Desert rose is the colloquial name given to rosette formations of the minerals gypsum

Gypsum

Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...

 and barite

Barite

Baryte, or barite, is a mineral consisting of barium sulfate. The baryte group consists of baryte, celestine, anglesite and anhydrite. Baryte itself is generally white or colorless, and is the main source of barium...

 with poikilotopic sand inclusion

Inclusion (mineral)

In mineralogy, an inclusion is any material that is trapped inside a mineral during its formation.In gemology, an inclusion is a characteristic enclosed within a gemstone, or reaching its surface from the interior....

s. The 'petals' are crystals flattened on the c crystallographic axis, fanning open along characteristic gypsum cleavage planes.

The rosette crystal habit

Crystal habit

Crystal habit is an overall description of the visible external shape of a mineral. This description can apply to an individual crystal or an assembly of crystals or aggregates....

 tends to occur when the crystals form in arid sandy conditions, such as the evaporation of a shallow salt basin. Gypsum roses usually have better defined, sharper edges than barite roses.

The desert rose may also be known by the names:

• sand rose
• rose rock
  Rose Rock
  Rose rocks are aggregates of barite crystals and sand whose iron content gives them a reddish hue. The barite crystals form a circular array of flat plates, giving the rock a shape similar to a rose blossom. Rose rocks appear either as a single rose-like bloom or as clusters of blooms, with...
  
  
• selenite rose
• gypsum rose
• gypsum rosette
• barite rose