Click the microscope button to view a thin section for this sample.
Click the object button to view an object rotation for this sample.

Fact sheet


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:

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


Additional images
  • Psilomelane 12 cm across
  • Psilomelane 12 cm across
  • Psilomelane 6 cm across
  • Psilomelane 10 cm across
  • Psilomelane 6 cm across
  • Psilomelane 12 cm across
50.572016, -4.465665
About this collection

This Collection focuses on Cornwall and West Devon’s mineralogical and mining heritage.  The specimens it features are drawn from the collection of the Royal Institution of Cornwall (RIC) held at the Royal Cornwall Museum (RCM). 

This collaborative project involving the RCM, the Cornish Mining World Heritage Site and The Open University explores how access to the RIC’s mineral collection and the stories it can tell can be widened using digital technology.  It includes radioactive minerals from Cornwall that would otherwise be inaccessible to the public for health and safety reasons.

Sample details

Category guide  
Category Guide
Refers to any word or phrase that appears in the individual rock names. Names are generally descriptive; they allow users to search for broad terms like ‘granite’ as well as more specific names such as ‘breccia’. However, the adjacent descriptions of the specimens captures a wider range of general words and phrases and is a more powerful search tool.
Refers to any word or phrase that appears anywhere in the descriptions of the specimens
Accessory minerals
Minerals that occur in very low abundance in a rock. They are usually not visible with the naked eye and contribute perhapssver, they often dominate the rare elements such as platinum group metals.
Rock-forming minerals
Minerals that make up the bulk of all rock samples and are also the ones used in rock classi?cation.
Selecting one or more period, for example 'Jurassic'.
A term used to group together related samples that are not already gathered into a single Collection. For instance, there is a ‘SW England granites’ theme that includes such rock types as granite, hydrothermal breccia, skarn and vein samples.
A general term used to label a rock sample. It is a useful way of grouping similar samples throughout a collection. Category names are often, but not exclusively, common rock names (e.g. granite, basalt, dolerite, gabbro, greisen, skarn, gneiss, amphibolite, limestone, sandstone).
The owner of the sample that appears in the collection. For example, NASA owns all the samples that appear in the Moon Rocks collection
We would like to thank the following for the use of this sample: