A mining company has announced plans to sell a collection of what it says are the most valuable diamonds ever cut in Russia. The largest in the collection is a 51.38-carat round cut diamond. It was produced by Russia’s Alrosa company as part of a special collection called Dynasty. The state-run Alrosa said the five-piece collection was named after the Romanov dynasty, which ruled Russia for 300 years. It is also meant to honor Russian ruler Peter the Great, who built the city of St. Petersburg. The company said Peter the Great started the country’s first diamond factory early in the 18th century. Alrosa calls the biggest piece the purest of all large diamonds manufactured throughout Russian jewelry history. The 51.38-carat diamond is 2.5 centimeters in diameter.