large crystals result from very slow cooling.
evaporation of water: this would produce an evaporite which is a sedimentary rock. like a salt pan in a desert. not possible to have volcanic rocks originate this way.
crystalization in molten earth: slow cooling over time. (hundreds to millions of years)
crystalization at earth's surface: this results in fast cooling. (a few hours to a few months or years)
crystalization from cooling off hot water: that would be a hydrothermal deposit. while associated with volcanics they are not volcanic rocks themselves and usually occur fairly rapidly.