thunderstone

1. Any of various mineral concretions, such as a belemnite, formerly supposed to be thunderbolts.
2. Archaic. A flash of lightning conceived as a stone; a thunderbolt.

When a particularly loud crack of thunder was heard, it was thought that something more than mere lightning had buried itself in the ground; certain unusual objects found in the earth were popularly called ‘thunderbolts’ or ‘thunderstones’, including fossil belemnites, sea-urchins, and, more rarely, ammonites, pointed quartz crystals, lumps of iron pyrites, and Neolithic stone axes. On the principle that lightning never strikes the same place twice, their presence was thought to protect a house. In Sussex in the early 20th century fossil sea-urchins were set on the outside windowsills of kitchens and dairies to stop milk going sour, because thunder was believed to ‘turn’ milk; ammonites were used in the same way in Wiltshire and Gloucestershire in the 1860s, and it was noticed that mischievous village boys never interfered with them, simply because they were thunderbolts. Examples of all these objects could be found in London street markets in the late 19th and early 20th centuries, on sale under this name (Lovett, 1925: 49-51).

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