Natural Desert Roses

Desert roses are crystals which usually take the form of rose petal. They have definite crystal shapes, and enclose sand grains. A gypsum rosette is not a rose at all, it is a mineral which crystalizes in a unique rosette growth pattern.

Desert rose is the colloquial name given to rose-like formations of crystal clusters of gypsum or baryte which include abundant sand grains.The 'petals' are crystals flattened on the c crystallographic axis, fanning open in radiating flattened crystal clusters.

Gypsum is an evaporite, which means its crystals form during the evaporation of water. The crystals are shaped like prisms or flat plates, and can grow up to 1 meter. Gypsum can appear as transparent crystals (selenite); fibrous, elongated crystals (satin spar); granular and compact masses (alabaster); and in rosette-shaped aggregates called desert roses.

Natural Desert Roses. Large cluster of Desert Rose crystals, Chihuahua, Mexico.
Credit: CrystalMiner

Some even form large clusters comprised of many small rosette crystals which are the color of sand and usually brown. In order for gypsum rosettes to form they must have an arid environment, a large source of CaSO₄(calcium sulfate), and a seasonal fluctuation of water. In terms of geological time gypsum rosettes form very rapidly in that they form in tens to hundreds of years. This would explain their abundance across the world.

The rosette crystal habit tends to occur when the crystals form in arid sandy conditions, such as the evaporation of a shallow salt basin. The crystals form a circular array of flat plates, giving the rock a shape similar to a rose blossom. Gypsum roses usually have better defined, sharper edges than baryte roses. Celestine and other bladed evaporite minerals may also form rosette clusters. They can appear either as a single rose-like bloom or as clusters of blooms, with most sizes ranging from pea sized to 4 inches (10 cm) in diameter.

There are two typical forms of rosettes found.

In more shallow regions is an amber colored compact ball of intergrown crystals with small, thin blades pointing out from the core seems to be the standard.. Sometimes large transparent amber blades protrude out of this core producing spectacular specimens.
In deeper layers, the crystals in the rosette are larger, more distinct and blocky. The color in these specimens are typically yellow, but can also be colorless. Large blades protruding from these rosettes are also blocky.

In both forms, some of the large blades may have clay or a rock included. All the crystals are fluorescent and phosphorescent, glowing a pale white under ultraviolet light.

Identification

Chemical formula: CaSO₄·2H₂O.
Crystal system: Monoclinic
Streak: White
Luster: Vitreous to silky, pearly, or waxy
Cleavage: Perfect on, distinct on {100}
Fracture: Conchoidal on, splintery parallel to [001]