Question

3. Considering the relationship between cooling rate and crystal size in igneous rocks, describe in your own words what would you expect to see in igneous rock textures in the following situations.

Answer 1

Igneous texture depends on the cooling. The slower the cooling the bigger the crystal and better structure whereas faster cooling smaller crystal and not good texture.

Slower cooling will have panidiomorphic texture whereas faster cooling have allotriomorphic texture. Slow cooling have bigger crystal and faster cooling have smaller crystal more often glassy type of matter.

Also remember when colling is slow then euhedral crystal form and when cooling is slow then anhedral crystal forms.

B) Batholiths have bigger crystal because they crystallises at deeper depth that's why the colling is slow there. But when the Batholith will intrude into a rock then it will give a contact effect to the surrounding rock. There the rock will metamorphose and will give contact aureole metamorphic texture. That will show the contact facies like sanidinite facies, hornblende hornfelse facies etc.