The Collaborative International Dictionary
Botryoid \Bot"ry*oid\, Botryoidal \Bot`ry*oid"al\, a. [Gr. ? cluster of grapes + -oid.] Having the form of a bunch of grapes; like a cluster of grapes, as a mineral presenting an aggregation of small spherical or spheroidal prominences; as, botryoidal hematite.
Syn: botryose.
Wiktionary
a. (context chiefly mineralogy English) Having the form of a bunch of grapes.
WordNet
Wikipedia
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.
Usage examples of "botryoidal".
Not the least curious part of this outcrop is the black thread of iron silicate which, broken in places, subtends it to the east: some specimens have geodes yielding brown powder, and venal cavities lined with botryoidal quartz of amethystine tinge.
He has a face of that rubicund, knobby type I have heard an indignant mineralogist speak of as botryoidal, and about it waves a quantity of disorderly blond hair.