Large Cut and Polished Banded Agate Bowl

Placenticeras costatum with gem quality fossilised shell with some visible suture lines, conserved and stabilised with natural polish and acrylic lacquer, with excellent iridescence showing red, green, orange and gold colours. 952 grams, 26 cm



Found St Mary River Valley, Lethbridge Mining District, Alberta, Canada. Property of a Bristol, UK, gentleman collector. Accompanied by a certificate of authenticity, exportable under Moveable Cultural Property Permit no.7021-25-12-22-0102.

The striking iridescence of these ammonites from Alberta, Canada, termed 'ammolite', was given the status of a gemstone by CIBJO in 1981. An iridescent opal-like play of colour is shown in fine specimens, and is caused by the microstructure of aragonite, the same mineral contained in pearls and nacre. The thicker the structural layers, the more reds and greens are produced; the thinner the layers, the more blues and violets predominate. The ammonites are a group of molluscs that lived in the seas from the mid-Devonian (approximately 400 million years ago) to the end of the Cretaceous (65 million years ago). The sequence of events that famously killed off the dinosaurs also drove the ammonites to extinction.

Diplomystus sp. fossil fish on a matrix slab showing good detail to the spine and ribs. 18 kg, 58.5 x 46 cm



From Wyoming, USA. From a Cambridgeshire, UK, collection.

On a curving matrix and showing good detail, especially on the scales. 557 grams, 21.2 cm



From Cheddar, Somerset, UK. From the private collection of Kenneth Machin (1936-2020), Buckinghamshire, UK; his collection of antiquities and natural history was formed since 1948; thence by descent.