Crystal System: Amorphous
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Manganese iron silicate hydrate
Chemical Formula: (Mn,Fe)(SiO)3•H2O
Method(s) of Verification: not known.

Chemical Group:

  • Silicates

Geological Context:

  • Hydrothermal
Introduction: neotocite is a black, amorphous, secondary mineral, with a resinous lustre, which forms by the alteration of manganese minerals such as rhodonite or other manganese silicates. It is found in manganese deposits of a volcanogenic-sedimentary origin.
Occurrence in Wales: neotocite is known from just one locality in Wales. The amorphous nature of this mineral does not assist its identification as verification by X-ray diffraction is not possible.

Key Localities:

  • Nant Mine, Nant-y-Gadwen, Rhiw, Llŷn, Gwynedd: a specimen in the mineral collection of the National Museum of Wales, from Nant Mine (NMW 27.111.GR.444), consists of dark brown to black, vitreous neotocite, with a conchoidal fracture. This specimen was originally collected by G.J. Williams and identified by L.J. Spencer. Clark et al. (1978) also describe a neotocite specimen collected from the No. 2 Level at the mine, one of four originally collected by Sir Arthur Russell in 1911. The neotocite is massive, black to resinous and breaks into dark olive-green to brown translucent fragments.


  1. Clark, A.M., Eaton, A.J., Jones , G.C. & Mount, M., 1978. A study of the neotocite group. Mineralogical Magazine, 42, M26-M30.