A botryoidal ( ) texture or mineral habit, is one in which the

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

has an external form composed of many rounded segments, named for the Ancient Greek (), meaning "a

bunch of grapes In viticulture, the grape cluster (also bunch of grapes) is a fertilized inflorescence of the grapevine, the primary part of this plant used for food (grape leaves are also used in some culinary traditions). The size of the grape bunch greatly va ...

".Adjective form: ''botruoeidēs''
This is a common form for many minerals, particularly

hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...

and

malachite Malachite () is a copper Carbonate mineral, carbonate hydroxide mineral, with the chemical formula, formula Basic copper carbonate, Cu2CO3(OH)2. This opaque, green-banded mineral crystallizes in the monoclinic crystal system, and most often for ...

, which are known for frequently forming botryoidal masses. It is also a common form of

goethite Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the α- polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient t ...

smithsonite Smithsonite, also known as zinc spar, is the mineral form of zinc carbonate ( Zn CO3). Historically, smithsonite was identified with hemimorphite before it was realized that they were two different minerals. The two minerals are very similar in a ...

fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs scal ...

, and chrysocolla. Similar habits are ''reniform'' (kidney-shaped) and ''mammillary'' (breast-shaped or partial spheres).

Formation

Minerals take on a botryoidal habit when they form in an environment containing many nuclei, specks of sand, dust, or other particulate matter to serve as sources of crystal nucleation. Acicular or fibrous crystals grow outward from these "seeds" at the same or very similar rate, resulting in radial

crystal growth Crystal growth is a major stage of a crystallization, crystallization process, and consists of the addition of new atoms, ions, or polymer strings into the characteristic arrangement of the crystalline lattice. The growth typically follows an ini ...

. As these spheres grow, they can run into or overlap with others that are nearby, fusing together to form a botryoidal cluster. Since botryoidal growths are formed from many smaller crystals, botryoidal habit is usually independent of the specific

crystal structure In crystallography, crystal structure is a description of ordered arrangement of atoms, ions, or molecules in a crystalline material. Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that repeat ...

associated with any given mineral. This is how the habit can be observed in a variety of minerals that otherwise display distinct euhedral forms.

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 Mineral habits