Formation of end-member NaAlSi3O8 hollandite-type structure (lingunite) in diamond anvil cell

The existence of end-member NaAlSi3O8 hollandite-type structure (lingunite) as a result of high-pressure phase transition of a natural albite is investigated between 15 and 30 GPa at 2000 °C, using laser-heated diamond anvil cells. X-ray analysis of the quenched samples showed that albite transforms to jadeite plus stishovite at ∼17 GPa, and to a hollandite-type structure between ∼19 and ∼23 GPa, with further decomposition to NaAlSiO4 calcium ferrite-type structure plus stishovite at higher pressures. The formation of hollandite-type structure in the limited range of pressure at high temperatures may elucidate the conditions of meteoritic impacts, where this mineral has been formed naturally. Calcium ferrite-type structure, however, is the only stable dissociation product of albite under the deep lower mantle conditions.