The most northerly outlier of relevant lavas occurs south of the City of Aberdeen. Barras Quarry, also known as Cotbank Quarry is still a productive source situated on the southern flank of Bruxie Hill about five miles south of Stonehaven. Although not currently in use, the quarry has been worked periodically over the years since it was opened in the 1960s by the local farmer to supply road building hardcore.

Collectors have visited since that time and quantities of exceptional specimens have been removed as new material was uncovered. Currently however, the quarry has been worked out and little quality material can be found. The best and most productive area lies on the eastern side of the quarry where occasionally, as well as agates, amethyst and smoky quartz geodes have been removed. Specimens are usually blue-grey in colour but occasionally ones are found with subtle pastel shades of pink or purple. A high proportion of stones are uncracked. They also display flow bands associated with white segregation spots that give the best examples their distinctive appearance. Some can be large, up to 100mm across, although the majority are found in the range 40 to 60mm.