There are not that many UK minerals to be found with a species name beginning X.
Here is one classic example recently listed on e-Rocks by Mike Brooke, Broadstone Minerals.
Classic and interesting locality specimen from Wheal Maudlin, Lanlivery, Cornwall - ex Michael Bates Collection.
From Mike's description:
Size: H:5.5cm x W:3.5cm x D:2.4cm
Description
Kahki coloured matrix with a rich layer of radiating xanthosiderite over one surface. displays well.
