Partheite or parthéite is a calcium aluminium silicate and a member of the zeolite group of minerals, a group of silicates with large open channels throughout the crystal structure, which allow passage of liquids and gasses through the mineral. It was first discovered in 1979 in rodingitic dikes in an ophiolite zone of the Taurus Mountains in southwest Turkey. The second discovery occurred in gabbro-pegmatites in the Ural Mountains, Russia. Since its discovery and naming, the chemical formula for partheite has been revised from CaAl2Si2O8•2H2O to include not only water but hydroxyl groups as well. The framework of the mineral is interrupted due to these hydroxyl groups attaching themselves to aluminum centered oxygen tetrahedra. This type of interrupted framework is known in only one other zeolite, the mineral roggianite. As a silicate based mineral with the properties of a zeolite, partheite was first described as zeolite-like in 1984 and listed as a zeolite in 1985. Partheite and lawsonite are polymorphs. Associated minerals include prehnite, thomsonite, augite, chlorite and tremolite. Composition Partheite is a calcium alumino-silicate with the chemical formula Ca2Al4Si4O15(OH)2∙4(H2O). This is a revised version of the formula reported initially as CaAl2Si2O8•2(H2O) that was determined using electron microprobe analysis. A new formula was necessary after structural analysis revealed the presence of hydroxyl groups in the structure. This new formula fell within the error limits of the initial electron microprobe analysis performed after the mineral was discovered in 1979. Zeolites have alkali or alkai-earth ions bonded to the main alumino-silicate framework, as well as water molecules that take extra-framework spaces. Partheite is different from most zeolites in that it contains the extra hydroxide ions, but is still considered a zeolite by the Subcommittee on Zeolites of the International Mineralogical Association. Structure Partheite’s crystal system is monoclinic with class 2/m and space group C2/c. It is structured with oxygen surrounding both the aluminum and silicon atoms in tetrahedral formation. These oxygen and aluminum tetrahedra connect by their corners. It is a sorosilicate because two silicate tetrahedra connect at their corners and an aluminum tetrahedra is then attached to each end forming a zig-zag structure. Every second aluminum tetrahedron is attached to a hydroxide ion and the structure is interrupted. The oxygen tetrahedra connect in ladder-like chains to form large 10-membered rings as well as 8-membered, 6-membered, and two types of 4-membered rings. The calcium atoms and water molecules cross through the structure