Crystal System: Orthorhombic
Status of Occurrence: Confirmed Occurrence
Chemical Composition: Barium aluminium silicate hydrate
Chemical Formula: BaAl2Si3O10.4H2O
Method(s) of Verification: Benallt Mine - XRD at the National Museum of Wales (XRD numbers NMW X-1608 & X-1611); Dolyhir Quarry - XRD at the National Museum of Wales (XRD no. NMW X-1861).
Glassy, wedge-shaped edingtonite crystals with prismatic harmotome from Dolyhir Quarry, Old Radnor, Powys. Field of view is 4 mm across. © National Museum of Wales.
Introduction: edingtonite is a rare mineral which forms in cavities in mafic igneous rocks and nepheline syenites. It also occurs in hydrothermal veins.
Occurrence in Wales: edingtonite occurs as a minor component of sugary white veinlets cutting massive analcime at Benallt manganese mine at the southern end of Pen Llŷn (T.F. Cotterell, unpublished data). Distinct wedge-shaped microcrystals have more recently (July 2007) been discovered at Dolyhir Quarry, near Old Radnor in the Welsh Borderland (Cotterell et al., 2011).
- Benallt Mine, Llŷn, Gwynedd: semi-quantitative XRD analysis of sugary white veinlets cutting massive creamy analcime indicates that 3-6 % edingtonite is present associated with major analcime, banalsite and minor harmotome (T.F. Cotterell, unpublished data).
- Dolyhir Quarry, Old Radnor, Powys: sub mm sized, glassy, characteristic wedge shaped crystals, have been identified in an altered dolerite dyke exposed briefly in 2007. Abundant core-bit twinned prismatic harmotome crystals occur in association (Cotterell et al., 2011).
- Cotterell, T.F., Green, D.I., Hubbard, N., Mason, J.S., Starkey, R.E. and Tindle, A.G., 2011. The Mineralogy of Dolyhir Quarry, Old Radnor, Powys, Wales. UK Journal of Mines and Minerals, 32, 5-61.