Suppose that a biker bikes into the wind for 84 miles and it takes him 7 hours. After a long rest, he returns (with the wind on his back) in 6 hrs. Determine the speed at which biker can ride his bike in still air and the effect that the wind had on his speed.

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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.