Editing Calcite (section)

=== Crystal habits ===
Calcite has numerous habits, representing combinations of over 1000 [[crystallographic form]]s.<ref name=HOM/>  Most common are [[scalenohedron|scalenohedra]], with faces in the hexagonal {{mset|2 1 1}} directions (morphological unit cell) or {2 1 4} directions (structural unit cell); and rhombohedral, with faces in the {{mset|1 0 1}} or {{mset|1 0 4}} directions (the most common cleavage plane).<ref name=Hazen/> Habits include acute to obtuse rhombohedra, tabular habits, [[Prism (geometry)|prisms]], or various [[scalenohedron|scalenohedra]]. Calcite exhibits several [[crystal twinning|twinning]] types that add to the observed habits. It may occur as fibrous, granular, lamellar, or compact. A fibrous, efflorescent habit is known as ''lublinite''.<ref>{{cite web|title=Lublinite|url=http://www.mindat.org/min-9512.html|website=mindat.org|access-date=6 May 2018}}</ref> Cleavage is usually in three directions parallel to the rhombohedron form. Its fracture is [[Conchoidal fracture|conchoidal]], but difficult to obtain.

Scalenohedral faces are [[chiral]] and come in pairs with mirror-image symmetry; their growth can be influenced by interaction with chiral biomolecules such as L- and D-[[amino acid]]s. Rhombohedral faces are not chiral.<ref name=Hazen/><ref>{{Cite journal |last1=Jiang |first1=Wenge |last2=Pacella |first2=Michael S. |last3=Athanasiadou |first3=Dimitra |last4=Nelea |first4=Valentin |last5=Vali |first5=Hojatollah |last6=Hazen |first6=Robert M. |last7=Gray |first7=Jeffrey J. |last8=McKee |first8=Marc D. |date=2017-04-13 |title=Chiral acidic amino acids induce chiral hierarchical structure in calcium carbonate |journal=Nature Communications |language=en |volume=8 |issue=1 |pages=15066 |doi=10.1038/ncomms15066 |pmid=28406143 |pmc=5399303 |bibcode=2017NatCo...815066J |issn=2041-1723}}</ref>

<gallery class="center">
File:Estonian Museum of Natural History Specimen No 182279 photo (g28 g28-218 1 jpg).jpg|Rhombohedral calcite
File:Calcite jaune sur fluorine violette (USA).jpg|Scalenohedral calcite
File:Calcite, galène et pyrite (Dal'negorsk - Fédération de Russie).JPG|Prismatic calcite
File:Calcite et fluorine (USA).JPG|Prismatic calcite
File:Calcite 7.jpg|Stalactitic calcite
File:Estonian Museum of Natural History Specimen No 202078 photo (g27 g27-415 1 jpg).jpg|Hexagonal calcite
File:Calcite-241250.jpg|Dodecahedral calcite
File:Calcite - Galleria di Mezzolombardo (Trento) - Paolo Ferretti.jpg|Bipyramidal calcite
File:Muséum de Nantes - 352 - Calcite (Grenoble, Isère, France).jpg|Druse calcite
File:Natural History Museum 155 (8047048490).jpg|Twinned calcite
File:Calcite - Sassari, Sardegna, Italia 01.jpg|Globular calcite
File:Calcite (Cave-in-Rock Mining District, Illinois, USA) 3 (42590140555).jpg|Botryoidal calcite
</gallery>