Foliation is more likely to occur during mountain building (orogenesis) than through the contact of rock with magma due to the nature and scale of the forces involved. Here's a breakdown:

Mountain Building:

* Intense Pressure and Deformation: During mountain building, tectonic plates collide, leading to immense pressure and shearing forces. This squeezes and deforms rocks, aligning mineral grains in a preferential direction, resulting in foliation.

* Regional Metamorphism: The pressure and heat associated with mountain building cause regional metamorphism, which transforms rocks and further promotes foliation.

* Large-Scale Deformation: The forces acting during orogenesis often affect vast regions of rock, facilitating the development of extensive foliation planes.

Contact Metamorphism (magma contact):

* Localized Heat and Pressure: While magma contact does generate heat and pressure, these are localized and primarily affect the rock immediately adjacent to the magma intrusion.

* Limited Deformation: The pressure exerted by magma intrusion is often insufficient to cause significant deformation or alignment of minerals throughout a large rock body.

* Contact Aureole: The zone of rock altered by magma contact (contact aureole) is usually relatively small compared to the extensive areas affected by mountain building.

In summary:

* Mountain building involves intense pressure and widespread deformation, creating the ideal conditions for foliation to develop.

* Contact metamorphism, while involving heat and pressure, typically lacks the widespread deformation necessary for significant foliation development.

While foliation can occur in both scenarios, the scale and intensity of deformation during mountain building make it a far more conducive environment for the formation of foliated rocks.