World's largest rough gem diamond was found with a pocket knife in 1905

In 1905, mine manager Frederick Wells spotted a glint in a South African mine wall and extracted a 3,106-carat diamond using his pocket knife. Named Cullinan, the rough stone remains the largest gem-quality diamond ever discovered. Its largest polished gem, the 530.2-carat Great Star of Africa, now adorns Britain's Sovereign's Sceptre with Cross, part of the Crown Jewels.