A great discovery in the Jagersfontein Mine caused the most dramatic moment in the mine's history. On the evening of June 30th, 1893, an African picked up an immense diamond in a shovel of gravel which he was loading into a truck; he hid it from his overseer and delivered it directly to the hands of the Mine Manager. As a reward he received £500 plus a horse equipped with a saddle and bridle. 

The diamond weighed 971 old carats, equivalent to 995.2 metric carats. It possessed the fore mentioned blue-white color characteristic of the finest Jagersfontein diamonds, especially cleavages, and was of very fine quality, although there were a number of internal black spots, another Jagersfontein characteristic. The shape of the stone was out of the ordinary: flat on one side and rose to a peak on the other, somewhat like a loaf of rye bread. Apparently this is what inspired the diamond to be named 'Excelsior', meaning higher. 

The Excelsior may justly lay claim to be the 'Great Unknown' of famous diamonds. As will be explained further along, there is no single Excelsior fragment of exceptional size which would have helped to keep its name in the public eye, thus helping keep track of the fragments. In addition, except for having stimulated some interest among local diggers, the finding of such a large stone seems to have made singularly little impact. No account of the discovery appeared in the more authoritative and prestigious British newspapers which often reported lesser discoveries at the time. Maybe if the diamond had been originally been given a less unglamorous name its fame might have spread further outside of South Africa.
The the Excelsior ranks as the second largest rough diamond of gem quality ever found, only the Cullinan being larger. 
After prolonged study it was decided to first cleave the diamond into ten pieces: this operation which was performed by Mr. A. Asscher, resulting in the three largest pieces weighing 158, 147 and 130 carats. The polishing was supervised by Henry Koe and yielded 21 gems, ranging from 70 carats to less than 1 carat. They totaled 373.75 carats which represented a loss in weight of almost 63 percent. The final result, however, was considered to have been better than anyone had expected.

The specifications of the larger gems cut from the Excelsior are as follows:

• Excelsior I: 69,68 ct. Pear Shape

• Excelsior II: 47,03 ct. Pear Shape

• Excelsior III: 46,90 ct. Pear Shape

• Excelsior IV: 40,23 ct. Marquise

• Excelsior V: 34,91 ct. Pear Shape

• Excelsior VI: 28,61 ct. Marquise

• Excelsior VII: 26,30 ct. Marquise

• Excelsior VIII: 24,31 ct. Pear Shape

• Excelsior IX: 16,78 ct. Pear Shape

• Excelsior X: 13,86 ct. Pear Shape

• Excelsior XI: 9,82 ct. Pear Shape

The Excelsior gems were sold separately, three of them were bought by Tiffany & Co., in their old store in Union Square in New York City. The names of the other buyers have not been disclosed but it is known that De Beers displayed one of the marquise-shaped fragments at the 1939 World's Fair in New York.