A survey of hybrid twins in non-silicate minerals.

Hybrid twins are twins in which two or more concurrent sublattices based on the same twin element exist. Each sublattice contributes, with its twin index and obliquity, to the overall degree of lattice restoration, which is measured by the effective twin index nE, a generalization of the classical twin index. A systematic analysis of twins in the following non-silicate minerals is presented and the hybrid nature of several of them is pointed out: apatite, anhydrite, aragonite, aramayoite, arsenic, atacamite, baddeleyite, becquerelite, bellingerite, brookite, butlerite, calcite, cassiterite, celestine, chalcostibite, corundum, cryolite, derbylite, diaphorite, dolomite, euxenite-(Y), columbite-(Fe) (also known as ferrocolumbite), glaucodot, gudmundite, gypsum, haindingerite, hausmannite, hematite, ilmenite, iodargyrite, linarite, kotoite, marcasite, maucherite, metarossite, millerite, monazite, nickeline, nitratine, proustite, pyrargyrite, raspite, sassolite, scorzalite, stannite, symplesite, ulexite, xenotime-(Y