Definition: Almeliite is a type of aluminium-bearing mineral that forms in acidic soils and water bodies, such as rivers and lakes. It can also occur as an intercalated mineral in granites with high alkali content. Almeliite exhibits a lustrous metamorphic crystalline structure composed of two orthorhombic units linked by long, linear crystal faces. The crystal faces are aligned along the [001] direction and exhibit strong cataclastic polycrystalline texture. Almeliite is a black-grey to dark brown mineral with a fine-grained, homogeneous texture that ranges in size from less than 0.1 mm to as large as several millimetres. It can be distinguished from aluminium sulfide (alumina) by its lustrous metamorphic crystalline structure.
almeriite