2
زمینشناسی و معدن::
تشکیل بلور
At moderate temperatures and atmospheric pressure minerals may be dissolved, or crystallize out, through the action of meteoric groundwater.
If conditions deviate from the 'stability field' of one species, another species which is stable in the new environment will preferentially crystallize out.
igneous minerals, crystallized out from magmatic melts, arc dominated by silica and certain groups of silicate minerals - the feldspars, fcldspatholds, pyroxenes, amphiboles, micas nnd members of the olivine group.
If fractional crystallization of the magma takes place, late-stage concentration of rare elements and a supply of fluorine- and boron-bearing volatiles permit the formation of an additional assemblage of minerals typifying the pegmatitic environment - tourmaline, apatite, fluorite, beryl, topaz, wolframite, a range of metallic sulphides and oxides, including cassiterite and those of the rare earth elements.
Many are also formed under pneumatolytic and hydrothermal conditions: crystallization from hot gases and waters enriched with dissolved elements.
واژگان شبکه مترجمین ایران