Two pear-shaped diamonds larger than 100 carats — one D-flawless and the other fancy deep orange-brown — will headline Sotheby's Magnificent Jewels auction in New York on June 16.

Named "Juno" to honor the ancient Roman queen of the gods, the 101.41-carat, D-color, internally flawless rarity is expected to fetch more than $10 million. Sotheby's noted that the appearance of a 100-carat perfect diamond at auction is a noteworthy event. Only 11 such stones have sold at auction since 1990, and Sotheby’s has had a hand in seven of those sales.

The Gemological Institute of America noted that Juno is a Type IIa diamond, which means that it is colorless and chemically pure with no traces of nitrogen or boron impurities.

The pear-shaped gem measures 38.49 x 27.18 x 17.55mm, about the diameter of a ping pong ball at its widest point.

"Earth Star" boasts a rich history that dates back to the presidency of Lyndon B. Johnson. The 111.59-carat, fancy deep orange-brown diamond was crafted from a 248.90-carat rough discovered at the Jagersfontein mine in South Africa in 1967.

The rough stone had emerged from a depth of 2,500 feet, which was exceptionally deep for a gem of this size, according to Sotheby's. The find was also notable because the mine previously had not been known to produce brown diamonds or diamonds of such a large size.

The stone was later sent to Baumgold Brothers in New York, which fashioned it into the pear shape we see today. The cutters at Baumgold Brothers called the finished diamond Earth Star due to its high level of brilliance.

In 1971, the diamond returned to South Africa for an exhibition commemorating the 100th anniversary of the discovery of the Kimberley mine. And then, in 1983, the Earth Star was sold at auction for nearly $1 million. The diamond has been in private hands ever since.

Earth Star has the distinction of being one of the 80 gems reviewed in the authoritative book by Lord Ian Balfour called Famous Diamonds.

David Webb designed a custom mounting for the orange-brown gem using azurmalachite to resemble the Earth as seen from the perspective of a star. The Earth Star diamond is being offered without reserve and Sotheby's published a pre-sale estimate of $1.5 million to $2.5 million.

Credits: Photos courtesy of Sotheby’s.