The discovery was made by a Yutu 2 drive team member in July 2019, during lunar day 8 of the rover's mission, which is part of China's Chang'e 4 mission to explore the far side of the moon.
This description, along with the initial absence of images, sparked wide interest as well as speculation among lunar scientists.
The authors describe the material as a dark greenish and glistening impact melt breccia, measuring 20 inches by 6 inches (52 by 16 centimeters).
According to the paper, the breccia — broken fragment of minerals cemented together — was formed by impact-generated welding, cementing and agglutinating of lunar regolith and breccia.
The material, they say, resembles lunar impact melt breccia samples returned by NASA's Apollo missions.
In particular, similarities with the Apollo samples designated 15466 and 70019 are noted, a comparison made earlier by lunar scientist Clive Neal at the University of Notre Dame.
The measurements lead the authors to suggest the lunar regolith consists of a mixture from multiple sources.
The Chang'e 4 spacecraft made its historic landing in the 110-mile-wide (180 kilometers) Von Kármán Crater on the far side of the moon in January 2019.
(One lunar day is about two Earth weeks long, as is a lunar night.) During lunar day 19, which began on June 14, the rover had driven a total of 51 feet (15.58 meters) across the lunar surface
The rover spent its 19th lunar morning investigating a small crater containing reflective material which could be another impact melt glass sample before continuing northwest
Yutu 2 and the Chang'e 4 lander powered down on June 27 (Chinese), bringing an end to lunar day 19