Revealing mistake: After the cowboys have terrorized the village at the beginning, the girl finds her dead dog and starts crying, when she picks it up it's painfully obvious it's a stuffed toy.
Revealing mistake: In the scene just before the huge nugget Spider is holding gets shot in two, if you look closely you can see the line down the centre where the two halves break.
Answer: It's a gold nugget. It is not real gold, of course, but is a movie prop. That is why it looks like some other type of substance.
raywest ★
Or it's a piece of quartz with a lot of gold in it.