Origin and structural character of haüyne_ss in spinel dunite xenoliths from La Palma, Canary Islands Available to Purchase

Two spinel dunite xenoliths (Fo_89.8–91.2 in olivine) from La Palma contain minor amounts (<1%) of a pale-blue sodalite-group mineral with haüyne/lazurite chemistry. Selected-area electron diffraction (SAED) patterns of this phase indicate a cubic unit cell with dimensions 9.12 ± 0.02 Å, and space group P4̅3n. Superstructure spots along three <110> directions are common, implying commensurate or incommensurate modulations along <110> directions. Raman spectra show peaks typical of both lazurite and haüyne. It is concluded that the mineral has a structure intermediate between those of pure lazurite and pure haüyne, and it is here referred to as haüyne_ss. The haüyne_ss occurs together with strongly nepheline-normative glass in thin veinlets (<0.1 mm), in interstitial glass pockets, and as inclusions in olivine porphyroclasts. To our knowledge lazurite or haüyne has not previously been described in mantle rocks. The haüyne_ss is strongly depleted in REE and most other highly lithophile elements relative to the coexisting glass, whereas D_{mineral/glass} for Sr is ≈1.0, and D_Eu higher than the other REE. The haüyne_ss crystallized from a melt now present as phonolitic glass, probably in response to rapidly decreasing pressure during transport of the xenoliths to the surface. The coexistence of haüyne_ss and FeS-rich sulfide globules in some samples suggests slightly more oxidizing conditions than for samples in which the glass contains sulfide globules alone.