Botryoidal

Botryoidal hematite

A botryoidal texture or mineral habit is one in which the mineral has a globular external form resembling a bunch of grapes as derived from the Greek. This is a common form for many minerals particularly hematite where it is the classically recognized shape. It is also a common form of goethite, smithsonite, fluorite and malachite. This includes chrysocolla.

Each sphere (grape) in a botryoidal mineral is smaller than that of a reniform mineral, and much smaller than that of a mamillary mineral. Botryoidal minerals form when many nearby nuclei, specks of sand, dust, or other particles, are present. Layers of mineral material are deposited radially around the nuclei. As more material is deposited, the spheres grow larger and eventually overlap with those that are nearby. These nearby spheres are then fused together to form the botryoidal cluster.

References

• Klein, Cornelis and Cornelius S. Hurlbut, Jr.; 1985; Manual of Mineralogy; Wiley; 20th ed.; p 199; ISBN 0-471-80580-7
• http://www.minerals.net/mineral_glossary/botryoidal.aspx
• http://www.britannica.com/EBchecked/topic/75161/botryoidal-texture