Chiral crystals are also called enantiomorph crystals. The best known examples of chiral crystals are quartz crystals. To distinguish between the two enantiomorph structures of enantiomorph crystals, the prefixes (+)- vs. (-)- can be used, which correspond to the prefixes d- vs. l-. Consequently, we distinguish between (+)-d-quartz and (-)-l-quartz. Other enantiomorph crystals which have played an important role in discussions on the origin of biomolecular asymmetry are sodium chlorate NaClO3, the triclinic space group of pyrite FeS2, as well as specific montmorillonite modifications. Crystals of calcite are, however, non-chiral. In general, the crystal's structure is determined by its space group. Among a total of 230 space group types that are in use by mineralogists for the systematic classification of three-dimensional structures of crystals and minerals, about 60 space group types give rise to chiral crystals.
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