Malachite (#39)

Aesthetic cluster of intergrown botryoids to 1" diameter.
Africa Mashamba West Mine, Near Kolwezi, Katanga, Congo 4 ½" x 2" x 1 ½"

 

Learn More


In some previous "Learn More"s, we have used the term "crystal habit" or "mineral habit," and the meaning has been related to the general shape of a specimen. The emphasis has been on how the unit cell - the imaginary box on a scale of Angstroms that contains all the chemistry and symmetry needed to fully describe the crystal structure - is expressed in the overall shape of the crystal. That is perfectly valid. But crystals sometimes form in clusters that obscure their individual shapes, but are nonetheless diagnostic of a particular mineral. Botryoidal malachite is very common.

Botryoidal habit (from Greek botrys, bunch of grapes) looks somewhat like a cluster of grapes. Each sphere consists of a very large number of needle-like crystals radiating from the center, and terminating in a surface that appears smooth and uniform. Depending on the sizes of the spheres, different terminology may be applied, but they all fall under the general heading of colloform structures. Sometimes minerals form colloform-banded textures, in which the radiating crystals have superimposed on them concentric banding of different colors or shades. Things can get very complex, and the geochemical factors that control such growth are not always obvious.