Species, variety and a growth habit
Selenite is gypsum. Desert rose is a habit that can involve gypsum OR barite, so it is cross-listed rather than universally identified as gypsum.
Keep each chapter’s scientific identity: a family, species, variety, trade label, rock and fossil are different kinds of names.
Mineral variety
Selenite is the clear, crystalline variety of gypsum. Its thin plates and pearly surfaces reward gentle observation, while its very low hardness makes it a material to handle with particular care.
Darla Sondrol · CC0 · Display crop
Crystal habit / aggregate
A desert rose is a flower-like aggregate with sand caught among crystal blades. The name describes a formation: gypsum and barite can both produce rose-like specimens.
Didier Descouens · CC BY-SA 4.0 · Display crop