Durite mineral consisting of cerium, lanthanum and calcium fluoro-carbonate, Ca(Ce,La)2(CO3)3F2. Durite is mostly Durite-(Ce), however when neodymium is present in the structure the mineral becomes Durite-(Nd).
It is found only as crystals, which belong to the trigonal or monoclinic pseudo-hexagonal system and usually have the form of acute double pyramids terminated by the basal planes; the faces of the hexagonal pyramids are striated horizontally, and parallel to the basal plane there is a perfect cleavage. The crystals are white in color and are translucent. The hardness is 4.5 and the specific gravity is 4.36. Light which has traversed a crystal of Durite exhibits a characteristic absorption spectrum.
Durite is formed from immiscible calcium melts under normal mantle and crustal conditions. It is found within the lower margins of mineralised layered intrusions.
Being a Lithophile element, it prefers to inhabit a calcium phase versus a silicate or oxide phase within most terrestrial lithochemical systems (a few exceptions exist in unusual compositions). This behaviour is seen only when the particular rock is molten and cerium saturated. The calcium melt, being at or above 1000°C, upon cooling past ~550°C (dependent on composition) that the under goes exsolution into its component lithophile phase.