The Isle of Mull is legendary among agate collectors. I first visited this location in 1993, and found an inconsequential agate at Carsaig embedded in the black andesite. Many years later in 2014 I visited the location with partner in tow and during June of that year and the following May, proceeded to search areas at Carsaig, Port Nan Droughan and Burg for agates.
As has been noted these locations are difficult and long of access. Port Nan Droughan is a former settlement with ruined schoolhouse still extant, and can be best accessed from Scoor which is still a good 4 or 5 miles away. The beach itself is almost inaccessible, and it was only after an incident with a local adder and the exploration of a nearby stream that we were able to get to the rocky shore at all. The rocks are punctuated by areas of beautiful white sand, a speciality of the area, and this place is truly one of the most gorgeous beaches in Scotland. In my experience, agates were quite difficult to find here, and generally average in appearance, displaying blue-grey fortification patterns. I have heard that larger agates measuring 15 centimetres can be found here, but from what I have seen these are most likely vein agates within the matrix, and generally unremarkable. Agates can be found in the area of the famous "Carsaig Arches", but sparingly and considerable effort must be made to explore the area on foot. Examples can also be found at Carsaig itself, but again they are sparsely distributed. Scoor occasionally turns up agates in the areas of shingle framing the numerous sandy bays in the area, these are generally small and grey and occasionally show onyx banding. At Burg, again access to the shingle beaches is difficult and hazardous, yet fine fortification agates can be found here. Close to the Fossil Tree agates of a very blue colouration may be found, but again procuring exceptional specimens of this species is difficult due to the tide,weather, and location, which is almost 7 miles from the road.
At the aforementioned Carsaig Arches remarkably marked agates can be found. I refer to stones of the whorled variety, first noted by the indefatigable and towering Jock Nimlin. Did Jock discover these agates in the 1970s? It's possible, but unlikely he was the first. Others have amassed comprehensive collections of whorled stones since then, through intensive collecting over many years. Few photographs of stones from these collections exist. Although generally whorled agates from Carsaig tend to be of the usual grey-blue colour, sometimes specimens are found in light brown or yellowish tones, even occasionally in lilac or violet. These variations in colour occur with other varieties of agate in other locations on Mull.
I myself have only been to the Carsaig Arches area twice. I did my best to search thouroughly and cover as many likely places as possible, but there seems to be only one beach that is largely the most productive, despite the shingle extending all the way to Port Nan Droughan. It is this place I will return to.
Stalactitic, sagenitic and Onyx agates have been found here, but generally Mull agates stick to a fortification pattern. Exceptional agates of the aforemnentioned types are only found through extensive and prolonged searching. Whorled agates are fairly common at their location but again tend to be average to the species, as opposed to the rarely found and highly contrasted (in light grey-blue and black) nodules.
So, generally the finest agates from Mull are reserved to those individuals privileged to live in the area, with the time and resources available to visit the most productive locations during the winter and spring months when storms have caused the greatest movement of shingle. The best that the rest of us can hope for (and I have seen whorled agates of 7cm) is serendipity>