A 9th example is published (also as a trefoil brooch) in Benet's second edition Artefacts of England & the United Kingdom - current values (2003) page 315, item no.: V-07-0202.
Ironically - as mentioned in the article - the trefoil mount from Hafurbjarnarstadir, Iceland was from a pagan burial where it was clearly worn in typical Scandinavian fashion as a brooch, with textile surviving attached to the lugs on its back. But this must have been a so called secondary use form. The Icelandic example aslo had an additional perforation through one of its arms, wich may suggest that the trefoil was worn as a pendant at some stage.
Just under 10 known examples - to me at least ! - a rare kind of viking artefact..
But who's counting ?
A real trefoil brooch..
Bronze, 8.50 grams; 38.53 mm. Circa late 9th - early 10th Century A.D. An extremely rare type of English Viking brooch (see ref.: a number of 43 in England is recorded until know) in an excellent state of preservation.
Most of these type of brooches are found as segments, broken due to choise of material or soil conditions.
This example has a very clear deep incised line decoration with a central triangle at the junction of the arms, with conventionalised plants derived from imported western European trefoil mounts These three tree-like objects form the outer decoration to form a spectacular design and an amazing piece of art. Complete with catch plate and perforated hinge plate on the reverse.
Found in Norfolk.
Ref.: Viking identities, Scandinavian Jewellry in England by Jane F. Kershaw (2013) page 79-91 Trefoil brooches, page 82-83 trefoil brooches with geometric decoration (Type G) Fig. 3.43
Image beneath: after the brooch had been cleaned professionally
Brooches of this type were used to fasten a cloak or shawl on the breast. The form is modelled on Carolingian trefoil fittings from sword-belts of the ninth century, presumably either seized by the Vikings in raids on the Continent, or perhaps obtained peacefully through trade or the exchange of gifts. The decoration, however, uses animal rather than plant motifs, a style with which the Vikings were familiar. Simpler versions appear to have been mass-produced.