The Arabian Peninsula’s Empty Quarter, known as Rub’ al Khali, is the world’s largest sand sea, holding about half as much sand as the Sahara Desert. The Rub’ al Khali covers 650,000 km2 (225,000 square miles), and stretches over parts of Saudi Arabia, Yemen, Oman, and the United Arab Emirates. It is part of the larger Arabian Desert.
The desert is 1,000 kilometres long, and 500 kilometres wide. Its surface elevation varies from 800 metres in the southwest to around sea level in the northeast. The terrain is covered with sand dunes with heights up to 250 metres, interspersed with gravel and gypsum plains. The sand is of a reddish-orange color due to the presence of feldspar.
The region is classified as "hyper-arid", with annual precipitation generally less than 35 millimetres (1.4 in), and daily mean relative humidity of about 52% in January and 15% in June–July. Daily maximum temperatures average 47 °C (117 °F) in July and August, reaching peaks of 51 °C (124 °F). The daily minimum average is 12 °C (54 °F) in January and February, although frosts have been recorded. Daily extremes of temperature are considerable.
Fauna includes arachnids (e.g. scorpions) and rodents, while plants live throughout the Empty Quarter. As an ecoregion, the Rub' al Khali falls within the Arabian Desert and East Saharo-Arabian xeric shrublands. The Asiatic cheetahs, once widespread in Saudi Arabia, are regionally extinct from the desert.
The Shaybah oil field was discovered in 1968. South Ghawar, the largest oil field in the world, extends southward into the northernmost parts of the Empty Quarter.
According to wikipedia