There are three islands in the Western Isles of Scotland where agates can be found, they are Mull, Iona, and Rhum. The lava formed here is vastly different to that on the mainland (much younger on the Isles) and as such the agates here are also different, particularly in their colouration as you will see in the following examples.
The agates on Mull are often a very pale cream colour ,with veins of white or grey chalcedony. The combination of agate veins mixed with the fortification banding makes these agates stand out and they are highly collectible. The unfortunate part of collecting these agates is they are mainly in remote locations across the island, so rock scrambling is essential if any success is to be had!
On Iona the agates are usually much smaller than those found on Mull, and are usually blue/grey in colour. Iona interestingly has no agate bearing lavas, and it is thought that the agates found here come from Mull centuries ago carried on ice flows. If the theory was ever proved it must mean that somewhere on Mull there are coloured agates.
Rhum is not easy to visit as an island and is managed as a nature reserve by its owners the Nature Conservancy Council. Any collecting done on the island must have the permission of the council from their Inverness headquarters. The agates are very similar to those found on Mull and Iona. The main difference between the stones found on these isles, is that bloodstone can be found in certain localities on Rhum.