berlinite

Berlinite is a rare mineral with the chemical composition AlPO4. It is the aluminum phosphate mineral whose structure is isostructural with quartz, consisting of a three-dimensional framework formed by alternating AlO4 and PO4 tetrahedra linked through shared oxygen atoms. Crystallizes in the trigonal crystal system and occurs as colorless to pale yellow transparent to translucent crystals or in fine-grained masses. Typical crystal habit is prismatic or acicular, but crystals are uncommon.

It forms in phosphate-rich igneous rocks and hydrothermal veins, often in pegmatites, and is commonly found in association with quartz, apatite, and other phosphate minerals. The mineral is named berlinite after Berlin, Germany, reflecting the place of its discovery or description.