A makhtesh (Hebrew: מכתש, plural: מכתשים - "makhteshim") is a geological landform regarded to be unique to the Negev desert of Israel and the Sinai Peninsula. Although commonly known as "craters" (a literal reading of the Hebrew, and due to the visual similarity), these formations are more accurately described as erosion cirques.
Giv'at Ga'ash, a black hill in the north of the makhtesh was once an active volcano which erupted thousands of years ago and caused it to be covered in lava which quickly cooled in the open air, converting it into basalt. Limestone covered by basalt can also be found in smaller black hills in the southern part of the makhtesh, including Karnei Ramon.
Shen Ramon (Ramon's Tooth) is a rock made of magma which hardened whilst underground. It later rose up through cracks in the earth's surface, and today stands in striking contrast with the nearby creamy coloured southern wall of the crater, as a black sharp-edged rock.