2.1" Lustrous Hemimorphite Crystal Cluster on Mimetite - Congo

Hemimorphite is a basic hydrous zinc silicate with the chemical composition Zn4Si2O7(OH)2 · H2O. It earned its name from the Greek terms that best define its crystal structure. It has two different terminations on each side of the crystal, hence the inclusion of the greek terms "hemi", meaning half, and "morph", meaning shape. The crystal formations can range anywhere between a crystal druze or botryoidal formation to radiating acicular crystals and more. Hemimorphite has been found in shades of white, beige, light brown, and a bright, electric blue. It can also form as yellow and green crystals on rare occasions.

Prior to 1803, hemimorphite and smithsonite were thought to be the same mineral, called "calamine". However, further scientific research concluded that these were two distinct minerals.

Mimetite is a lead chloro-arsenate mineral with the chemical formula of Pb5(AsO4)3Cl. Depending on conditions during formation/replacement, arsenate radicals (As04) can be replaced by a phosphate (PO4) or vanadate (VO4) radical. This alteration is what leads to the formation of pyromorphite and vanadinite, hence why they are typically found associated with each other. Often red to yellow in color, mimetite can occur in a variety of structures, from small prismatic clusters and crusts to incredible hexagonal crystals both thick and thin.