This is a kind of Soul Device that can be attached to a skeleton's eye socket, enhancing the outward intensity of Soul Energy, and increasing the skeleton's perception range.
Under the stimulation of a powerful soul, this release of Soul Energy could form an attack wave like thunder, hence it is called Soul Thunder.
It is part of Steadfast Locke's equipment. There are two of them, Harvey only brought out one, the other one is probably still on Locke.
Because it is a Soul Device, it can be brought into the soul, so we didn't see the other one on Locke's skeleton. It may have disappeared forever along with Locke's soul disintegration.
This Soul Device that enhances perception, one can't say it's useless, but it doesn't have much effect, no value, and can't be used for growing crops.
To offend Harvey for something that Ange is not interested in and also has no value, remembering his grudge? No way is Silver Coin that stupid.