Lithops derives from the Greek words lithos and ops, "rock" and "shape" respectively in English, and halli for the collector, called Harry Hall. A curious plant that grows natively in South Africa. The height is about 20 centimeters, so it would be comparable to a small rock. Usually with two halves, the plant has a ticker base for storing water in a higher proportion.
In the middle, it has a fissure and the flowers appear in it. If you search for the Lithops hallii the first place to look are limestone terrains, within dark sandstone or other fine-grained stones.
There are multiple varieties with different colors and geometry. A variety called Lithops hallii Gelkop has a very interesting white flower, almost as big as the entire base. But, there are other as amazing or more!
This web page as great information about its cultivation and varieties. It defines it as “some of the world's most fascinating plants”.
Here is the link.