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Formula: Al2Si2O5(OH)4
Phyllosilicate (sheet silicate), kaolinite -
serpentine group, polytype of
halloysite-7Å, kaolinite and
nacrite
Crystal System: Monoclinic
Specific gravity: 2.60 measured, 2.62 calculated
Hardness: 2 to 2½
Streak: White
Colour: White, or tinted by impurities
Common impurities: Ti,Fe,Mg,Ca,Na,K
Environments
Sedimentary environments
Metamorphic environments
Hydrothermal environments
Dickite is a secondary mineral, usually of hydrothermal
origin, derived in
part from the alteration of aluminosilicate minerals; it also occurs as an authigenic (formed in place) sedimentary phase.
Chalcedony is a common associate
(Mindat, MW, HOM).
Localities
At the Francon quarry, Montréal, Québec, Canada dickite occurs as a silky white coating on
quartz
(Min Rec 37-1.30).
At the Imiter Mine, Tinghir Cercle, Tinghir Province, Drâa-Tafilalet Region, Morocco, dickite occurs as 0.2 mm
white scales with
cerussite in altered galena
(Min Rec 422.123).
At the type locality, the Pant-y-Gaseg mine, Amlwch, Isle of Anglesey, Wales, UK, dickite forms colourless to white
hexagonal
plates up to 0.1 mm across, on quartz and
dolomite
(MW).
At Aberfan, Merthyr Tydfil, Mid Glamorgan, Wales, UK, dickite in association with
nacrite
has been confirmed from the Aberfan borehole by X-ray data
(MW).
At the Fforchaman Colliery, Rhondda Cynon Taf, Wales, UK, dickite has been found coating
millerite
(MW).
At the South Wales Coalfield, Wales, UK, dickite is present in clay
ironstone
nodules found within the Coal Measures. Specimens from the following localities are present in the collections of the
National Museum of
Wales: Avon Colliery, Bryn Henllys Colliery, Coed Ely Colliery, Ferndale, Gelli Colliery, Markham Colliery, Nant Helen
Opencast,
Parc Slip West Opencast, Margam Opencast, St John’s Colliery and Wyndham Deep Colliery
(MW).
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