicates that this mineral is actually the species romanèchite.

Generalised chemical formula:
Ba(Mn2+)(Mn4+)8O16(OH)4

Specimen no. TRURI: 801.3142
Location: Trebartha Lemarne, SW of Launceston
Grid Reference: SX 255 776

Mindat http://www.mindat.org/min-3304.html

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In Time
Accuracy:
Location precision: 
Good
Timescale:
Not known
Ma = Millions of years ago
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mineral
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