Orbicular granite from Mt. Farmer, Western Australia

Orbicular granites are spectacular geological enigmas. They occur from place to place as small pods, trains, bands, lenses, pipes and patches, not uncommonly along or close to margins of granitic intrusions. They occur on all continents in rocks of many ages. Orbicular granites are so fascinating geologically because of the structural complexities and variations in mineral composition within and between individual deposits. Significantly, even though orbicular structures have been recorded in many rock types from a wide range of physical and tectonic settings, no two orbicular granite occurrences are alike.

……One significant feature of the 2.6 b.y. old Mt. Farmer orbicular granite is its overall freshness. In this aspect it is unlike most orbicular granites which are characteristically substantially altered by the large amount of magmatic water associated with its formation, or by subsequent hydrothermal activity. This freshness translates to a polished finished quality which is at least very good.

…….Many factors contribute to a compelling and instant appeal for this exotic stone including its freshness, variation in orbicule morphology, variation in mineral composition from one orbicule layer to the next and from orbicule to orbicule, variation in the ratio between orbicules and “groundmass granite”, and the intimate relationship in places between the orbicular granite and commonly associated post-emplacement features. Add to this a scattering of large gemstone quality titanium minerals and very rare pockets of complex sulphide intergrowths. The nett product is a spectacular rock of unsurpassed 3-dimensional visual effect guaranteed to promote endless conversation, argument and speculation.