Mynydd Nodol Mine, Mynydd Nodol, Llanycil, Gwynedd, Wales, UK

An extremely large and fine example of the relatively high-grade botryoidal manganese ore mined at Mynydd Nodol during the mid-to late-19th century but which simply did not occur in sufficient quantity for the mine to become profitable. The botryoidal bed on this piece reaches 5 cm in thickness and side-on in cross-section forms compact concentric ...

© Tom Cotterell

Aggregate of botryoidal hollanite. Specimen 35mm wide, with individual botryoids typically 3-4mm in diameter. Collected 2006, Ian Jones collection,

© ian jones

NOTE!- Mineral has been brass brushed giving brassy finish, originally Sub-Metallic Black. Botryoids around 2mm-4mm.

© JamesHutchins

A slightly more unusual form of hollandite-cryptomelane from Mynydd Nodol Mine. Cauliflower-like florets (but black) of complex zoned layered botryoidal hollandite-cryptomelane. SEM-EDS studies of material from this find reveal complex repeated chemical zonation from barium (hollandite) and potassium (cryptomelane) on a microscopic scale ...

© Tom Cotterell

Dark grey to black botryoidal hollandite-cryptomelane. This material is rhythmically zoned in layers but it is almost impossible to know which layer is which in hand specimen. In polished section under a Scanning Electron Microscope (SEM) the bands are very distinct from bright white (dense) hollandite to darker grey (less dense) cryptomelane. ...

© Tom Cotterell

Shiny metallic grey prismatic microcrystals of pyrolusite sat upon hollandite-cryptomelane in cavities within massive colloform compositionally zoned hollandite-cryptomelane. Pyrolusite crystals are very rare from this site, most material being mixed hollandite/cryptomelane. Collected May 2018.

© Tom Cotterell

A huge, dramatic display specimen of the remarkable botryoidal zoned hollandite-cryptomelane from Mynydd Nodol Mine. The hard, dense, compact botryoids look homogeneous, but are anything but. In polished section sub-mm scale repeated compositional zoning from hollandite to cryptomelane and back again shows up by density under SEM backscatter ...

© Tom Cotterell

A much more 'bubbly' form of the hard, compact botryoidal intergrown hollandite-cryptomelane from Mynydd Nodol Mine. This material consists of complex repeated shifts in chemistry from hollandite to cryptomelane and back, but this can only be seen using scanning electron microscopy (SEM). Duplicate material has been been studied in detail using ...

© Tom Cotterell