I understand this to be a Spanish Pillar, possibly minted in Mexico as it has the Mo- MF mintmarks and which is 96.8 grams of .91.7% silver, known as a piece of 8 (8 reales). These coins were of the first to be uniformly minted and were used as the main currency in the colonies before the revolution and up until the United States started making it's own currency in the early 1800s.