Also, tinier granite particles are common along the eastern sandy shore. With the water current, it would be possible for the rock to arrive at the destination at which it was found. In my opinion the rock is a chert concretion. In this case it is composed of fine-grained chalcedony and quartz. The outer shell seems to be composed of limestone, from which the concretion has been weathered away.
Similar concretions are common for example in Egypt in the Valley of Kings.
A European film group brought them here in Finland some years ago. They thought they were tektites formed in giant meteorite impacts. My laboratory study, however, showed them as chert concretions weathered from the nearby limestones. These concretions were called as Faroe's Eyes. At first glance, it appears as a possible fossil of an egg, perhaps from a past dinosaur.