13 Organigenic crystals Many living organisms are able to produce crystals, for example calcite and aragonite in the case of most molluscs or hydroxylapatite in the case of vertebrates.Large single crystals can be created by geological processes.Occurrence in nature Ice crystals Rocks By volume and weight, the largest concentrations of crystals in the Earth are part of its solid bedrock.
This article is about crystalline solids.It can form a single crystal, perhaps with various possible phases, stoichiometries, impurities, defects, and habits.For example, diamond is among the hardest substances known, while graphite is so soft that it is used as a lubricant.
11 Other rock crystals have formed out of precipitation from fluids, commonly water, to form druses or quartz veins.Citation needed A single snowflake is a single crystal or a collection of crystals, 12 while an ice cube is a polycrystal.Image gallery Hoar frost : A type of ice crystal (picture taken from a distance of about 5 cm).
For example, diamond and graphite are two crystalline forms of carbon, while amorphous carbon is a noncrystalline form.For example, selenite crystals in excess of 10 meters are found in the Cave of the Crystals in Naica, Mexico."Chem1 online textbookStates of matter".
The International Union of Crystallography has redefined the term "crystal" to include both ordinary periodic crystals and quasicrystals any solid having an essentially discrete diffraction diagram" 16 ).But unlike a grain boundary, the orientations are not random, but related in a specific, mirror-image way.