A new study offers clues to the mysteries of kimberlite eruptions, the source of most of the diamonds mined on Earth today.

As President Vladimir V. Putin of Russia prepares to host African leaders at a summit, a collapsed grain deal and the uncertain fate of Wagner mercenaries have cast a shadow.

The presidency of the West African country said that members of the presidential guard were trying to rally the military in an “anti-republican move.” The president’s fate was unclear.