Chapter 4, Problem 1GST

To determine

Whether all the crystals in an intrusive igneous rock are of same size.

Answer to Problem 1GST

Not all the crystals in an intrusive igneous rock are of same size, because the rising body of magma experiences different rate of cooling temperature and then solidifies into different sizes of crystals. Different sizes of crystals in the same intrusive igneous rock are common.

Explanation of Solution

Magma is a naturally occurring melt of rocks and it contains many ions of the silicate minerals, mainly silicon and oxygen, gases, water vapor and some solids. When magma starts to cool, the ions present in the magma will self-arrange into different type of patterns, this process is called crystallization.

The size of a crystal is strongly influenced by the rate of cooling behavior of magma. The slow cooling of magma that led to the formation of larger crystals and less number of crystals. This is because the ions present in the magma have the ability to move larger distances, when slow cooling occurs.

The faster cooling of magma led to the formation of small intergrown crystals. This is because the ions present in the magma can lose the ability to move and they combine with each other rapidly.