E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Nugget of Gold.
Nugget, a diminutive of nug or nog, as logget is of log. A nog of sugar (Scotch) is a lump, and a nugget of gold is a small lump. So a log of wood is a billet (Latin, lignum), and loggets (Norfolk) are sticks of toffy cut up into small lumps.
A correspondent in Notes and Queries says nog is a wooden ball used in the game of shinney. Nig, in Essex, means a piece; and a noggin of bread means a hunch.