Answer
Hornblende, a common amphibole mineral, was the actual content of the ore discovered by Frobisher. Despite his initial belief that it was gold, further analysis revealed the true nature of the material. Hornblende is a dark, iron-rich mineral that is often found in igneous and metamorphic rocks. It is not a valuable ore, and Frobisher's expedition ultimately failed to find any significant amounts of gold or other precious metals.