The correct answer is - magma.
The molten rock coming from the mantle layer is called magma when it is deep into the ground, and lava when it manages to get lout on the surface. This molten rock, be it lava or magma, is the one responsible for the creation of mineral crystals. The crystals tend to have different shapes and sizes, and the reasons for that is the way of their formation. The lava cools of very quickly because the surface is much cooler, thus not giving enough time for larger crystals to form. The magma cools off much slower because it is hotter inside the crust, thus the crystals grow much larger as they have much more time to do so. Both the lava and the magma create igneous rocks.