The correct answer is - True.
Depending on the quickness of the cooling of the magma, the size of the crystals is determined. If the magma is o=cooling on the surface or in a water body, than the cooling will be very quick, thus resulting in crystal of much smaller size, often not big enough to be seen with a bear eye. On the other hand, if the magma is cooling deeper into the ground, than it cools of much slower because of the high temperatures and pressures, which contributes to the creation of bigger clearly defined mineral crystal forms.
