Editing Crystal (section)

=== Rocks ===
By volume and weight, the largest concentrations of crystals in the Earth are part of its solid [[bedrock]]. Crystals found in rocks typically range in size from a fraction of a millimetre to several centimetres across, although exceptionally large crystals are occasionally found.  {{As of|1999}}, the world's largest known naturally occurring crystal is a crystal of [[beryl]] from Malakialina, [[Madagascar]], {{convert|18|m|abbr=on}} long and {{convert|3.5|m|abbr=on}} in diameter, and weighing {{convert|380,000|kg|abbr=on}}.<ref>G. Cressey and I. F. Mercer, (1999) ''Crystals'', London, Natural History Museum, page 58</ref>

Some crystals have formed by [[magmatic]] and [[metamorphic]] processes, giving origin to large masses of crystalline [[rock (geology)|rock]]. The vast majority of [[igneous rocks]] are formed from molten magma and the degree of crystallization depends primarily on the conditions under which they solidified. Such rocks as [[granite]], which have cooled very slowly and under great pressures, have completely crystallized; but many kinds of [[lava]] were poured out at the surface and cooled very rapidly, and in this latter group a small amount of amorphous or [[glass]]y matter is common. Other crystalline rocks, the metamorphic rocks such as [[marble]]s, [[mica-schist]]s and [[quartzite]]s, are recrystallized. This means that they were at first fragmental rocks like [[limestone]], [[shale]] and [[sandstone]] and have never been in a [[molten]] condition nor entirely in solution, but the high temperature and pressure conditions of [[metamorphism]] have acted on them by erasing their original structures and inducing recrystallization in the solid state.<ref name=EB1911>{{EB1911 |wstitle=Petrology |volume=21 |first=John Smith |last=Flett|inline=1}}</ref>

Other rock crystals have formed out of precipitation from fluids, commonly water, to form [[druse (geology)|druses]] or [[quartz]] veins. [[Evaporite]]s such as [[halite]], [[gypsum]] and some limestones have been deposited from aqueous solution, mostly owing to [[evaporation]] in arid climates.